Author Topic: Open Source Multimeter  (Read 238233 times)

0 Members and 1 Guest are viewing this topic.

Offline House91320

  • Regular Contributor
  • *
  • Posts: 176
Open Source Multimeter
« on: June 30, 2011, 05:05:19 pm »
My friends and I have been developing an open source multimeter. I wanted to do a case design for a kick starter video, and i would like people to tell me what they think of the case so I can make it look as good as possible.
« Last Edit: June 30, 2011, 05:09:28 pm by House91320 »
 

Offline ndictu

  • Regular Contributor
  • *
  • Posts: 210
  • Country: sk
Re: Open Source Multimeter
« Reply #1 on: June 30, 2011, 05:19:42 pm »
Please don't be yet another one of those kickstarter projects that only have a rotating CAD model and long FAQ with answers to the most minutiae details, but no real proof-of-concept design.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #2 on: June 30, 2011, 05:24:08 pm »
It looks like a children's toy but it's only a prototype model.

How much are you planning to sell it for?
 

Offline House91320

  • Regular Contributor
  • *
  • Posts: 176
Re: Open Source Multimeter
« Reply #3 on: June 30, 2011, 05:30:42 pm »
Don't know yet i have to figure out the manufacturing cost.
 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #4 on: June 30, 2011, 05:51:49 pm »
My first question would be  WHY? The top end of the market is well served by the likes of Fluke et al. The budget end of the market is VERY price conscious and the low end is awash with One Hunglow Tat. This leaves the speciality sector, low volume and usually high accuracy. Without a very tight spec and a definite market to aim at you may find finance a rare resource.
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #5 on: June 30, 2011, 05:59:57 pm »
A good open source oscilloscope would be nice.
 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #6 on: June 30, 2011, 06:59:28 pm »
A good open source oscilloscope would be nice.
Again WHY? For the same reasons above they are just not cost effective. Unless you are doing it just for chuckles it makes no sense to me , sorry.
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #7 on: June 30, 2011, 07:00:36 pm »
There's the Nano, a crap open source 'scope so why not do the same thing with higher spec' hardware?
 

Online mikeselectricstuff

  • Super Contributor
  • ***
  • Posts: 12554
  • Country: gb
    • Mike's Electric Stuff
Re: Open Source Multimeter
« Reply #8 on: June 30, 2011, 07:21:04 pm »
A good open source oscilloscope would be nice.
Again WHY? For the same reasons above they are just not cost effective. Unless you are doing it just for chuckles it makes no sense to me , sorry.
A scope has MUCH more potential as an OS project as a lot of the cost on higher end commercial units is for software functionality. For the hardware cost of a Rigol you could in principle build something with the performance and features of a scope several times the price, although it would be a lot of work
A DMM seems pretty pointless as I can't see what you can do better/cheaper than what's already out there.
Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
Day Job: Mostly LEDs
 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #9 on: June 30, 2011, 07:44:35 pm »
A good open source oscilloscope would be nice.
Again WHY? For the same reasons above they are just not cost effective. Unless you are doing it just for chuckles it makes no sense to me , sorry.
A scope has MUCH more potential as an OS project as a lot of the cost on higher end commercial units is for software functionality. For the hardware cost of a Rigol you could in principle build something with the performance and features of a scope several times the price, although it would be a lot of work
A DMM seems pretty pointless as I can't see what you can do better/cheaper than what's already out there.
Hmm! Good point. Do you really think that SIGNIFICANT savings could be made in the hardware (without  cutting corners) to justify the effort of a home brew software firmware? I think Rigol do a pretty good job of squeezing every last cent out of there product (performance wise) and think they would be a hard act to beat. As a kickstarter project you need a significant edge, I just don't see it.
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

Online mikeselectricstuff

  • Super Contributor
  • ***
  • Posts: 12554
  • Country: gb
    • Mike's Electric Stuff
Re: Open Source Multimeter
« Reply #10 on: June 30, 2011, 07:49:13 pm »
A good open source oscilloscope would be nice.
Again WHY? For the same reasons above they are just not cost effective. Unless you are doing it just for chuckles it makes no sense to me , sorry.
A scope has MUCH more potential as an OS project as a lot of the cost on higher end commercial units is for software functionality. For the hardware cost of a Rigol you could in principle build something with the performance and features of a scope several times the price, although it would be a lot of work
A DMM seems pretty pointless as I can't see what you can do better/cheaper than what's already out there.
Hmm! Good point. Do you really think that SIGNIFICANT savings could be made in the hardware (without  cutting corners) to justify the effort of a home brew software firmware? I think Rigol do a pretty good job of squeezing every last cent out of there product (performance wise) and think they would be a hard act to beat. As a kickstarter project you need a significant edge, I just don't see it.
I think the key would be clever people doing smart stuff in FPGAs - The Chinese makers are not good at innovating- it;s always cheaper versions of higer-end stuff with poorly designed software. You're never going to get  insane bandwidths as you're constrained by available ADCs, but I think there is plenty of scope to get things like good update rates and DPO type functionality, as well as lots of protocol analysis type functions, which are the sort of things that come as high-cost add-ons to current scopes.
Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
Day Job: Mostly LEDs
 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #11 on: June 30, 2011, 07:49:22 pm »
There's the Nano, a crap open source 'scope so why not do the same thing with higher spec' hardware?
What? Make a crap high end scope? :o ;D. Sorry I'm in a funny mood tonight!
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #12 on: June 30, 2011, 07:52:47 pm »

I think the key would be clever people doing smart stuff in FPGAs - The Chinese makers are not good at innovating- it;s always cheaper versions of higer-end stuff with poorly designed software. You're never going to get  insane bandwidths as you're constrained by available ADCs, but I think there is plenty of scope to get things like good update rates and DPO type functionality, as well as lots of protocol analysis type functions, which are the sort of things that come as high-cost add-ons to current scopes.
Well that rules me out! :'(.
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

Offline Kiriakos-GR

  • Super Contributor
  • ***
  • !
  • Posts: 3525
  • Country: gr
  • User is banned.
    • Honda AX-1 rebuild
Re: Open Source Multimeter
« Reply #13 on: June 30, 2011, 08:06:10 pm »
I wanted to do a case design for a kick starter video, and i would like people to tell me what they think of the case so I can make it look as good as possible.

Well I think that I am looking at one Gossen range switch,
plus the bottom of the Fluke 28II painted red, with out the holster, and a bit more square !!  :)

Well I have a tip for you,  you are in a good path, but you have to surprise us !!
Yes SURPRISE US !!

Its hard to happen,  but if you are serious in what you do, it will not be that difficult.   
If you like to know what to avoid ?  Look at Extech.   ;)
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 2488
  • Country: us
Re: Open Source Multimeter
« Reply #14 on: June 30, 2011, 08:14:46 pm »
There's the Nano, a crap open source 'scope so why not do the same thing with higher spec' hardware?

The nano already costs $100, and doesn't have a real scope AFE and has a pathetic sample rate, and only one channel.  Put real spec hardware in there, and you are increasing the cost a lot.

Quote from: FreeThinker
Hmm! Good point. Do you really think that SIGNIFICANT savings could be made in the hardware (without  cutting corners) to justify the effort of a home brew software firmware? I think Rigol do a pretty good job of squeezing every last cent out of there product (performance wise) and think they would be a hard act to beat.

No, I don't think you can make the equivalent of the 50 MHz Rigol for less than the market price, just based on parts cost alone, at least not in the volume a small open hardware project would get.

The bottom end of the market is under tremendous price pressure.  Manufacturers are basically selling their cheapest models near cost (at their much larger volumes) and making their profit and recovering the development costs on the premium for higher end features -- extra channels, extra bandwidth, mixed signal, and so forth all cost proportionally more than the base model.

So I think the only place you could attack the scope market is to aim higher, and especially with analysis tools.  If you had a few really good mixed signal designers who had been made independently wealthy and wanted to build an open hardware oscilloscope platform in their free time, you might be able to design something like a 4 channel, 200 MHz mixed signal scope where the production costs were less than a comparable commercial unit.  They key then would be to be able to add in all of the bonus firmware stuff for free: the measurements, the pass/fail analysis, and the protocol decoders. 

If you did that right, you might end up with something that had the hardware cost and specs of the 200 MHz/4 channel Rigol, but all the unlock codes from the Agilent 3000X.  Of course, you aren't going to get the obscene waveform update rate and real-time advanced triggering and protocol decoding without the agilent ASIC.

There are two problems with this: it takes a really talented team a long time to design something that has the functionality of a higher end scope.  You have to find those guys and convince them to work for free.  Second, the scope you build is still going to end up costing considerably more than the $400 a lot of hobbyists already balk at paying.  You might end up with the most powerful $1600 scope that nobody buys because the target audience can't afford it, and the people who can afford it and want the features are more interested in getting a name brand scope with support than a hackable open platform.  Plus you still have to contend with the problem that the big players are sitting there with their ASICs that you can't match in terms of performance.
 

Offline tnt

  • Regular Contributor
  • *
  • Posts: 239
Re: Open Source Multimeter
« Reply #15 on: June 30, 2011, 08:54:06 pm »
Personally I'm convinced that an open source scope would be a good thing.

You're not going to get the low end market, I'd target something like 5000$ or so unit cost (I mean you do have to recoup the dev cost as well). But you could have in it a lot of the functionality of much higher priced scopes. Sure not every hobbyist is gonna buy it ... but I'm convinced there is enough of a market for it anyway. (I'm just a hobbyist/hacker and I have a 7500$ scope ...)

If you do the design modular enough (mostly front end separate from the acq) to allow modules for scope / logic analyzer / spectrum analyzer / ...

The agilent asic function could all be replaced by a good FPGA (I did and still do FPGA design for a living so I know what I'm saying). Agilent went the asic way because it's much cheaper given the volume they have and they're all about having more margin. But for a project like this, even 500$ of FPGA cost would be acceptable and for that price, you get a pretty good one that can definitely compute your 800x600 image composite of 50k wfrm/s in its internal memory.
 

Offline ivan747

  • Super Contributor
  • ***
  • Posts: 2027
  • Country: us
Re: Open Source Multimeter
« Reply #16 on: June 30, 2011, 10:58:40 pm »
There's the Nano, a crap open source 'scope so why not do the same thing with higher spec' hardware?
What? Make a crap high end scope? :o ;D. Sorry I'm in a funny mood tonight!
So am I! I have trolled all over the forum! Sorry.
 

Offline vtl

  • Regular Contributor
  • *
  • Posts: 136
  • Country: au
Re: Open Source Multimeter
« Reply #17 on: July 01, 2011, 02:21:42 am »
Markets pretty saturated for multimeters, how about a decent LCR meter that does ESR as well? Make it cost under $100 and you got a winner, seems like you have to pay double or triple that for something worthwhile.
For a hobbyist it doesn't sound great to spend that much to measure the ESR of a 10c cap of old electronics.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #18 on: July 01, 2011, 03:59:06 pm »
It would have to do RMS measurements too.
 

Offline Afrotechmods

  • Supporter
  • ****
  • Posts: 44
  • Country: 00
    • Afrotech
Re: Open Source Multimeter
« Reply #19 on: July 01, 2011, 07:27:30 pm »
As has been said before, I don't think you will actually be able to come up with a solution that will ever be able to compete with $40 off the shelf meters which are manufactured in quantities of 100+k.

However! I would like to applaud you for what you are doing anyway, because I think the real value in this project is the educational value. If you are able to document the project and the design process thoroughly it would be a cool thing to learn from. You could make money from putting ads up on the webpage documenting the project. I am particularly interested in the process of how you will design the case and get it manufactured, as industrial design is something I never got a chance to study in school.

Now to answer your questions, I think the design you've got so far looks pretty good. What does the D stand for by the way? Diode? If so, I recommend using the diode symbol instead. Also, I am used to seeing ºC instead of TMP.
The bright red on black looks a bit jarring. Perhaps a slightly more subdued red would look better.
 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #20 on: July 01, 2011, 07:55:55 pm »
As has been said before, I don't think you will actually be able to come up with a solution that will ever be able to compete with $40 off the shelf meters which are manufactured in quantities of 100+k.

However! I would like to applaud you for what you are doing anyway, because I think the real value in this project is the educational value. If you are able to document the project and the design process thoroughly it would be a cool thing to learn from. You could make money from putting ads up on the webpage documenting the project. I am particularly interested in the process of how you will design the case and get it manufactured, as industrial design is something I never got a chance to study in school.

Now to answer your questions, I think the design you've got so far looks pretty good. What does the D stand for by the way? Diode? If so, I recommend using the diode symbol instead. Also, I am used to seeing ºC instead of TMP.
The bright red on black looks a bit jarring. Perhaps a slightly more subdued red would look better.
As I understand it it's a kickstarter project.. he's looking for finance.
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

Offline Bored@Work

  • Super Contributor
  • ***
  • Posts: 3933
  • Country: 00
Re: Open Source Multimeter
« Reply #21 on: July 01, 2011, 08:40:11 pm »
As I understand it it's a kickstarter project.. he's looking for finance.

But the issues are the same. Would you finance a development which has that much >< of a change to become profitable?
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #22 on: July 01, 2011, 09:01:46 pm »
As I understand it it's a kickstarter project.. he's looking for finance.

But the issues are the same. Would you finance a development which has that much >< of a change to become profitable?
Exactly my point. See my first post :D
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

Offline tinhead

  • Super Contributor
  • ***
  • Posts: 1926
  • Country: 00
    • If you like my hacks, send me a donation
Re: Open Source Multimeter
« Reply #23 on: July 01, 2011, 10:06:25 pm »
there is handheld open source scope "ourdso", v2 is the latest revision, Based on Cyclone EP2C8Q208, as ADC the good known AD9288 (so 2 x 100MSs).
Based on NIOS , 320x240 ... far from perfect but it works already suficient. All sources available and actually can be easy modified to
support e.g. 2 x 500MSs or even 2 x 1GSs ADC, whatever.

But open source DMM ? For what reason ? Buy a 5USD single-chip DMM, few good resistors , attach cheap 8bit µC and here we go - DMM ready.
I don't want to be human! I want to see gamma rays, I want to hear X-rays, and I want to smell dark matter ...
I want to reach out with something other than these prehensile paws and feel the solar wind of a supernova flowing over me.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #24 on: July 02, 2011, 07:58:57 am »
But open source DMM ? For what reason ? Buy a 5USD single-chip DMM, few good resistors , attach cheap 8bit µC and here we go - DMM ready.
I don't think he's talking about building a basic meter.

I often think with Fluke, you're just paying for the name most of the time. It's true that Fluke offers good safety features and excellent accuracy which is why they're popular but they don't really cost much to build. A Chinese company could probably build a meter with the same accuracy and safety features as a Fluke but it's not worth their while as the kind of people who want them would just buy a Fluke and the cheap hobbyists would just buy a cheaper Chinese meter which doesn't have them.

I think an open source meter with the same accuracy and safety features of a Fluke would sell because people would be able to see the the quality of the components and would know that it's got the protection of a Fluke but at a lower price.
 

Offline Frant

  • Regular Contributor
  • *
  • Posts: 54
Re: Open Source Multimeter
« Reply #25 on: July 02, 2011, 11:41:12 am »
I think an open source meter with the same accuracy and safety features of a Fluke would sell because people would be able to see the the quality of the components and would know that it's got the protection of a Fluke but at a lower price.

I am not sure about this because of the safety aspect. Dave's teardowns showed us that safety of a multimeter relies not only on electronic components, but also on a specific case design. It might be possible to choose an existing handheld case from a good case manufacturer if there is a product that can meet the requirements. I see no point in designing an "open source" case that can only be economically fabricated in large series. There is also a complex range switch, probably a custom LCD and a custom keyboard. There is just too many specific parts, making it pointless to be an open source project.

Perhaps a modular benchtop PC-based instrument would be a better choice for an open source project. A decent metal case can be easily found, people would build their own modules for specific functions or as an upgrade, plenty of software possibilities etc. Something like a poor man's PXI or more like Agilent USB Modular Instruments, but much cheaper.
 

Offline Polossatik

  • Frequent Contributor
  • **
  • Posts: 295
  • Country: be
Re: Open Source Multimeter
« Reply #26 on: July 02, 2011, 03:38:38 pm »
there is handheld open source scope "ourdso", v2 is the latest revision, Based on Cyclone EP2C8Q208, as ADC the good known AD9288 (so 2 x 100MSs).
Based on NIOS , 320x240 ... far from perfect but it works already suficient. All sources available and actually can be easy modified to
support e.g. 2 x 500MSs or even 2 x 1GSs ADC, whatever.


can't find much about the "ourdso"  not listed here: http://www.opencircuits.com/Oscilloscope#Open_Source_Oscilloscopes

http://dangerousprototypes.com/2010/01/07/open-source-digital-sampling-oscilloscope/ tried it also one time

more on topic, I do not see any real value in making an OSS handheld multimeter, there is not much functionality you can add /improve on low cost existing ones  and price is also not a factor.
Real Circuit design time in minutes= (2 + Nscopes) Testim + (40 +120 Kbrewski) Nfriends

Testim = estimated time in minutes Nscopes= number of oscilloscopes present Kbrewski = linear approx of the nonlinear beer effect Nfriends = number of circuit design friends present
 

Offline House91320

  • Regular Contributor
  • *
  • Posts: 176
Re: Open Source Multimeter
« Reply #27 on: July 02, 2011, 09:55:36 pm »
It is suprizing how much reaction my post has created, wasn't expecting that. Well maybe i can clear up some stuff. The meter is going to have all the functions of a normal meter, volts, amps, ect, plus an esr meter, data logging, real time graphing, tft color screen, and user customization ui. I expect the price range to be between $100 and $200.
Also its going to use a rechargeable battery and is going to have USB and a corresponding software to do pc data logging and graphing.
« Last Edit: July 02, 2011, 10:02:57 pm by House91320 »
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #28 on: July 03, 2011, 01:02:39 am »
A have to agree with the many proponents that such a project hasn't got much likelihood of being funded and/or can't compete with commercial units.
It would have to offer something novel and a feature so compelling that you just have to have it.
If it's just a multimeter (but open source), I wouldn't bother.

Cool project as an exercise for sure, but that's all it is at present. It needs a killer feature.

Dave.
 

Uncle Vernon

  • Guest
Re: Open Source Multimeter
« Reply #29 on: July 03, 2011, 01:14:53 am »
A have to agree with the many proponents that such a project hasn't got much likelihood of being funded and/or can't compete with commercial units.
It would have to offer something novel and a feature so compelling that you just have to have it.
If it's just a multimeter (but open source), I wouldn't bother.

Cool project as an exercise for sure, but that's all it is at present. It needs a killer feature.

Dave.

I'll give this one the Led Zeppelin stamp too. You don't have to look much further than a Jaycar catalogue to see why.
A DIY DVM kit is priced high than an equivalent fully assembled and warranted junk Chinese DVM.
 

Alex

  • Guest
Re: Open Source Multimeter
« Reply #30 on: July 03, 2011, 01:18:33 am »
I expect the price range to be between $100 and $200.

That sounds like a truly great price for all the features! What did you consider to arrive at these figures House91320?
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #31 on: July 03, 2011, 01:43:28 am »
Also its going to use a rechargeable battery and is going to have USB and a corresponding software to do pc data logging and graphing.

Any isolation with that USB?

Battery life is very important in a hand held meter, beware.

Dave.
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #32 on: July 03, 2011, 01:51:08 am »
I see no point in designing an "open source" case that can only be economically fabricated in large series. There is also a complex range switch, probably a custom LCD and a custom keyboard. There is just too many specific parts, making it pointless to be an open source project.

Yeah, it gets messy. I'm just not sold yet on "yet another multimeter".
Sure it might have a ESR meter built in, and/or maybe LCR capability, but really, there is little differentiation with commercial handhelds.

It's gotta have something novel. I don't know what that is, but I'll know it if I see it!

Maybe something like a Fluke 233 with just the front end module, and the display can be anything. A watch, an iPhone, PC, whatever, or it just talks to you, or, something...

Like the iDVM concept that talks to your iPhone/iPad:


That's at least novel (but it's specs suck arse).

Stop the press!
I have a concept...
Might make a good blog.
House91320, can I show your images in the video?

Dave.
« Last Edit: July 03, 2011, 02:29:44 am by EEVblog »
 

Offline House91320

  • Regular Contributor
  • *
  • Posts: 176
Re: Open Source Multimeter
« Reply #33 on: July 03, 2011, 03:29:42 am »
Ya go ahead and use it in a video. In response to usb isolation it its going to have some opto coupling for the data lines and I am going to use a transformer and dc to ac converter for the isolation of the power.
 

Offline MrPlacid

  • Frequent Contributor
  • **
  • Posts: 277
  • Country: us
  • Hobby Hobbyist
Re: Open Source Multimeter
« Reply #34 on: July 03, 2011, 03:32:45 am »
Yeah, your open source multimeter must be completed with these feature:

Minimum, since these are already on the market:
-LCR
-Talking
-Dual trigger input like function to function as mini oscilloscope.
-Storage
-Temp
-Storage
-Watt meter
-luminosity
-audio meter
-High Voltage warning

Must be added in before release:
-Temperature reading without cable.
-Timer, UP, Down, Clock, Alarm clock (Talking timer too)
-Transmit wireless readings such as audio, video, photo, or just plain vanilla reading
 (You might skip the video part,  and use e-ink technology for photos. Black and white photo is better than nothing.)
-Emit loud sound on continuity mode for a distance.
-Built in camera, photo and movie viewer (again, skip the video stuff)
-Stability feature to alert if meter is accidentally knock over or moved.

These are just the top of my head. But you don't want to waste time making an inferior product only to be wipe out one or two years from now.






 

Offline MrPlacid

  • Frequent Contributor
  • **
  • Posts: 277
  • Country: us
  • Hobby Hobbyist
Re: Open Source Multimeter
« Reply #35 on: July 03, 2011, 03:38:32 am »
Battery life is very important in a hand held meter, beware.
Dave.

I agree. Rechargeable battery is a death wish. It means that meter will never last more than 20 year max. It'll be lucky to last 5-10 years. After that time, it tells everyone how crappy the hobby multimeter is that they all die out (went extinct!)
 

Offline House91320

  • Regular Contributor
  • *
  • Posts: 176
Re: Open Source Multimeter
« Reply #36 on: July 03, 2011, 03:54:16 am »
The battery is going to be user replaceable.
 

Offline MrPlacid

  • Frequent Contributor
  • **
  • Posts: 277
  • Country: us
  • Hobby Hobbyist
Re: Open Source Multimeter
« Reply #37 on: July 03, 2011, 04:19:51 am »
The battery is going to be user replaceable.

Is that particular battery a standard battery that will be in production x number of years from now? Plus, the multimeter will be out of work until the replacement battery is delivered. It needs to be easy as running to any local store to pick up some fresh batteries.

When you need the unit most and it's out of juice while on the field, we can't just say, "Today's work is cancel since my battery is dead. See you next week once the new battery arrived."
 

Offline Bored@Work

  • Super Contributor
  • ***
  • Posts: 3933
  • Country: 00
Re: Open Source Multimeter
« Reply #38 on: July 03, 2011, 08:14:28 am »
A DIY DVM kit is priced high than an equivalent fully assembled and warranted junk Chinese DVM.

Elenco kits are such an example. They resemble fully assembled meters but the kit costs four to five times as much as the assembled junk meter. E.g. compare the Elenco M-1007K with the iconic Chinese $5 junk meter incarnations, the 830th (e.g. DT830).
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

Online mikeselectricstuff

  • Super Contributor
  • ***
  • Posts: 12554
  • Country: gb
    • Mike's Electric Stuff
Re: Open Source Multimeter
« Reply #39 on: July 03, 2011, 10:09:25 am »
A feature which I've not seen on any sensible-cost meter, but which would be very cheap to implement is to be able to measure simultaneous DC voltage and current,  for efficiency testing voltage regulators.
I say DC as it gets much tricker at AC. For DC it's just a multiplexer.
PC software would allow connecting to two DMMs for direct readout of efficiency.
Quote
In response to usb isolation it its going to have some opto coupling for the data lines and I am going to use a transformer and dc to ac converter for the isolation of the power.
As regards optoisolation, you don't need a DC/DC converter as you will always have power available on the USB side. The method used my most meters today is probably the optimal one, i.e. the interface at the DMM is optical, and an external USB-optical link is used. This reduces the cost on the  DMM side for people who don't want it, and avoids issues of connectors that are vulnerable to moisture and damage.  Bandwidth is low so a simple LED/phototransistor provides a very low-cost solution.

Quote
tft color screen
Don't see the point in this ( apart from the 'gadget factor') as it will kill battery life. You just don't need colour on a DMM. What you do need is good visibility from no light to sunlight and long battery life

Getting an optimal display is a major challenge - a fully graphical display probably takes too much power, but an off-the-shelf fixed-segment one is not sufficiently flexible.
The ultimate answer is a custom segmented display with small matrix areas for units and function-key labels, but this means a couple of $K for LCD tooling. Unit cost is low after that though.
« Last Edit: July 03, 2011, 10:11:20 am by mikeselectricstuff »
Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
Day Job: Mostly LEDs
 

Offline Polossatik

  • Frequent Contributor
  • **
  • Posts: 295
  • Country: be
Re: Open Source Multimeter
« Reply #40 on: July 03, 2011, 10:24:40 am »

Quote
tft color screen
Don't see the point in this ( apart from the 'gadget factor') as it will kill battery life. You just don't need colour on a DMM. What you do need is good visibility from no light to sunlight and long battery life

Getting an optimal display is a major challenge - a fully graphical display probably takes too much power, but an off-the-shelf fixed-segment one is not sufficiently flexible.

+1

Colour lcd is just plain nonsense for a DMM seen you use a DMM not only on the bench but from the darkest corners up to full sunlight on a ladder .
Of course you might add a pixelQ screen to it, but that would be seriously overkill :)

I still use an old and silly (from specs perspective) vellman handheld scope for some stuff simply because it has a monochrome graphic lcd, hence you can use it in a lot of environments and actually *see* what is on the screen.


I would pay a premium to have an "up to date" mobile phone (so that you can use it as 3g BT modem for example) but with a non-color LCD screen that is actually readable outside like the old nokia 6310's .
well, now that's an idea :)
Real Circuit design time in minutes= (2 + Nscopes) Testim + (40 +120 Kbrewski) Nfriends

Testim = estimated time in minutes Nscopes= number of oscilloscopes present Kbrewski = linear approx of the nonlinear beer effect Nfriends = number of circuit design friends present
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #41 on: July 03, 2011, 11:00:52 am »
My video suggestion is rendering now as the next blog!
But here is the DaveCad sketch!

Dave.
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 2488
  • Country: us
Re: Open Source Multimeter
« Reply #42 on: July 03, 2011, 11:16:18 am »
Yeah, your open source multimeter must be completed with these feature:

Minimum, since these are already on the market:
-LCR

Great idea, I don't know how technically difficult it is to make a combined multi-meter and good LCR meter, but if possible it would be nice.

Quote
-Talking
-Dual trigger input like function to function as mini oscilloscope.

Do not want.  A strip-chart style display is the most "scope like" feature I need or want from a voltmeter, but I would rather have longer battery life from a non-graphic LCD.  Talking is just a silly gimmick 99% of the time.  Maybe it can be implemented in a useful way, but adding it as a bullet-point feature is just going to suck.

Quote
-luminosity
-audio meter
-Transmit wireless readings such as audio, video, photo, or just plain vanilla reading
-Built in camera, photo and movie viewer (again, skip the video stuff)
-Stability feature to alert if meter is accidentally knock over or moved.
-Timer, UP, Down, Clock, Alarm clock (Talking timer too)

If you can add some of these features without compromising cost, battery life, usability, or form factor maybe, but I wouldn't go overboard on the kitchen sink features.  Better to make a top notch meter and add features that support the basic usage.  Every feature you add is another position on the range switch, or another entry in a menu, and turning your meter into a full-fledged computer will do a number on battery life.  Important features for a meter are things like logging, storage, and USB/wireless links.  Maybe some more flexible audible alert: rather than a talking meter, how about one where you can set a threshold voltage (or other value) and it beeps when that level is exceeded?

One thing that might be nice for a rechargeable meter is one of those fancy near-field power links.  I don't know how well they work or how much interference they cause, but it would solve the isolation issues, and allow you to use the meter in 'logging' mode simply by resting it in a cradle.

It would be really nice if you could get a useful battery life out of 3 low-discharge AA NiMH batteries.  They are cheap, replacements will be widely available for decades, last a reasonable amount of time, and can be substituted with alkaline batteries in a pinch (make sure the charging circuit doesn't try to charge alkaline batteries).  Lithium ion batteries are lighter and higher capacity, but hard to find replacements for.
 

Online mikeselectricstuff

  • Super Contributor
  • ***
  • Posts: 12554
  • Country: gb
    • Mike's Electric Stuff
Re: Open Source Multimeter
« Reply #43 on: July 03, 2011, 12:08:14 pm »
I think you probably still want the range switch for everyday funcitons, so maybe it should have an 'other' position for fancy stuff and multi-channel functions...
Diode test should go to about 5V, and it should be able to do 4-wire ohms, with ohms-to-frequency audio tone for tracing shorts.

Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
Day Job: Mostly LEDs
 

Offline firewalker

  • Super Contributor
  • ***
  • Posts: 2397
  • Country: gr
Re: Open Source Multimeter
« Reply #44 on: July 03, 2011, 01:52:41 pm »
Maybe instruments design companies that watch this forum could contribute to the cause. I believe it would be an excellent use of social networks.

Alexander.
« Last Edit: July 03, 2011, 01:59:01 pm by firewalker »
Become a realist, stay a dreamer.

 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #45 on: July 03, 2011, 01:56:08 pm »


Dave.
 

Offline firewalker

  • Super Contributor
  • ***
  • Posts: 2397
  • Country: gr
Re: Open Source Multimeter
« Reply #46 on: July 03, 2011, 01:58:25 pm »
Just saw Dave's video. Really great IMHO. As an open source/hardware  it would probably need at least couple of years to hit the market.

Alexander.
Become a realist, stay a dreamer.

 

Offline Slobodan

  • Regular Contributor
  • *
  • !
  • Posts: 159
  • Country: cs
Re: Open Source Multimeter
« Reply #47 on: July 03, 2011, 02:55:02 pm »
@Dave

Nice video.
 

Online mikeselectricstuff

  • Super Contributor
  • ***
  • Posts: 12554
  • Country: gb
    • Mike's Electric Stuff
Re: Open Source Multimeter
« Reply #48 on: July 03, 2011, 03:21:29 pm »
My video suggestion is rendering now as the next blog!
But here is the DaveCad sketch!

Dave.
Thinking about it, you don't really need 4 isolated channels - for the majority of cases you only need 2 isolated channels, each doing V & I, as it will usually be possible to arrange a common point (even if it means readings are negative) . This would save a lot of cost for not much reduction in usefulness, as you need a whole front-end and behind each isolation barrier.
Also you could save more by having a 'primary' channel with all the component test stuff and a V/I channel, a secondary isolated V/I channels and isolation on the host interface.

For temperature, PT100/PT1000 would be good, and no additional hardware cost.

I'd prefer USB stick to SD, as all PCs have a USB interface but not all have an SD reader. 
However I think optoisolated serial with external USB converter gives you the most usefulness/cost ratio. Bluetooth is an option but a bit costly and power-hungry.

Another benefit of a USB host port is you could plug in a USB bluetooth stick when remote use is required.
« Last Edit: July 03, 2011, 03:31:07 pm by mikeselectricstuff »
Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
Day Job: Mostly LEDs
 

Offline Frant

  • Regular Contributor
  • *
  • Posts: 54
Re: Open Source Multimeter
« Reply #49 on: July 03, 2011, 04:21:55 pm »
@Dave

Great video! I really admire your enthusiasm!

About your suggestion to put four isolated channels... Yeah, that would be nice, but I don't really know of any isolation mechanism that could be used for this without wasting too much power for a battery powered meter. A separate ADC chip would be necessary for every channel. OK, there are low power high performance chips, such as AD779x, ADS124x or something like that, really nice. However, they would all need a dedicated isolated power supply, which is not so nice, and a separate SPI bus isolation, which is not nice at all.  Analog Devices iCoupler digital isolators with integrated isolated DC/DC converters may be used for this. However, just the mentioned parts are well over $100 already...

A modern reflective or "transflective" graphic LCD would not consume much power with the backlight off, probably 10 times less than the isolation of a single input channel.

The range switch can be replaced with software controlled relays as in bench multimeters, but that would significantly increase the overall power consumption. A combination of opto-MOS and bistable electromagnetic relays would probably be acceptable.

With all the input channels isolated and "floating", the controller side can be connected directly to a PC via the USB port. There is up to 500 mA available on a host USB port, which is more than enough for the whole thing. When using batteries, it would be essential to prevent the unused channels from drawing any supply current.
 

Offline ivan747

  • Super Contributor
  • ***
  • Posts: 2027
  • Country: us
Re: Open Source Multimeter
« Reply #50 on: July 03, 2011, 04:37:46 pm »
This is about Dave's multimeter:

Add math features, so you can do calculations with ANYTHING, including calculations of calculations. Example:
Input power = Vi*Ii
Output power = Vo*Io
Power loss = Input Power - Output Power

Percentage of power lost = (I can't remember and I can't figure it out on my mind without some paper and a calculator)

It needs a good labeling system though.

For Bluetooth / Zigbee / whatever you can use a removable module to save some money on the initial cost.
 

Offline hans

  • Super Contributor
  • ***
  • Posts: 1148
  • Country: nl
Re: Open Source Multimeter
« Reply #51 on: July 03, 2011, 04:52:12 pm »
If you power the thing from 4x 2500mAh AA batteries, in most ideal terms you can only draw 5mA @ 6V maximum to do a simple voltage measurement. So that's 30mW. It doesn't sound like a lot to me.
Of course this goes down FAST if you start to think about constant current sources, generators, quad channel, seperate temperature probes (probably requires seperate frontend), SD cards, dual screen (still draws more than a single screen!), etc.
I can imagine that isolation is quite hard to achieve that way. The hardware will get quite complex as in , analog frontend, display capability, automatic ranging, calibration, measurement stability (i.e. time/temperature drift or noise).

I think a quad channel accurate measurement device with all the protection circuitry is very hard to create, not even talking about batteries. Protection is a big issue because that kind of circuits use big components, which eats boardspace. Now, 4 fuses could be fitted into a device I'm sure, but you would need to have dual channel mob, power resistor and trace clearance taken into account. Powering the isolated circuit isn't an easy thing to do neither I can imagine.

I think it's better to have 2 devices with 1 V/I channel (that have seperated ground terminals) than 1 device with dual V/I channel. Possibly it would be nice to have a linking cable of some sort so you could link the multimeters together to have unique capabilities (you could transfer the data between devices to log multiple channels onto an SD card, or calculate effiency from figures taken on both meters). Isolating digital communication signals (RS485/RS232) is still a whole lot easier than designing an isolated DC/DC converter + digital isolation within 1 case.

Possibly , if you want a removable/external display module you could use RF to transport measurement data. This would be combined with the idea of having 2 meters linked together to do easy logging and efficiency calculations.

Another advantage with 2 meters is that you got 2 battery packs, like in you don't have to power all the features of quad channel from the same AA batteries.
« Last Edit: July 03, 2011, 04:54:55 pm by hans »
 

Offline Vertigo

  • Regular Contributor
  • *
  • Posts: 78
Re: Open Source Multimeter
« Reply #52 on: July 03, 2011, 06:28:48 pm »
This is about Dave's multimeter:

Add math features, so you can do calculations with ANYTHING, including calculations of calculations. Example:
Input power = Vi*Ii
Output power = Vo*Io
Power loss = Input Power - Output Power

Percentage of power lost = (I can't remember and I can't figure it out on my mind without some paper and a calculator)


now that sounds interesting :D
 

Alex

  • Guest
Re: Open Source Multimeter
« Reply #53 on: July 03, 2011, 06:32:02 pm »
Make sure this doesn't have the fate of Segway.
 

Offline ivan747

  • Super Contributor
  • ***
  • Posts: 2027
  • Country: us
Re: Open Source Multimeter
« Reply #54 on: July 03, 2011, 07:13:10 pm »

1. A modern reflective or "transflective" graphic LCD would not consume much power with the backlight off, probably 10 times less than the isolation of a single input channel.

2. The range switch can be replaced with software controlled relays as in bench multimeters, but that would significantly increase the overall power consumption. A combination of opto-MOS and bistable electromagnetic relays would probably be acceptable.

3. When using batteries, it would be essential to prevent the unused channels from drawing any supply current.

1. Maybe a variable frequency DC-DC converter could be used to reduce quiescent current.
2. I would like a slider switch. It is unnecessary for most of the channels because there's only one multifunction channel and it doesn't share the thermocouple input and it is auto-ranging (at least that's what I expect). For current there must be range sliders.
3. The microcontroller will take care of this. The will be lots of isolation. The opto-isolators should be off most of the time. Also please get some DC-DC converters with control inputs, not that 5 pin SOT-23 junk that doesn't even have an output disable pin nor a undervoltage protection function for the input voltage.
 

Offline DavidJRobertson

  • Regular Contributor
  • *
  • Posts: 51
  • Country: scotland
    • davidr.me
Re: Open Source Multimeter
« Reply #55 on: July 03, 2011, 07:48:20 pm »
This is about Dave's multimeter:

...

For Bluetooth / Zigbee / whatever you can use a removable module to save some money on the initial cost.

I'd recommend the RFM12B by HopeRF (http://www.hoperf.com/rf_fsk/cob/RFM12B.htm). They're low cost compared to ZigBee, at £6.17 individually from Farnell (UK), are available in smaller (Yet still easy to solder by hand; XBees are pretty large), more convenient SMD modules and, if I recall correctly, they consume less power. There's quite a lot of info about this module spread around this blog http://jeelabs.org/ (I'd recommend you take a read of this anyway, it's quite good).
 

Offline House91320

  • Regular Contributor
  • *
  • Posts: 176
Re: Open Source Multimeter
« Reply #56 on: July 03, 2011, 08:17:13 pm »
Cool vid Dave do you mind if use an develop on some of your ideas. Also do you know of a good place to get cheap lcds like the one in you micro watch but bigger.
« Last Edit: July 03, 2011, 08:21:21 pm by House91320 »
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #57 on: July 03, 2011, 10:35:04 pm »
Thinking about it, you don't really need 4 isolated channels - for the majority of cases you only need 2 isolated channels, each doing V & I, as it will usually be possible to arrange a common point (even if it means readings are negative)

There are problems with such a common ground terminal, as used on the Gossen. Watch my AA battery capacity tutorial for a practical demonstration of the problem.

Dave.
 

Offline nitro2k01

  • Frequent Contributor
  • **
  • Posts: 844
  • Country: 00
Re: Open Source Multimeter
« Reply #58 on: July 03, 2011, 10:35:47 pm »
Here my criticism of Dave's ideas. The few parts that are not just whining and complaining, but actual innovative ideas are bolded.
Quote
4 isolated channels (2xV, 2xI)
So my initial thought on Dave's idea is, four isolated channel seems a bit overkill. As Hans pointed out, what you really need most of the time is one or two V/I pairs for measuring power. And it also seems like you'd get a hard time getting the isolation done properly in that small space, even with two channels. How do you expect to power the second channel? Having a transformer for the power transfer seems like asking for interference problems, due to the AC needed to transfer the power. USB is easy in comparison since USB brings its own power. All you need is a simple USB controller and two optocouplers.
Quote
Output jack for programmable current, function generator or power supply
While this might be tempting to add to the current jack, is it really a good idea? As far as I understand, it's generally a good idea to keep the current circuitry as simple as possible to minimize the risk of failure. Like, only a low resistance shunt and a fuse. Switching the shunt seems like asking for long-term reliability issues.
Quote
SD card negates the need for USB...
Seems like a good idea at the surface, but does it really solve a problem? The destination is still the computer. You can do USB isolation on a whim. It also seems like the complexity of dealing with a memory card and file system would require a faster and more power-hungry microcontroller than you could get away with otherwise, unless you can live with slow transfer times. Taking the card in out of the unit is mechanically stressful to the card. Also, in terms of storage, do you really need that much space? It seems like a traditional interface (USB/IR) + something like a 1 MByte serial flash would do the job cheaper and better. The only time I could see you need that kind of logging space is if you're testing a lot of repetitive stuff, maybe on an assembly line or testing power/telephone stations in the field, or if you want to leave the thing on overnight probing something.
Quote
Bluetooth/Zigbee for wireless secondary display or PC/Phone interface
Again, bluetooth is a short distance protocol, and I doubt you'd get enough bang for the buck (power consumption in this case) compared to a more power-conservative wired interface. Then there's always the issue of interference. I could see the point for certain niche applications, and perhaps also for some people who want to show off, but for day-to-day work, I'm not too sure.
Quote
Two 5-digit displays for V/A/W/AC etc. Three would be nice, but adds complexity
Right on. I don't see how having three displays adds very much to the complexity compared to two, though. You'd still need to make a custom LCD panel, anyway. The number of segments should be the smallest issue. (Perhaps steal the Metrawatt layout, BTW, with one big and two small displays?)
Quote
Low power monographic display for whatever. Soft buttons, graph, etc...
Sure. However, I'm wondering if this is worth the complexity, unless you can fit onto the same glass as the digital display. (Novel idea, BTW: Ditch the LCD and go for an e-ink display...)
Quote
Does decent LCR/ESR
Power display/power factor
Sure.
Quote
Voice output
Eww! No! It would just sound tinny and you won't be able to hear what the bloody thing is saying. And besides, by the time the meter is done reading the numbers, the values will have changed. It's simply not an efficient way of conveying information. If we're talking novel ideas, one idea could be to use a tone to indicate the displayed value. Let's say it starts at 1 kHz. If you get a load spike, the pitch of the tone will go up. It won't tell you the exact value, but it will tell you in a very direct way that something is happening, and approximately what is happening.
Quote
Two/three temperature inputs.
Let me put it this way, if this was a commercial product, and this was not a feature that you wanted to use, you would complain about it. Also, putting any measuring points on the top of the device seems like a bad idea for signal integrity, since that's where you typically have all the digital stuff.
Quote
4xAA, aim for 500+ hours.
I think you were the one who complained that 4xAA multimeters typically couldn't measure the forward voltage of blue/white LEDs in diode mode...
« Last Edit: July 03, 2011, 10:40:22 pm by nitro2k01 »
Whoa! How the hell did Dave know that Bob is my uncle? Amazing!
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #59 on: July 03, 2011, 10:53:33 pm »
Ideas like the tones etc are a given. I deliberately did not go into detail on those types of features that are nothing more than simple software additions. It's a top level idea based around a floating multi channel concept.

Re. the number of common channels. As I said, go watch my AA battery capacity video where I demonstrate a real problem with the single ground System used on the Gossen Energy meter. Floating V and I inputs would fix that, or at least the jacks to allow kelvin measurement.

The AA's have nothing to do with diode test voltage. Most meters have the problem, yes, but only because the designers are lazy. You simply design in an appropriate converter to fix that.
The meter could be powered from a single AA and still have any test voltage you wanted.

Dave.
 

Offline House91320

  • Regular Contributor
  • *
  • Posts: 176
Re: Open Source Multimeter
« Reply #60 on: July 03, 2011, 10:56:09 pm »
Here is an early block diagram. also thinking of having little wireless bugs that you can measure voltage or current with an they would all transmit to the meter so you could petulantly read many different values at the same time wiresly.
« Last Edit: July 03, 2011, 10:59:40 pm by House91320 »
 

Offline nitro2k01

  • Frequent Contributor
  • **
  • Posts: 844
  • Country: 00
Re: Open Source Multimeter
« Reply #61 on: July 03, 2011, 11:23:06 pm »
Re. the number of common channels. As I said, go watch my AA battery capacity video where I demonstrate a real problem with the single ground System used on the Gossen Energy meter. Floating V and I inputs would fix that, or at least the jacks to allow kelvin measurement.
I see your point, however you don't really need true galvanic isolation in that case. You just need current measurement plus a two-terminal differential input with neither of the inputs shorted to ground. Of course that's just bickering about the exact definition of isolated more than anything else.
The AA's have nothing to do with diode test voltage. Most meters have the problem, yes, but only because the designers are lazy. You simply design in an appropriate converter to fix that.
The meter could be powered from a single AA and still have any test voltage you wanted.
Of course you can boost the voltage all you want, but then you need to consider things like the power consumption of the converter itself, and the noise it introduces. That's just design decisions, but I suspect that it would be easier to use a 9V battery.
Whoa! How the hell did Dave know that Bob is my uncle? Amazing!
 

Offline DavidJRobertson

  • Regular Contributor
  • *
  • Posts: 51
  • Country: scotland
    • davidr.me
Re: Open Source Multimeter
« Reply #62 on: July 03, 2011, 11:27:27 pm »
Ugh. 9V PP3 batteries are awful...
 

Offline zunklimt

  • Newbie
  • Posts: 3
Re: Open Source Multimeter
« Reply #63 on: July 04, 2011, 12:00:06 am »
Hello to all !

I'm happy to finally join this forum after a long time just watching all the very fine Dave's videos

I love the idea of an open source multimeter !

So I've made a little drawing with how I see the think

It's still just a first draft, there are lots of details to be adjusted/corrected but here it is by now:

- ONE SINGLE BIG SCREEN (E-INK or OLED)
- USB or WIFI or BLUETHOTH to configure the meter from a computer and for realtime readings on a PC
- NO VOICE (numbers are universal, a voice solution would require to think about what languages to use)
- USER CONFIGURABLE SCREEN DESIGN AND FUNCTIONALITIES

i've included two versions of the idea: one with the connection at the bottom like standard, another with the connection over the screen to keep all the cables away when using on a flat surface (though if used vertically, the classic disposition is better)

i hope you like it

ZundKlimt


« Last Edit: July 04, 2011, 12:05:54 am by zunklimt »
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #64 on: July 04, 2011, 12:07:15 am »
Of course you can boost the voltage all you want, but then you need to consider things like the power consumption of the converter itself, and the noise it introduces. That's just design decisions, but I suspect that it would be easier to use a 9V battery.

The converter would only switch on when required, so power consumption is not an issue.
Noise, well, you design it so it doesn't interfere  ;D

A 9V battery would be suicide for a meter of this complexity. Not nearly enough capacity. The AA's will struggle, power management would have to be aggressive.

Dave.
 

Offline zunklimt

  • Newbie
  • Posts: 3
Re: Open Source Multimeter
« Reply #65 on: July 04, 2011, 01:46:09 am »
here is a second version of my drawing, this time i separated the connections from the controls and screen into two separated type of boxes

All the necessary electronics and protection circuits are located inside the small CONNECTION BOXES which should be as flat as possible.


Each connector can be freely configured as an iput or as an output and several readings can be made simultaneously at each connection.
(of course, here i don't take in consideration how possible or not this would be in terms of electronic circuitry, this is just an idealized wish...

INPUTS: V, mA, Watt, Capacitance, Freq, Temp, Etc...
OUTPUTS; dcV+mA or WAVEFORM+FREQ+AMPLITUDE or TRIGGER or Etc...

All the data is transmited via WIFI or USB between the CONNECTION BOXES and a dedicated CONTROL UNIT (including a big E-INK/OLED screen and soft buttons) or to a SMARTPHONE or to a COMPUTER

several CONNECTION BOXES could be used with one single computer to get more channels of I/Os

with this equipment there would not be much diference between a multimeter, an osciloscope, a function generator or a power supply... this would be all in one ...

well, i'll keep dreaming...



« Last Edit: July 04, 2011, 01:47:42 am by zunklimt »
 

Offline s_lannan

  • Contributor
  • Posts: 28
  • Country: au
Re: Open Source Multimeter
« Reply #66 on: July 04, 2011, 02:22:26 am »
put a capacitor ESR meter in it...
 

Offline Tony R

  • Regular Contributor
  • *
  • Posts: 117
  • Country: 00
Re: Open Source Multimeter
« Reply #67 on: July 04, 2011, 02:34:19 am »
Ok - The first couple pages of this thread makes me a little upset to see people are thinking an open source project must be cost effective. To cite the most well known and well used open source project out there, Linus Torvalds did not want to make his operating system profitable or economical, he just wanted an OS that worked the way HE wanted it to. Who says it needs to be a competitor, that's one thing I don't like about the engineering type (Which, at times, includes myself.) Linus Torvalds had no idea his OS would run on many many servers and computers, nor did he know it would be the OS of 459 of the top 500 super computers in late 2010 (which is over 90%.)

My point is do not end this now, because who knows what it will become! Engineers tend to think "Is it worth doing? can I get the same thing somewhere else?" Yes, there are 1000s of different kinds of multimeter for all different markets. I can not argue with the fact that yes, it will cost more to make one then it will be to buy one. But Linus could have just got an OS and ran it instead of creating his own OS UNIX would have worked fine for him.

With all that said, here is what i think the multimeter should be sure to have...
*Rechargeable battery is nice
*Data Logging (sd card)
*A alarm - say voltage gets over or under a center value have it make a noise
*Screw USB, Bluetooth would be nice, you can also avoid isolation this way.
*I like the idea of having the standard thermocouple input, maybe have 2 (like dave came up with)
*Of course a diode tester, one that can go beyond 3V
*LSR meter
*High Voltage sound, make a noise when the voltage goes above 90V (or whatever is though necessary)
*I would like computer software that makes it easy to interface with MatLab
*I would also like to see a DMM with no rotary switch, so if it could be all push buttons i think that would be a unique design.

Tony R.
Computer Engineering Student
Focus: Embedded Assembly Programming, Realtime Systems,  IEEE Student Member
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #68 on: July 04, 2011, 03:06:12 am »
Ok - The first couple pages of this thread makes me a little upset to see people are thinking an open source project must be cost effective. To cite the most well known and well used open source project out there, Linus Torvalds did not want to make his operating system profitable or economical, he just wanted an OS that worked the way HE wanted it to. Who says it needs to be a competitor, that's one thing I don't like about the engineering type (Which, at times, includes myself.) Linus Torvalds had no idea his OS would run on many many servers and computers, nor did he know it would be the OS of 459 of the top 500 super computers in late 2010 (which is over 90%.)

Linus Torvalds never made hardware. He did not have to care about how much something cost, or how expensive or difficult it was to manufacture, or if you could get the parts etc.

Cost must be considered in OSHW projects or else they the concept will fail because no one will ever build anything.
The goal of OSHW projects is usually to encourage other people to build one too, and that often means custom parts like PCB's, cases etc must be made readily available. That won't happen if it's not cost effective.
If your goal is to produce one unit, and not have anyone else ever build one, and just share the design info, then fine, but that's usually not the reason people do major OSHW projects like this.

Dave.
 

Offline Zad

  • Super Contributor
  • ***
  • Posts: 1013
  • Country: gb
    • Digital Wizardry, Analogue Alchemy, Software Sorcery
Re: Open Source Multimeter
« Reply #69 on: July 04, 2011, 03:54:15 am »
Okay. Well, my first reaction is: Nope, not gonna happen. Seen it a thousand times before, mostly in my own notebooks. A product with lots of enthusiasm, but some huge flaws.

Sanity check!

Try and get a ballpark quote for the custom enclosure. Chances are that it is going to cost more than the price of the house you live in, and certainly more than the cost of the electronics. I seem to remember that tooling for the TV-B-Gone was well over $10,000, and that is a pretty simple and small case. While you are at it, try and get a quote for custom  LCDs. Now realise how attractive those dot matrix greyscale trans/flective LCDs look. E-paper is currently way too hard to get hold of and has an awfully slow update rate. OLED looks sexy, but power consumption is going to be a killer in this application.

So, having got the grumpy realities out of the way, what next? Well, the engineers most familiar enemy is among us: Creeping Featurage. That temptation to add more and more and more stuff, just because you can. Still, nobody is going to buy a standard A-V-O meter for $200 when they can buy one which is better for $50, so it needs extra features.

Personally, I would forget about it being a hand held multimeter and go for a bench meter. Appropriate enclosures are much easier to buy (and fabricate) for bench equipment. If the problem you are dealing with is *that* difficult that it requires such a fancy meter, then you are going to be at your bench, not in the field.  To get even half of the features mentioned into a hand portable case is going to be impossible, even for commercial production density.

Having 4 channels alone is going to need considerable space, and to retain isolation it will need quite meaty relays for some range selection. 4 properly isolated channels with good resolution in a small space isn't easy. If you are still determined to go hand-held then consider slim high-density mobile phone batteries as an alternative to 4xAA cells. Mini-USB connection would be ideal for charging, as this would allow the use of any modern mobile phone charger. Galvanic isolation is quite easy.

Why not use the standard channels in voltage configuration for temperature sensing?

Using an Amps/Volts input socket for power supply / signal generation is going to run the risk of connecting it to a live mains potential (if inadvertently selected). I would feel nervous with 4 potentially mains level (or even low voltage 10A) connections physically so close to each other on a hand held device.  Maybe have a secondary 2 channel V/A measurement remote headless slave unit?

I would have 3 additional (or 4 if we are going for Kelvin sensing $$$) terminals for component testing, which also function as a signal generator (easy to do with a cheap DDS+buffer) and power supply. This physically separates it from the V/A, primarily for safety reasons, but it also disconnects a lot of hardware from the LCR sensing system. You want as little capacitance and inductance on the LCR measurement terminal as possible if you are going to get reasonable resolution and range. Yes, this would remove resistance sensing from the standard measurement terminals but increases precision considerably. Maybe add a separate low resolution resistance measurement? In my experience you rarely need to do precision component characterisation when you are doing mostly V/A work.

SD-Card. I think having an SD card socket in the case is a BAD idea (so bad that I put it in capitals). Even when populated, that slot is going to be an entry point for dust, moisture, bits of solder, you name it. If it were a commercial design, I would make it accessible under the battery cover. As an Open Source design intended for 1-off and small runs, I would mount it on the main PCB.

I don't think I would trust touch-buttons to have sufficient isolation for mains measurement. Even if the ADC modules are correctly isolated (and let us not for get this is open source, people may cut corners!) then something in my caveman survival instincts tells me not to touch even insulated metal pads. Conventional tactile pushbuttons are much more reassuring but still need ingress prevention via a shaped neoprene (or similar) button mat. A bench meter would have panel space for a rotary input device and 2 separate graphical displays.

Sound generation is easy on a controller like a Cortex M3 with 512MB of onboard flash. If speech isn't used, audible cues are still very handy. With regard to remote access, I would prefer WiFi to Bluetooth / ZigBee. That way, it is possible to use your mobile phone or ipod touch etc to view web pages generated on the fly, without and application software. With an appropriate router you could (e.g.) monitor experiments at work from home, on holiday etc.

So, my advice would be that if you want it all-singing all-dancing, go with a bench meter, with more room for isolated high-res low-noise ADCs in multiple channels. Power isn't a problem then, and you can use colour LCD panels. Measurement of mains level voltages and high currents can be done with remote head units.

If you go with hand-held, then stick to 2 (isolated) channels with what is effectively a separate LCR meter and component analyser (2-terminal diode, 3-terminal transistor and regulator). Design an external display-less 2-channel unit for measuring 2nd and subsequent ports.

One more thing. How about proper low-current measurement with a transimpedance amplifier? I think you could make a very average meter, but with  zero-burden microcurrent measurement you would have a product with a distinct Unique Selling Point, which is what marketers love!


Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #70 on: July 04, 2011, 04:33:52 am »
Okay. Well, my first reaction is: Nope, not gonna happen. Seen it a thousand times before, mostly in my own notebooks. A product with lots of enthusiasm, but some huge flaws.

I agree. Doesn't mean it's not fun to toss around ideas  ;D

Quote
Try and get a ballpark quote for the custom enclosure. Chances are that it is going to cost more than the price of the house you live in, and certainly more than the cost of the electronics. I seem to remember that tooling for the TV-B-Gone was well over $10,000

IIRC he paid $30K up front before the first unit rolled off the production line.
And that's a project with an 8 pin PIC, a battery, one switch, and an IR LED.
He went nuts though, could have done it for MUCH less than that.

Quote
Personally, I would forget about it being a hand held multimeter and go for a bench meter. Appropriate enclosures are much easier to buy (and fabricate) for bench equipment.

I agree. A bench meter with an off-the-shelf enclosure stand much better chance of success. There is a thread on that for the open hardware bench meter some time back.

Quote
Why not use the standard channels in voltage configuration for temperature sensing?

Simple. Then you lose the voltage channels for logging. The whole idea is being able to log voltages, currents, and temp at the same time.

Quote
SD-Card. I think having an SD card socket in the case is a BAD idea (so bad that I put it in capitals). Even when populated, that slot is going to be an entry point for dust, moisture, bits of solder, you name it. If it were a commercial design, I would make it accessible under the battery cover. As an Open Source design intended for 1-off and small runs, I would mount it on the main PCB.

Yes, it needs finer details sorted. There are several ways to make it work. So if you want an SD card in the meter, you can make it happen.

Quote
One more thing. How about proper low-current measurement with a transimpedance amplifier? I think you could make a very average meter, but with  zero-burden microcurrent measurement you would have a product with a distinct Unique Selling Point, which is what marketers love!

Yes, that's a given I would have thought.

Dave.
 

Offline Bored@Work

  • Super Contributor
  • ***
  • Posts: 3933
  • Country: 00
Re: Open Source Multimeter
« Reply #71 on: July 04, 2011, 06:19:09 am »
Ok - The first couple pages of this thread makes me a little upset to see people are thinking an open source project must be cost effective.

You conveniently forgot to mention that the one asking the original question mentioned this is for a kickstarter project. If you don't know kickstarter, it is a web site where people are collecting funding for their projects. This project is right from the start business, not hobby. He just chose to make the project more interesting by labeling it open source.
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 2488
  • Country: us
Re: Open Source Multimeter
« Reply #72 on: July 04, 2011, 07:46:41 am »
Hmm.... it just occurred to me that there is a potential issue with having the amps channel isolated from the voltage channel.  It makes AC power considerably more complicated.  To measure AC power you need to multiply the instantaneous voltage and current.  In a non-isolated power meter you can use an analog multiplier followed by a standard sigma-delta or dual-slope ADC.  The alternative is to digitize the I and V waveforms at high speed and  multiply in software.  This costs a bit more power both for the ADC and the CPU, but is still easy to do by using a dual-channel ADC so the I and V are automatically synchronized.  The advantage of this is that you only need 2 ADCs and you can get everything in software: DC+AC volts  / DC+AC amps / power / apparent power / crest factor / phase lag.  With the analog multiplier, you need 3 ADCs and you don't get crest factor, phase angle, or separate DC+AC components without extra hardware.

With true isolation you either need to transfer the analog signal over the isolation barrier or have a common (opto-isoated) clock and transmit the 'high bandwidth' digital signal over the link.  I would probably go the first route -- the current input module would have only the range switching logic and a linear opto-coupler.  The voltage measurement module would have ADCs for both channels.  I would still go with the high speed digitizing approach and compute RMS and power in software because it is more flexible and powerful and you can display the waveforms if you want.
 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #73 on: July 04, 2011, 08:44:40 am »
Ok - The first couple pages of this thread makes me a little upset to see people are thinking an open source project must be cost effective. To cite the most well known and well used open source project out there, Linus Torvalds did not want to make his operating system profitable or economical, he just wanted an OS that worked the way HE wanted it to. Who says it needs to be a competitor, that's one thing I don't like about the engineering type (Which, at times, includes myself.) Linus Torvalds had no idea his OS would run on many many servers and computers, nor did he know it would be the OS of 459 of the top 500 super computers in late 2010 (which is over 90%.)

My point is do not end this now, because who knows what it will become! Engineers tend to think "Is it worth doing? can I get the same thing somewhere else?" Yes, there are 1000s of different kinds of multimeter for all different markets. I can not argue with the fact that yes, it will cost more to make one then it will be to buy one. But Linus could have just got an OS and ran it instead of creating his own OS UNIX would have worked fine for him.

With all that said, here is what i think the multimeter should be sure to have...
*Rechargeable battery is nice
*Data Logging (sd card)
*A alarm - say voltage gets over or under a center value have it make a noise
*Screw USB, Bluetooth would be nice, you can also avoid isolation this way.
*I like the idea of having the standard thermocouple input, maybe have 2 (like dave came up with)
*Of course a diode tester, one that can go beyond 3V
*LSR meter
*High Voltage sound, make a noise when the voltage goes above 90V (or whatever is though necessary)
*I would like computer software that makes it easy to interface with MatLab
*I would also like to see a DMM with no rotary switch, so if it could be all push buttons i think that would be a unique design.
Didn't the OP say it was a Kickstarter project? By definition this means it MUST be cost effective, otherwise who is going to pony up for it?
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

Online mikeselectricstuff

  • Super Contributor
  • ***
  • Posts: 12554
  • Country: gb
    • Mike's Electric Stuff
Re: Open Source Multimeter
« Reply #74 on: July 04, 2011, 10:40:26 am »
Didn't the OP say it was a Kickstarter project? By definition this means it MUST be cost effective, otherwise who is going to pony up for it?
That assumes the project creators have a realistic idea of costs.
I always wondered what happens with a kickstarter when the money raised ends up not covering costs due to unforseen issues...
Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
Day Job: Mostly LEDs
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #75 on: July 04, 2011, 11:51:49 am »
That assumes the project creators have a realistic idea of costs.
I always wondered what happens with a kickstarter when the money raised ends up not covering costs due to unforseen issues...

Interesting question.
AFAIK, once the project reaches it's goal, the project automatically gets the money in the bank, with potentially no recourse for the donators if you don't deliver?
Surely it's happened, anyone know?

Dave.
 

Offline ruku

  • Contributor
  • Posts: 25
Re: Open Source Multimeter
« Reply #76 on: July 04, 2011, 03:21:38 pm »
Wow, this thread has totally taken off. I had my reserves the other week when I looked at it, and thought... meh! Idealistic, not going to fly too far.

While I think that the "how will people buy this" thing might be an issue, I'd TOTALLY get involved in this project, if only to learn as much as I can!

Dave, I really think there'd be some merit to bringing in the forum members here to design a project together. As long as you can assign people to help moderate and finalize decisions (so we're not stuck in analysis paralysis forever), I think it'd totally be awesome to run the gamut of the engineering V and design something!
 

Offline KuchateK

  • Regular Contributor
  • *
  • Posts: 78
  • Country: us
Re: Open Source Multimeter
« Reply #77 on: July 04, 2011, 06:00:44 pm »
Someone mentioned to make it bench multimeter. I think it would be much better idea.

You can use big components with loose PCB spacing and have it servicable at home. Proper input protection with nice blast shields can be made at home. You don't have to worry about AA or 9V batteries. Bench case is so big you can put there 12v ups battery and still would be portable.

For the display... please don't listen to Dave (no offence) ;)

Just put the biggest mono (no color!) graphical LCD screen with backlight. Then you can display single, dual, triple, quadruple or even more channels in different layouts. You can have graphs and bargraphs. Display ton of text for help and schematics how to connect probes. This will give ton of flexibility including different fonts, symbols and anything you can imagine.

Look how nice Agilent meters with OLED displays are. Or better. Check out Fluke 287 & 289!
http://www.fluke.com/fluke/usen/digital-multimeters/fluke-289.htm?PID=56061&trck=289specifications

By having dual 5 digit displays you will lock yourself to have stupid loops of "press to display channel #x". Then second display for menus... Its complicated even before it started... Lets drop that gazzilion year fixed display technology.

Edit: Dave did review of Fluke:
« Last Edit: July 04, 2011, 07:18:16 pm by KuchateK »
 

Offline ndictu

  • Regular Contributor
  • *
  • Posts: 210
  • Country: sk
Re: Open Source Multimeter
« Reply #78 on: July 04, 2011, 06:36:16 pm »
Someone mentioned to make it bench multimeter. I think it would be much better idea.

You can use big components with loose PCB spacing and have it servicable at home. Proper input protection with nice blast shields can be made at home. You don't have to worry about AA or 9V batteries. Bench case is so big you can put there 12v ups battery and still would be portable.

For the display... please don't listen to Dave (no offence) ;)

Just put the biggest mono (no color!) graphical LCD screen with backlight. Then you can display single, dual, triple, quadruple or even more channels in different layouts. You can have graphs and bargraphs. Display ton of text for help and schematics how to connect probes. This will give ton of flexibility including different fonts, symbols and anything you can imagine. Look how nice Agilent meters with OLED displays are.

I agree. Once you go for bench design there is no need to conserve power so just put whatever display there you can find and then you can do all sorts of stuff with it.

Also, since it's opensource it should be really easy to build at home. There can be a professional design with SMD parts and multilayer PCBs but also a bigger double-sided through hole one (since the schematic would be open I'm sure someone would redesign it). Everyone could either purchase a kit or make their own PCB, buy the parts, make changes to hardware and firmware and build their own custom version.
 

Offline KuchateK

  • Regular Contributor
  • *
  • Posts: 78
  • Country: us
Re: Open Source Multimeter
« Reply #79 on: July 04, 2011, 08:45:18 pm »
I forgot to mention. Bench instrument cases are available off the shelf, so only front/back panels must be custom.

Today it may be easier to get color LCD, so we might be forced to swallow that extra power usage.
 

Offline Bored@Work

  • Super Contributor
  • ***
  • Posts: 3933
  • Country: 00
Re: Open Source Multimeter
« Reply #80 on: July 04, 2011, 10:00:20 pm »
I forgot to mention. Bench instrument cases are available off the shelf

Many are. But interestingly I never found a source offering my favorite bench instrument form factor, complete with a handle and rubber bumpers 254 x 104 x (303 ... 375) mm^3 stackable. Companies like Agilent use them for ages for smaller instruments. E.g. http://www.home.agilent.com/agilent/product.jspx?nid=-536902257.536881980.00

If someone has a source for these specific enclosures I would be glad to hear of it.
« Last Edit: July 04, 2011, 10:04:06 pm by BoredAtWork »
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

Offline Frant

  • Regular Contributor
  • *
  • Posts: 54
Re: Open Source Multimeter
« Reply #81 on: July 04, 2011, 10:39:26 pm »
Someone mentioned to make it bench multimeter. I think it would be much better idea.

Just put the biggest mono (no color!) graphical LCD screen with backlight. Then you can display single, dual, triple, quadruple or even more channels in different layouts. You can have graphs and bargraphs. Display ton of text for help and schematics how to connect probes. This will give ton of flexibility including different fonts, symbols and anything you can imagine.

I mentioned a bench meter, but I also said it could be a modular system. It's an open source project and people would like to make different modules to suit their needs, to add channels, to upgrade existing modules and to learn something in the process. It should be an open hardware and software platform rather than a fixed hardware design. Professional modular instrument platforms exist, and I mentioned two: PXI and Agilent USB Modular Instruments. However, this open source project should be much cheaper to build and also simple enough to be accepted by hobbyists.

As for the display, it can be a part of an user interface module, so that one can choose from several options or not to have it at all. It's a bench instrument and there would probably be a PC on the same bench, with much more user interface resources.

USB is a good choice because it is fast and it provides up to 500 mA for the instrument, so the mains power supply may not be needed. I'm not so enthusiastic about wireless things in situations where they are not absolutely necessary. They are inherently less reliable, they add complexity to the system and always involve batteries which must be taken care of. However, I had a surprisingly good experience with a SENA Parani-ESD200 Bluetooth-serial module, used with a Bluetooth/USB adapter connected to a PC. Once set properly, it worked flawlessly for months. It was actually used to isolate a sensitive signal acquisition system from a PC.
 

Offline ndictu

  • Regular Contributor
  • *
  • Posts: 210
  • Country: sk
Re: Open Source Multimeter
« Reply #82 on: July 04, 2011, 11:00:55 pm »
I mentioned a bench meter, but I also said it could be a modular system. It's an open source project and people would like to make different modules to suit their needs, to add channels, to upgrade existing modules and to learn something in the process. It should be an open hardware and software platform rather than a fixed hardware design. Professional modular instrument platforms exist, and I mentioned two: PXI and Agilent USB Modular Instruments. However, this open source project should be much cheaper to build and also simple enough to be accepted by hobbyists.

As for the display, it can be a part of an user interface module, so that one can choose from several options or not to have it at all. It's a bench instrument and there would probably be a PC on the same bench, with much more user interface resources.

Exactly. For example, I would like to start with a simple two channel input interface, with V/ohm and current, and an USB interface with the display/data logging on the PC. Then later get some display, add some button interface and have a more stand-alone unit. Someone might want to add a big flash for data logging, someone will just leave the PC running for that. Someone wants a lot of current inputs, someone will put on 10 thermocouple inputs.

Something like a modular reference design and everyone can make little changes, pick what they like, ignore the rest or add it later.
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #83 on: July 05, 2011, 02:50:07 am »
You can use big components with loose PCB spacing and have it servicable at home. Proper input protection with nice blast shields can be made at home. You don't have to worry about AA or 9V batteries. Bench case is so big you can put there 12v ups battery and still would be portable.

For the display... please don't listen to Dave (no offence) ;)

Just put the biggest mono (no color!) graphical LCD screen with backlight. Then you can display single, dual, triple, quadruple or even more channels in different layouts. You can have graphs and bargraphs. Display ton of text for help and schematics how to connect probes. This will give ton of flexibility including different fonts, symbols and anything you can imagine. Look how nice Agilent meters with OLED displays are.

I agree. Once you go for bench design there is no need to conserve power so just put whatever display there you can find and then you can do all sorts of stuff with it.
[/quote]

I disagree on not conserving battery power. I'd still want a bench meter say D cell powered. (please, forget this rechargable rubbish!)
With D cells you could possibly create a killer battery life logging meter, opening up new niche markets.

7 segment LCD's still kill dot matrix for viewability, sorry, no contest. Having both is not such a stupid idea, and can help when you go into long term data log battery mode to conserve power yet still display status.

Dave.
 

Offline thmjpr

  • Regular Contributor
  • *
  • Posts: 160
  • Country: ca
Re: Open Source Multimeter
« Reply #84 on: July 05, 2011, 04:03:52 am »
Interesting question.
AFAIK, once the project reaches it's goal, the project automatically gets the money in the bank, with potentially no recourse for the donators if you don't deliver?
Surely it's happened, anyone know?

Dave.

Quote
There is no guarantee that people that post projects on Kickstarter will deliver on their projects or use the money to do their projects. Kickstarter advises sponsors to use their own judgment on supporting a project. They also warn project leaders that they could be liable for legal damages from sponsors for failure to deliver on promises. In May 2011 a New York University film student raised $1,726 to make a film, but plagiarized the French film Replay instead.
from http://en.wikipedia.org/wiki/Kickstarter
 

Offline fchk

  • Regular Contributor
  • *
  • Posts: 108
  • Country: de
Re: Open Source Multimeter
« Reply #85 on: July 05, 2011, 09:49:30 am »
I've just seen the video and really like the idea of multiple inputs.

However, I'm a very big fan of the UNIX philosophy: have small, single-purpose tools that do their things right. The video suggests some kind of feature-itis, which definitely will make the whole thing more expensive, but not neccessarily better. If I need temperatures, I'll get a thermometer. If I need to measure impedances, I take a decent RCL meter, which only does this single task, but is way superior in terms of accuracy compared to most general purpose meters. Having a single-purpose Volts-Amps-Watts-Wh meter would make the input circuits much easier and propably more precise.

One or two CV/CC outputs might make sense for some tasks, but this could easily be added as an second step.

For the display nothing beats VFD's in terms of readability. I really like my Agilent 34401A
 

Offline ndictu

  • Regular Contributor
  • *
  • Posts: 210
  • Country: sk
Re: Open Source Multimeter
« Reply #86 on: July 05, 2011, 11:55:47 am »
7 segment LCD's still kill dot matrix for viewability, sorry, no contest. Having both is not such a stupid idea, and can help when you go into long term data log battery mode to conserve power yet still display status.

Well, once again, with the bench design

- you have much more space, so why not. You could have one, two or three standard 7segments and one dotmatrix for menus, or extra measurements if you don't have enough 7segments.

- everyone can build their own version. Someone prefers 7segments, someone wants a big dotmatrix.

About the batteries, do you mean a battery powered or as a backup? Maybe while running on mains you could be using everything but when you disconnect it (or power goes out) it'll try to conserve power by switching displays off?
 

Offline Bloch

  • Supporter
  • ****
  • Posts: 444
  • Country: dk
Re: Open Source Multimeter
« Reply #87 on: July 05, 2011, 07:27:46 pm »
Many are. But interestingly I never found a source offering my favorite bench instrument form factor, complete with a handle and rubber bumpers 254 x 104 x (303 ... 375) mm^3 stackable.

That about Bopla BOTEGO

240,98 mm * ( 49,96 mm, 65,20 mm, 80,44 mm) * 196,9 mm
307,35 mm * ( 49,96 mm, 65,20 mm, 80,44 mm) * 196,9 mm

stackable , handle  as option
and a  angled operating front is an option

http://www.bopla.de/en/product-catalog/enclosure-technology/product-category/botego-6.html


 

Offline Bloch

  • Supporter
  • ****
  • Posts: 444
  • Country: dk
Re: Open Source Multimeter
« Reply #88 on: July 05, 2011, 07:50:02 pm »
With D cells you could possibly create a killer battery life logging meter, opening up new niche markets.

Now that is some thing I like  ;D

I did a quick look in a catalog Varta batteries

AAA HIGH ENERGY  1,1Ah LR03 1200mAh
AA  HIGH ENERGY  2,6Ah LR06 2930mAh
C   HIGH ENERGY  7,8Ah LR14 7800mAh
D   HIGH ENERGY 16,5Ah LR20 16500mAh


No. Now I think about it. It is just to much power  :)




 

alm

  • Guest
Re: Open Source Multimeter
« Reply #89 on: July 05, 2011, 10:12:34 pm »
For the display nothing beats VFD's in terms of readability. I really like my Agilent 34401A
7-segment LED comes close, often superior since the digits tend to be larger. Of course they don't do text well. LCD sucks for bench use in my opinion, VFD and LED are just superior for displaying numbers if you don't care about power use. Viewing angle is important if you don't want to move equipment all the time.
 

Offline Kiriakos-GR

  • Super Contributor
  • ***
  • !
  • Posts: 3525
  • Country: gr
  • User is banned.
    • Honda AX-1 rebuild
Re: Open Source Multimeter
« Reply #90 on: July 06, 2011, 12:07:03 am »
so please stop posting nonsense like all this...

Forum rule No1 ,  never say to others what to say or not.
If you can not handle the conversation, ignore it.   

Just a friendly advice.
« Last Edit: July 06, 2011, 12:10:50 am by Kiriakos-GR »
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #91 on: July 06, 2011, 12:14:43 am »
Quickest sketch took me 20 min...

Wow, Awesome!

Dave.
 

Offline Zad

  • Super Contributor
  • ***
  • Posts: 1013
  • Country: gb
    • Digital Wizardry, Analogue Alchemy, Software Sorcery
Re: Open Source Multimeter
« Reply #92 on: July 06, 2011, 01:10:52 am »
Blimey!!!!! I don't agree with ANYTHING that you've posted, not a single point! What a lot of rubbish! I am not going to spend any more time on this, but just to say that a decent prototype case for this type of enclosure (about 5 units) will take for about $300, so please stop posting nonsense like all this...

Robust peer review is the basis of all sound science, but denial without explanation is simply Trolling, and is the curse of many forums around the Internet. Anyone can say "No, you are wrong", but it takes skill and intelligence to say why.

If you care to read my post instead of jumping to conclusions, you will notice I talk about tooling (i.e. for production) not 1-off prototype enclosures. Prototypes can be milled from solid or built up using desktop prototyping methods, this is clearly not viable for production quantities.



Anyway, so I don't create an entirely negative post, 256x64 monochrome OLED displays are getting quite cheap now. Crystalfontz retail them in 1000+ qty for $23:48 ($51:48 1-off). They have on-board controllers and 16 level grey-scale.
http://www.crystalfontz.com/product/CFAL25664AYB1

If the designer should choose to go with a bench instrument (or a big battery) Crystalfontz also do 320x240xRGB TFT with integrated controller for $18:82 in 1000+ qty. ($53.72 in 1-off) It also has a touch screen option.
http://www.crystalfontz.com/product/CFAF320240F-035T

That seems phenomenally cheap for a QVGA including controller, where is the gotcha? I designed some bench test equipment about 7-8 years ago, and the display+controller came in at around £250 (100-ish qty) for a similar QVGA.


Offline Tony R

  • Regular Contributor
  • *
  • Posts: 117
  • Country: 00
Re: Open Source Multimeter
« Reply #93 on: July 06, 2011, 02:31:34 am »

Linus Torvalds never made hardware. He did not have to care about how much something cost, or how expensive or difficult it was to manufacture, or if you could get the parts etc.

Very true; however, and perhaps I should have stated it more clearly, if someone wants to make their own DMM and publish everything as to how they did it, and maybe someone else will take that design and improve upon it, why not do it? Maybe it wont be very popular, but who says it has to be?

Tony R.
Computer Engineering Student
Focus: Embedded Assembly Programming, Realtime Systems,  IEEE Student Member
 

Offline Bloch

  • Supporter
  • ****
  • Posts: 444
  • Country: dk
Re: Open Source Multimeter
« Reply #94 on: July 06, 2011, 05:30:44 am »
Display.

If it is a "long time" product. I mean a  product that will be interesting many years. Then I dont like LCD + oled .......

I think it will be a bad choice to use a part that will not be on sale in like 3 years.

But with Led´s I dont think they will go away for the next 10 years.


Iphone app.

This is also a bad choice.

It is a "lock in" Can the app run i the old Iphone or the next one. And that about the android users ?

No the only proper thing to do is a web server. As I dont thing they are going to change the internet for the next 10 years ! Not like the 6 month for phones.

 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #95 on: July 06, 2011, 09:02:54 am »
Talk about hijacking a thread! The OP asked for comments on HIS kickstarter handheld meter, now we are talking (bickering?) about a non existing bench meter project! Chill out Peebs :)
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

Offline joegtp

  • Contributor
  • Posts: 30
Re: Open Source Multimeter
« Reply #96 on: July 06, 2011, 12:17:06 pm »
This seems like a repeat of another thread a while back -- https://www.eevblog.com/forum/index.php?topic=173.0

Open source projects just don't start like this. It's going to take one maybe two people to be the leads and just do it. And by "do it" I mean do 90% of the initial work. You are never going to get anywhere by committee. If the decision is made to use LEDs instead of a graphical display are you still going to be motivated enough to work on the project? What about handheld vs benchtop? USB vs Wireless? Battery powered vs plugged in? There are way too many decision points and anyone of those will probably lessen your motivation to work on the project.

I love the idea of having an open source electronics bench: power supply, DMM, logic analyzer, etc. But this is not how it's going to happen.
 

Offline Zad

  • Super Contributor
  • ***
  • Posts: 1013
  • Country: gb
    • Digital Wizardry, Analogue Alchemy, Software Sorcery
Re: Open Source Multimeter
« Reply #97 on: July 07, 2011, 02:09:14 am »
Yes, the larger a group gets, the less likely it is to go anywhere. Linux was 1 man (plus GNU of course) and the ARM was just 2 people with no money and no resources. Similarly, the Mars rovers team had nothing for development and a very difficult deadline to hit. 

The important thing is to set realistic goals and get on with it. If you get diverted with 4 isolated channels, LCR/ESR and so on, then it will never get anywhere. Publish your results when you get a good design, and then if other people want to make their own machine then that is up to them.

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #98 on: July 07, 2011, 02:46:39 am »
I've said it before. I'm convinced the optimum number of people to work on a project like this and make the decisions rounds down to 1, almost always.

Dave.
 

Offline Mechatrommer

  • Super Contributor
  • ***
  • Posts: 10308
  • Country: my
  • reassessing directives...
Re: Open Source Multimeter
« Reply #99 on: July 07, 2011, 04:24:07 am »
well 3x, near 3K view in a week (and 7 pages) hit on "Open Source" topic! what do we have got here?
It's extremely difficult to start life.. one features of nature.. physical laws are mathematical theory of great beauty... You may wonder Why? our knowledge shows that nature is so constructed. We simply have to accept it. One could describe the situation by saying that... (Paul Dirac)
 

Offline firewalker

  • Super Contributor
  • ***
  • Posts: 2397
  • Country: gr
Re: Open Source Multimeter
« Reply #100 on: July 07, 2011, 02:13:47 pm »
I've said it before. I'm convinced the optimum number of people to work on a project like this and make the decisions rounds down to 1, almost always.

Dave.

And usually the outcome is better than a same project with many peoples taking decisions.

And as we say in Hellas "When to many rosters are singing, it delays the dawn" (it really looses its value in English).

"Opou laloun polloi kokoroi, argei na xhmerwsei"

Alexander.
« Last Edit: July 07, 2011, 02:17:46 pm by firewalker »
Become a realist, stay a dreamer.

 

Offline XynxNet

  • Regular Contributor
  • *
  • Posts: 185
  • Country: de
Re: Open Source Multimeter
« Reply #101 on: July 07, 2011, 03:18:48 pm »
Some sort of a generic sensor interface would be nice.
At the top of the meter you could plug in little addon sensor modules, which consists of a small mikrocontroller for callibration data and conversion tables and of course the sensor (light, sound, vibration, pressure, etc.). The meter suplies the power for the sensor module and displays and logs the sensor data.
 

Offline ruku

  • Contributor
  • Posts: 25
Re: Open Source Multimeter
« Reply #102 on: July 07, 2011, 07:50:44 pm »
I've said it before. I'm convinced the optimum number of people to work on a project like this and make the decisions rounds down to 1, almost always.

Dave.

Dave, that's the way to make decisions quickly! Not necessarily the best decision, perhaps... but certainly better than design by committee. However, I still wonder if Open Source Hardware can gain a little momentum from how Open Source Software works. Perhaps once these folks get it rolling, they can bring it in for community assistance.
 

Offline Frant

  • Regular Contributor
  • *
  • Posts: 54
Re: Open Source Multimeter
« Reply #103 on: July 07, 2011, 08:13:07 pm »
Some sort of a generic sensor interface would be nice.
At the top of the meter you could plug in little addon sensor modules, which consists of a small mikrocontroller for callibration data and conversion tables and of course the sensor (light, sound, vibration, pressure, etc.). The meter suplies the power for the sensor module and displays and logs the sensor data.

The family of standards IEEE 1451.x suggests several solutions. To be more specific, 1451.1 and 1451.2, or 1451.4 could be considered, the others are too complex and don't make sense in this case. However, adding more features has to stop at some point.
 

Offline Mechatrommer

  • Super Contributor
  • ***
  • Posts: 10308
  • Country: my
  • reassessing directives...
Re: Open Source Multimeter
« Reply #104 on: July 08, 2011, 02:59:41 am »
I've said it before. I'm convinced the optimum number of people to work on a project like this and make the decisions rounds down to 1, almost always.
Dave.
Dave, that's the way to make decisions quickly! Not necessarily the best decision, perhaps... but certainly better than design by committee. However, I still wonder if Open Source Hardware can gain a little momentum from how Open Source Software works. Perhaps once these folks get it rolling, they can bring it in for community assistance.
during most meeting i've attended, the more efficient way is someone (leader?) to prepare a complete program tentative for everybody to agree/discuss, rather than meet together and talk from nothing, which risk in the end of meeting you still have nothing. so, imho, in order for open source to work, someone has to prepare a working circuit/product to present and improvement or open source effort will start from there. and someone who started it has to be competent or "soundly" knowledgable so other dont have to improve trivial things/aspects.
« Last Edit: July 08, 2011, 03:01:58 am by Mechatrommer »
It's extremely difficult to start life.. one features of nature.. physical laws are mathematical theory of great beauty... You may wonder Why? our knowledge shows that nature is so constructed. We simply have to accept it. One could describe the situation by saying that... (Paul Dirac)
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #105 on: July 08, 2011, 03:18:21 am »
Dave, that's the way to make decisions quickly! Not necessarily the best decision, perhaps... but certainly better than design by committee.

Not if you get one really smart person who knows that they are doing.
Such a person is worth a hundreds grunts working a project.

Quote
However, I still wonder if Open Source Hardware can gain a little momentum from how Open Source Software works.

Likely not, they are two different beasts.
Ok, in theory it can, but in practice it never works that way.
Code is just code, you don't have to worry about manufacturing, physical usability, part availability, power consumption issues etc, and everything that goes along with that. It's a whole different ball-game.
For example, open source software like this BBS forum works because you can build a nice code base, and then everyone can pitch in and write plug-in modules to help expand it, building block style. The project gets bigger and better with time, but still remains the same beast underneath.
You can't really do the same thing with hardware. By it's very nature, hardware lends itself more toward complete physical change with each design iteration. It's not easy to reuse and build upon existing physical blocks in the same manner.
Sure you can reuse bit of schematics as building blocks, and some firmware, but that's about as far as it goes practically.

Dave.
 

Offline Harvs

  • Super Contributor
  • ***
  • Posts: 1200
  • Country: au
Re: Open Source Multimeter
« Reply #106 on: July 08, 2011, 05:04:52 am »
Thoroughly agree with Dave's comments about open-source hardware.  Lets be realistic, open hardware has been around since valves and electronic magazines, this is no new concept and it hasn't revolutionized hardware development yet.  The only people who really seem to be pushing this concept are the PCB "studios" selling the boards made from other peoples designs.

Maybe I'm just a cynic, however when I see phrases such as "Agile development for hardware", I tend to think they don't have a clue about how decent hardware is designed.
 

Offline zunklimt

  • Newbie
  • Posts: 3
Re: Open Source Multimeter
« Reply #107 on: July 08, 2011, 09:17:14 am »
wouldn't a modular approach be best the solution?

a solid base to begin with and then add new plug ins with new capacities

if that works for audio synthesis and arduinos, it should also work for professional measurement equipment.

using the smallest smd parts and good design, i'm sure it would be possible to do very small modules, maybe as small as lego pieces or with few squared centimetres

everyone could then arrange its metering system as desired: hand-held or bench, big or small, vertical or horizontal, simple or complex, wired or wireless, with as many channels as desired, with or without that or that capacity...

a well thought unified system for interconnection and physical attachment between the small modules would be the key to get a solid piece of gear at the end...

i know this wouldn't be the easiest to design (both ergonomically and electronically) but the result would then have the best for everyone...


but then, maybe simply doing a good arduino shield with the adequate circuitry to use it as a serious multimeter would also be a way...

if arduino itself is not good enough, maybe using the maple from leaflabs.com ...
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #108 on: July 08, 2011, 09:50:12 am »
wouldn't a modular approach be best the solution?

a solid base to begin with and then add new plug ins with new capacities

if that works for audio synthesis and arduinos, it should also work for professional measurement equipment.

It almost certainly won't.
The design will just end up big, expensive, and clunky, and likely not satisfying anyone requirement.
It been tried before many times over the decades, and it just never ends up working, there are just too many design intricacies involved with most projects.

You could possibly have some module thing with a multimeter like this, in fact I was thinking separate modular boards for the inputs. But it's not like you can them go do the same thing with say displays etc.

Quote
but then, maybe simply doing a good arduino shield with the adequate circuitry to use it as a serious multimeter would also be a way...
if arduino itself is not good enough, maybe using the maple from leaflabs.com ...

Arduino or any system like that is not the right solution for something like this. It has to be fully custom.

Dave.
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #109 on: July 08, 2011, 10:02:16 am »
Thoroughly agree with Dave's comments about open-source hardware.  Lets be realistic, open hardware has been around since valves and electronic magazines, this is no new concept and it hasn't revolutionized hardware development yet.  The only people who really seem to be pushing this concept are the PCB "studios" selling the boards made from other peoples designs.

Yes, nothing new at all. Every magazine project ever published for the last 50+ years is open hardware, it just didn't have that name.
Some projects even got "built on" by other people.
My DSOA project for example, Jim Rowe at EA magazine took that design and produced the Mk2 unit. Used the same PC interface and core circuitry for software compatibility, but got a whole new PCB, new case, and new controls, turning it into a better unit (albeit, much more expensive).
Ok, so doesn't that prove that open hardware works like software?
Well, yeah, for that one iteration only.
If you wanted to go beyond that (which I did with the Mk3), it quickly becomes clear you have to scrap that design entirely and start again from stratch. There is only so far you can build upon a hardware project before it become non-optimal and a better new approach is required. That usually means an almost complete re-design.

Dave.
 

Offline jahonen

  • Super Contributor
  • ***
  • Posts: 1046
  • Country: fi
Re: Open Source Multimeter
« Reply #110 on: July 08, 2011, 12:56:32 pm »
Btw, in case nobody remembers, we seem to had this kind of discussion in the past, see Community Bench Meter. It didn't seem to lead to anything, as nobody did not really want to spend some time on it. Fancy things are usually 99% hard boring work, 1% of the fun stuff.

Regards,
Janne
 

Offline Chasm

  • Regular Contributor
  • *
  • Posts: 211
Re: Open Source Multimeter
« Reply #111 on: July 08, 2011, 04:43:21 pm »
99% of the fun stuff is usually doing the design, once you move beyond it the work starts and the fun is over. That the the moment where most remember that they don't need the device anyway and that "Because I can!" alone is not sufficient motivation. ;)
 

Uncle Vernon

  • Guest
Re: Open Source Multimeter
« Reply #112 on: July 09, 2011, 01:46:10 am »
I'm just a little curious on peoples perceptions of open source an on the comparisons between OSH and OSS.

Open source doesn't dictate design by committee it's more about freedom and transferal of effort and expertise an alternative to "get what your given" and "don't reverse engineer or we'll sue" corporate models.

The comparisons between a proposed multimeter project and open source Linux don't make a lot of sense. If you think for a section about what a Linux distribution is, you can see it is a collection of tools. And just like our multimeter should be, many of those software tools are solo or small team efforts.

To build the ultimate multimeter is like trying to build the best car or the ideal home, there is no such thing and there never will be.  You can only achieve your ultimate, a committee driven thing will always be a collection of compromises. Look at the software comparison the Linux world is full of many similar tools with differing feature sets, open source gives the freedom to select your own best fit collection of tools.

If we were to achieve the hardware equivalent of Linux, we'd be bringing together lots of different open source hardware items and sharing the knowledge. Cant find a power supply that perfectly fits your needs? Then borrow the best bits of existing designs and build your own and share the knowledge you gain along the way. Same for meters or any other piece of equipment.

Open source has found favour from those who felt penned in by commercial offerings. Microsoft anyone? The need exists for any operating system that doesn't demand it's users to the company line. I'm not so sure the same need exist with a multimeter, Fluke aren't trying to tell me how to do my work, Microsoft is, and that's why I utilise Microsoft alternatives wherever I can.

Where open source hardware would really thrive is in areas like domotics, where anyone could select the collection of products and designs that suits their particular want, need and cave size to achieve their unique personal build.

I'm enthusiastic about open source and see it as a worthwhile pursuit, and while I see this open source meter as a bit like pushing string uphill, I'd still love to be proven wrong. Seeing what doesn't work and understanding why can still be some of the most useful engineering there is.

Feel free to discuss, dismiss, agree or deride to your heart's desire.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #113 on: July 09, 2011, 09:41:52 am »
I agree with Dave that you can't compare open source software with hardware.

One fundamental difference is with hardware, there's the physical cost of components and manufacture which doesn't exist with software. A software producer doesn't have to worry about cost per unit whether their open source or not. All a commercial software developer needs to do is ensure the revenue they make from sales covers the cost of development, plus a bit of profit.

The physical cost of a single unit of an additional software licence is always near zero. A hardware developer needs to get their product made and sold. The physical cost per unit will always be the price of the components, plus manufacturing and shipping. This is why software piracy is not really stealing. A software vendor doesn't directly loose the value of 1000 licences because someone uploads their software to a file sharing site. A hardware developer would loose the value of 1000 DVMs if someone hijacked a lorry carrying their meters.

A software developer is always foolish, if they're unwilling to negotiate on price. An extreme is example: Altium would be better off selling me a copy of their latest design package for £100 than me either not buying it or pirating it. If they don't sell the software to me the get nothing, if they do sell it to me for £100, they get £100 and their only cost is shipping a DVD to me, £10 at the most in administrative costs,, shipping etc.

In my opinion, the best open source project would be something like an oscilloscope developed by a commercial seller who made the source code for all of the firmware public and encouraged people to improve it, fix bugs and write translations.
 

Offline Bored@Work

  • Super Contributor
  • ***
  • Posts: 3933
  • Country: 00
Re: Open Source Multimeter
« Reply #114 on: July 09, 2011, 10:19:40 am »
This is why software piracy is not really stealing.

Bullshit. You are just doing the usual word games. Word games software thief do to cover up that what they do is wrong. It doesn't matter how you call it, and how many arguments you pull out of thin air. It is wrong.

Quote
In my opinion, the best open source project would be something like an oscilloscope developed by a commercial seller who made the source code for all of the firmware public and encouraged people to improve it, fix bugs and write translations.

Oh, you mean the Wittig/Wellec oscilloscope? Three years or so of community "enhancements" of the software and still doesn't beat a cheaper Hantek or Owon.
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #115 on: July 09, 2011, 11:32:03 am »
This is why software piracy is not really stealing.

Bullshit. You are just doing the usual word games. Word games software thief do to cover up that what they do is wrong. It doesn't matter how you call it, and how many arguments you pull out of thin air.

Wow, what an informative post!

Thanks for wiring a detailed and well reasoned argument as to why it is stealing.

Quote
It is wrong.
I didn't say that software piracy is not wrong. I just said it isn't stealing. You can't call it stealing because the unit value of a piece of software is effectively zero. Copyright infringement, voiding of a contract yes but physically stealing isn't the right word for it.

Of course if everyone pirated software no one would make any money from it but they do and software companies have actually encouraged piracy in the past and still do today, especially in emerging markets to increase the user base.

Anyway, I'll stop now. I don't want to turn this thread into flame war on piracy. I just wanted to point out it isn't as simple as many say.

Quote
Oh, you mean the Wittig/Wellec oscilloscope? Three years or so of community "enhancements" of the software and still doesn't beat a cheaper Hantek or Owon.
I admit I have no experiences of such oscilloscopes so can't comment. Have you?
 

Offline Mechatrommer

  • Super Contributor
  • ***
  • Posts: 10308
  • Country: my
  • reassessing directives...
Re: Open Source Multimeter
« Reply #116 on: July 09, 2011, 03:48:08 pm »
why dont we just limit the OSH definition to schematic level, not up to pcb/product manufacturing. with only schematics to improve, we can later make our own way on how to manufacture it. and with OSH, you should not expect profit as much as the CSH (closed source) can. something like 50% will buy, 50% will diy or pirate, the figure could be wrong, i just want to demo the idea.
It's extremely difficult to start life.. one features of nature.. physical laws are mathematical theory of great beauty... You may wonder Why? our knowledge shows that nature is so constructed. We simply have to accept it. One could describe the situation by saying that... (Paul Dirac)
 

Offline joegtp

  • Contributor
  • Posts: 30
Re: Open Source Multimeter
« Reply #117 on: July 09, 2011, 04:44:49 pm »
I still don't think group OSH will work.  Simple scenario, I'm a project creator/lead and I want to build a single channel, no graphic LCD, really precise, handheld DMM. If you don't share that same exact goal, hardware design fall apart. If you as a contributor, add channels it will increase not only your cost but mine. If you add a graphics LCD again it would completely change the design possibly requiring a new uC more PCB space, etc.. You get the idea. 

In OSS if you add a wizbang GUI it doesn't really effect me. As the project leader the cost and change to what I use and want it for does not change. Although sometimes it does and that's why you see 20 flavors of linux distros.

Software, at least good software, is very modular and parts can be swapped in and out without a whole lot of problem. That's why I think Arduino is so popular, shields can be added and removed, IO pins are exposed to be expanded upon. Which for a hobby, just playing around scenarios, that works great. But once you try and build a product or do something fancy it starts to fall apart.

Look at Arducopter (http://code.google.com/p/arducopter/),They started off using a standard arduino mega board but the requirements required a custom board which is where they are today. I also believe it started as one guy designing the whole hardware. But now that the hardware is mature all sorts of people are contributing software. Sure the board is OSH but in the end one guy design and built it to the point that it fully worked before others started stepping in.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #118 on: July 09, 2011, 06:07:28 pm »
why dont we just limit the OSH definition to schematic level, not up to pcb/product manufacturing. with only schematics to improve, we can later make our own way on how to manufacture it. and with OSH, you should not expect profit as much as the CSH (closed source) can.
Schematics aren't very helpful for modern oscilloscopes, at least half of the design is in the firmware.

Quote
something like 50% will buy, 50% will diy or pirate, the figure could be wrong, i just want to demo the idea.
What do you mean? Being open source means you give permission to redistribute so piracy would mean someone violating the GPL such as making modifications and selling the design without releasing the source code.

If you're talking about piracy of proprietary software it probably varies widely. Software with a larger user-base will obviously be pirated more and more expensive software is probably likely to have a higher piracy vs legitimate user ratio. Other factors such as the type of demographic of the user-base and DRM also make a difference. The answer is no one  really knows.
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #119 on: July 10, 2011, 07:03:39 pm »
Hello there, first post on the forum...

I've been pondering with the idea of data acquisition for over a year. You know, cobbling together some sensors, do the signal munching and data crunching and pass the data to a PC to be displayed and recorded.So I was thinking whether or not it would be a good idea if I brought the subject to Dave, whom I don't know except watching his videos on YouTube. Since I don't know how to design electronics it occurred to me that it may not be such a good idea to push half baked ideas to people I don't know in order to get them to design it for me.

Anyway PXI was mentioned in the thread and since I was drooling over it for long time I decided to go ahead and draw things as I imagined them. So I put together most of the ideas I liked from the forum to see what it would look like.

Design criteria as follows:

- Should use PXI form factor.

I really like PXI. It has everything necessary for measurement and control work. Basically it is a PCI bus with a few additions like precision timing, star triggering etc.

The physical layer of PXI is taken from IEEE 1101.10 which is the standard dealing with Eurocard physical dimensions which are ment to go in 19" racks. Since this is worldwide standard finding cases and hardware should be easy and cheap.

http://ph-dep-ese.web.cern.ch/ph-dep-ese/crates/standards/1101_1.pdf

The backplane of PXI is largely based (but not exactly the same) on CompactPCI which is also industry standart.

Other than that everything revelant is published on
http://www.pxisa.org/Specifications.html

All in all a community designed multimeter has best chances of survival if it is based largely on industry standard  hardware. Thus it can live inside many standard cases side by side with commercial stuff and other community gadgets like LCR's, Load cell amplifiers, Thermocouple modules, Frequency generatos, counters, relay boards, SDR's etc. etc.


- Standart Commercially available case

As I said, I am all for PXI and if this multimeter is ever developed I'd stick it in a 3U Rack with all the other community developed things to go with it. However the conversation is about a hand held device so i drew it as such. My point is that you can have both PXI and "Hand Held" at the same time. This case can house two PXI units. If it ever becomes available, users can switch one of the channels for a LCR for example.

   The box on the pictures is BOPLA Aluplan 51020 it measures 245mm Lenght x 143mm Width x 52mm Height. It is made from aluminium extursions. Top and bottom covers are 3mm thick everything else is thicker. Corner pieces are zinc castings. I don't know how much it costs but sure beats 30.000$ tooling cost for custom case.
    http://www.bopla.de/en/product-catalog/enclosure-technology/product-category/aluplan-13/product-detail/ap-51020-2.html

It is ment to be held sideways so that when sitting inclined on a bench the probe cables are sticking out from the right side - away from where your hands would be when pushing the buttons.

- Enough space for batteries

   Currently it has 4 AA cells inside. Maybe it can accomodate 4 D cells if very slightly bigger box was chosen. I think a power input should be made available as well. So that the gadget can work for months measuring away some mundane thing an give alarm and start logging data only if some alarm condition is met.

Something like "Give alarm and log data as long as Channel #1 voltage is below 6.25V AND Channel #3 Temp is above 99 Degrees Celsius" Which would mean that your chemical reaction is underway even when you are not applying power. Which may as well mean that you hit the Jackpot and you are going to be rich.

- Good User Interface

Dave said he likes 7 segment dispalys but 4 dispalys with 5 digits each? I'd prefer a good ole monochrome LCD please. The one on the picture is 100mm x 70 mm (say 4 by 3 inches). Button arrangement is inspired from aircraft interfaces with a screen and soft buttons around it. A slight twist is the two row buttons on the right side which may be used to alter preferences without entering menus.
   





Front View



Side View




Side View - Connection Jacks



Cross Section - To show what goes where


The small PCB behind the batteries is the "PXI Back-plane" of course it is not standard.it connects only 3 modules (the main board with the display is also a module)






This is standard Eurocard size 3U. PXI, CompactPCI, IEEE 1101.10 and probably many others all use this form factor. Sockets at the back side change from standard to standard.



Well, I'd like to hear what you think

Edit: Dave mentioned these sketches on The Amp Hour.
        Starts around 0:20:05
« Last Edit: July 13, 2011, 09:35:18 am by HLA-27b »
 

Offline Frant

  • Regular Contributor
  • *
  • Posts: 54
Re: Open Source Multimeter
« Reply #120 on: July 10, 2011, 08:24:49 pm »
Well, I'd like to hear what you think

Impressive work!
 

Offline Joshua

  • Regular Contributor
  • *
  • Posts: 194
  • Country: us
Re: Open Source Multimeter
« Reply #121 on: July 11, 2011, 01:19:36 am »
Awesome Job! What CAD software is that?
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #122 on: July 11, 2011, 01:33:10 am »
Awesome Job! What CAD software is that?

Google SketchUp
it is free and by far the easiest one to use.
http://sketchup.google.com/

Edit: I attach the 3D files used to make the stuff above.
Please note that the non free version of SketcUp was used to create them.
« Last Edit: July 11, 2011, 02:23:54 pm by HLA-27b »
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #123 on: July 11, 2011, 12:29:49 pm »
Hello there, first post on the forum...

You win the first post of the year award!
Awesome.

Would it fit 2 x D cells?
That would still kill the capacity of 4 x AA's

Dave.
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #124 on: July 11, 2011, 01:40:22 pm »
It could fit 4 D cells if the case was some 10 - 15mm longer. So definitely possible with another case. In fact i pick this one a bit arbitrarily - it was the first one that could take 2 PXI boards so I used it straight away. 

I probably should post the 3D files so everybody can have a go at it. (Done look above)

On the other hand I would appreciate if you Dave (and all of you guys of couse) can elaborate on some questions I have in mind.

How much stuff could fit on 100mm x 160mm Eurocard?
2 separate channels with amps and everything or maybe just one volts channel and one amps channel?

What do you think of the PXI thing?
Do you think that once a community designed multimeter and a backplane is made available to the amateurs it would spur development of many other devices to go with it? LCR's Freq Generators etc?

Would you buy one if it was sold as a kit of pieces ?

For example a kit of
1 - PXI multimeter board (assembled and tested)
1 - Main board with processing LCD screen and buttons (assembled and tested)
1 - 1 backplane (to be assembled by the buyer)
1 - Box to be drilled and assembled by the buyer (takes two pxi units)

Any prognosis on the prices?
« Last Edit: July 13, 2011, 09:37:52 am by HLA-27b »
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 2488
  • Country: us
Re: Open Source Multimeter
« Reply #125 on: July 11, 2011, 02:48:11 pm »
What do you think of the PXI thing?
Do you think that once a community designed multimeter and a backplane is made available to the amateurs it would spur development of many other devices to go with it? LCR's Freq Generators etc?

I am not sure.  On the one hand, PXI is indeed really nice, and could be useful for more advanced test gear.  However, it isn't exactly very hacker friendly.  Even many advanced hobbyists are not likely to have the equipment to develop and test PCI devices.  It also seems like a low speed device like a DMM doesn't gain a lot here.  I would prefer a low speed serial bus (SPI or CAN) for communication between the modules, and then USB and ethernet on the controller /display module for interface to the outside world.  You loose the ability to directly plug into a PXI chassis and integrate with other PXI test gear, but that stuff is usually pretty expensive and out of reach of most hobbyists.
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #126 on: July 11, 2011, 04:17:16 pm »
...However, it isn't exactly very hacker friendly... 

On the contrary, PXI lets you leave out features that you don't use. As a bare minimum you have to implement J1 socket.
J1  is for power, 33MHz clock and 32 bit data, 10MHz precision clock and triggering.

You can omit any of these unless you need 'em.
If you don't need precision clock and triggering you simply don't connect to the pins.
Likewise if you don't need 32 bit data you can limit yourself to 8,16,24 bits.
Other boards connected to the same back-plane are not affected.
(you probably knew all these but I didn't until yesterday) 

This only leaves out the backplane, which happens to be passive,
 and the processing board which I imagine as something akin to Beagle board

So while not exactly piece of cake it is not hacker unfriendly either.



 

Offline Mechatrommer

  • Super Contributor
  • ***
  • Posts: 10308
  • Country: my
  • reassessing directives...
Re: Open Source Multimeter
« Reply #127 on: July 11, 2011, 06:24:33 pm »
that thing looks like oscilloscope.
It's extremely difficult to start life.. one features of nature.. physical laws are mathematical theory of great beauty... You may wonder Why? our knowledge shows that nature is so constructed. We simply have to accept it. One could describe the situation by saying that... (Paul Dirac)
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 2488
  • Country: us
Re: Open Source Multimeter
« Reply #128 on: July 11, 2011, 06:40:50 pm »
...However, it isn't exactly very hacker friendly... 

On the contrary, PXI lets you leave out features that you don't use. As a bare minimum you have to implement J1 socket.
J1  is for power, 33MHz clock and 32 bit data, 10MHz precision clock and triggering.

You can omit any of these unless you need 'em.

Interesting.  I haven't looked much at PXI from the hardware side, and it has been a few years since I had to deal with PCI.  The precision timebase and trigger bus aren't what worry me, it is the PCI.  I am under the impression that you still have to implement a complete PCI interface -- arbitration, enumeration, and so forth.  That means an FPGA, a dedicated bridge chip, or a processor with PCI built in.  None of those is out of the realm of a hobbyist to implement, but it can be tricky to debug without a logic analyzer.
 

Offline Bloch

  • Supporter
  • ****
  • Posts: 444
  • Country: dk
Re: Open Source Multimeter
« Reply #129 on: July 11, 2011, 06:51:29 pm »
Hello there, first post on the forum...

You win the first post of the year award!
Awesome.

So true.

But the PIX thing is not for me. I think there are a lot of work in that. But if I can buy one finished then no problem.

And it seems for me to be an "old" standard. Data in parallel is not the "new" way to do it. Think on IDE / SATA or Parallel port / USB.

At work i uses a lot of time on PLC's. And there is the "new" standard EtherCat. Buzzwords free and open / fast / True Time stamps / and just works on  Ethernet.

But if i get a vote  :) then i think on a RS232/USB >  KISS = keep it simple and straightforward
 

Offline JimHorn

  • Contributor
  • Posts: 6
  • Country: us
Re: Open Source Multimeter
« Reply #130 on: July 13, 2011, 06:15:17 am »
One DMM feature I've always wanted has been standard on oscilloscopes for decades: 1, 2, 5 range switching.  With modern digital calibration and LSI, it should be simple to provide.  And it would mean that a small increase in a measured value wouldn't suddenly cost you 90% of the instruments resolution.

Yes, it means many measurements would have only even or just 0 or 5 as the last digit but the microprocessor running the show could easily show the error band or resolution if asked (another button function?).  Most manuals include the instrument accuracy and resolution specs but who remembers those in use?  The instrument should...
So many signals, so little bandwidth!
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 2488
  • Country: us
Re: Open Source Multimeter
« Reply #131 on: July 13, 2011, 07:27:34 am »
I would always rather just have more counts.  Unnecessary range switches are too annoying, and the resolution and dynamic range of the modern sigma-delta converters is such that the number of displayed counts is set by the display size and the component accuracy, not the ADC.
 

Offline hisense999

  • Contributor
  • Posts: 39
Re: Open Source Multimeter
« Reply #132 on: July 14, 2011, 04:06:29 am »
A software developer is always foolish, if they're unwilling to negotiate on price. An extreme is example: Altium would be better off selling me a copy of their latest design package for £100 than me either not buying it or pirating it. If they don't sell the software to me the get nothing, if they do sell it to me for £100, they get £100 and their only cost is shipping a DVD to me, £10 at the most in administrative costs,, shipping etc.

It's a wrong point of view, Altium is not a fresh computer game which selling in milions of copies monthly but dedicated software - trust me even if this cost £10 ppl still will preffer to use pirate copies. Dedicated software must be expensive and base on selling it into companies, Altium don't care about you and your £100 Altium care about big companies selling them hundreds of seats Altium also don't care if you pirate it even this is good cuz then is possibility to make you stick with Altium software and one day maybe you open a company and must to buy original one, or in further work you push your boss to get Altium for PCB design.

Anyway as I also selling software I know is better to sell 1000 copies than 10000 is same profit but more small amount of customers to handle.

Just last time my company maked an experiment and we selling software really cheap, belive me we never make this mistake again amount of customers to handle was groving up day by day but amount of income money was a nothing compared to previous products, was more headache than profit on this. And at final you can discover you reach a peak point where sales only will go down cuz you cover with your dedicated software ~40% of possible end customers and then profit is decrasing month by month and wishes of existing customers are incrase whole team start to be tired of tips going from sales and huge amount of work needed to make first existing customers happy and then improvements to catch new customers.

And remember dedicated software is not an game you cannot leave it with bugs and without updates or design a "Your Software 2" cuz dedicated group of customers have already this which make them happy and for prepare improvements and something which can be push as new product for which you can charge a new money is not only to redesign levels in game and a little improve graphics but built dozens of complicated things from beginning.

P.S.
Sorry for my poor english :)

B.R.
 

Offline hisense999

  • Contributor
  • Posts: 39
Re: Open Source Multimeter
« Reply #133 on: July 15, 2011, 03:53:41 pm »
About whole project, is it not better with Open Source Multimeter to just make a real fun hack - just to take a most cheap multimeters which are flooding a market and sometimes cost 2$ and redesign HW inside (maybe even to add own MCU) giving for it super accurate results and new features... I know only 4 digits and no special connectors but if this must be a real open hardware multimeter then this must be something which other ppl are able to make in home without ordering special housing, 2pcs of LCD, custom PCB (the best soldered already cuz then for sure will match specs), so why is not better to pick up most cheap multimeters on the market and check which can be most easy to hack. I speak about perfect hack - additional small board with own MCU inside and only modify existing PCB for replace some crappy components with quaility ones adding some wires and then is a big chance for make open source multimeter for ~20USD which anyone can rebuild in home.

B.R.
 

Offline FreeThinker

  • Frequent Contributor
  • **
  • Posts: 791
  • Country: england
  • Truth through Thought
Re: Open Source Multimeter
« Reply #134 on: July 15, 2011, 06:34:54 pm »
About whole project, is it not better with Open Source Multimeter to just make a real fun hack - just to take a most cheap multimeters which are flooding a market and sometimes cost 2$ and redesign HW inside (maybe even to add own MCU) giving for it super accurate results and new features... I know only 4 digits and no special connectors but if this must be a real open hardware multimeter then this must be something which other ppl are able to make in home without ordering special housing, 2pcs of LCD, custom PCB (the best soldered already cuz then for sure will match specs), so why is not better to pick up most cheap multimeters on the market and check which can be most easy to hack. I speak about perfect hack - additional small board with own MCU inside and only modify existing PCB for replace some crappy components with quaility ones adding some wires and then is a big chance for make open source multimeter for ~20USD which anyone can rebuild in home.

B.R.
Problem is that there is very little inside to hack & the build quality is crap! Non starter sorry :-\
Machines were mice and Men were lions once upon a time, but now that it's the opposite it's twice upon a time.
MOONDOG
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #135 on: July 15, 2011, 07:10:07 pm »
I think we should start to spec out this thing already.

So here I ask the question:

What should the analog section look like? What should be the specs?
 

Offline rfdave#gmail.com

  • Contributor
  • Posts: 22
  • Country: us
Re: Open Source Multimeter
« Reply #136 on: July 16, 2011, 02:49:30 am »
How about starting out with a simple USB/1 channel dmm box. Once that's done and working, it's a fairly simple module to plug into other systems.

Dave
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #137 on: July 16, 2011, 01:35:53 pm »
It's a wrong point of view, Altium is not a fresh computer game which selling in milions of copies monthly but dedicated software - trust me even if this cost £10 ppl still will preffer to use pirate copies. Dedicated software must be expensive and base on selling it into companies,
Yes, may be I took it to the extreme but you know what I mean.

Quote
Altium don't care about you and your £100 Altium care about big companies selling them hundreds of seats Altium also don't care if you pirate it even this is good cuz then is possibility to make you stick with Altium software and one day maybe you open a company and must to buy original one, or in further work you push your boss to get Altium for PCB design.
You're certainly right there - I've said that before.

Quote
Anyway as I also selling software I know is better to sell 1000 copies than 10000 is same profit but more small amount of customers to handle.

Just last time my company maked an experiment and we selling software really cheap, belive me we never make this mistake again amount of customers to handle was groving up day by day but amount of income money was a nothing compared to previous products, was more headache than profit on this. And at final you can discover you reach a peak point where sales only will go down cuz you cover with your dedicated software ~40% of possible end customers and then profit is decrasing month by month and wishes of existing customers are incrase whole team start to be tired of tips going from sales and huge amount of work needed to make first existing customers happy and then improvements to catch new customers.
Interesting, so you don't want too many customers because it increases support costs.

So why not just reduce the price of the licence and charge more for support?

Surely that sounds like the best business model? Sell relatively inexpensive licences to hobbyists with terms such as not for commercial use and no support and make the real money from big  companies.

Offering small companies special deals would also be a good idea.

Quote
And remember dedicated software is not an game you cannot leave it with bugs and without updates or design a "Your Software 2" cuz dedicated group of customers have already this which make them happy and for prepare improvements and something which can be push as new product for which you can charge a new money is not only to redesign levels in game and a little improve graphics but built dozens of complicated things from beginning.
I don't know if I agree with that, I use AutoCAD electrical at work and it's as buggy as Windows 95 was at its initial release and crashes just as often.
« Last Edit: July 16, 2011, 05:23:23 pm by Hero999 »
 

Offline Joshua

  • Regular Contributor
  • *
  • Posts: 194
  • Country: us
Open Source Multimeter
« Reply #138 on: July 16, 2011, 02:08:21 pm »


So why not just reduce the price of the licence and charge more for support?

Surely that sounds like the best business model? Sell relatively inexpensive licences to hobbyists with terms such as not for commercial use and no support and make the real money from big  companies.


I don't know if there's anything I despise more than when a company won't answer a simple phone call question unless you pay for that support. I.e. Microsoft, apple, HP...
 

Offline hisense999

  • Contributor
  • Posts: 39
Re: Open Source Multimeter
« Reply #139 on: July 16, 2011, 02:47:19 pm »
So why not just reduce the price of the licence and charge more for support?

Surely that sounds like the best business model? Sell relatively inexpensive licences to hobbyists with terms such as not for commercial use and no support and make the real money from big  companies.

Offering small companies special deals would also be a good idea.


Is more easy to decrase than incrase prices especially when all is based on distributors network which bought stock already and software is not license based but fisical security dongle based, everything always have more deep story inside even when looks very simple.

And with Altium and non-commercial use this is very good idea especially when this also include limitation to two layers boards then this can be perfect deal for hobbysts and good protection for Altium.

B.R.

P.S.
About OpenSource multimeter the most important is to choose enclosure\housing also exist another OpenSource possibility - 3D project which everyone with MakerBot, RepRap or UP! 3D plastic printer can be able to print, just now many ppl have 3D printers and price of it is decrased every year, so community with 3D printers can be supplier for it :)
« Last Edit: July 16, 2011, 02:54:11 pm by hisense999 »
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #140 on: July 16, 2011, 08:47:50 pm »
Here's my own take on the subject. Feel free to pick it to pieces.

As this thread demonstrates, everybody's going to have their own requirements for an ideal multimeter. As such, the thing should be made modular so the end user can swap out parts to fit their needs, rather than trying to create a one size fits all meter as everybody and their brother has done.
In that case, the base meter would be a rack-like case with some basic infrastructure that all designs would need: Physical structure for the meter, battery holder(s), a processor, slots for modules (consisting of mechanical supports and a standard set of electrical connections) and such. The modules would be in two or three from factors. A small, simple input module that could handle basic functions like voltage, current, resistance, etc. These modules would ideally interlock horizontally so 3 or 4 of them could be lined up rack style (no dead space between modules) at the bottom of the meter, resulting in the multi-input design dave is after. Measurement circuitry requiring more space could be built in double or triple-wide modules.
Display modules would cover the full width of the meter and as I said above and possibly be designed around a bus so they could be stacked as necessary.
Controls could be integrated into these display modules, exist as a dedicated display module, or perhaps a third control panel type module is in order.
Point being, people can easily assemble a meter to meet their own needs and leave out the extra stuff.
This would turn the open-meter into a set of standards… The mechanical specs of the modules, communications between each module and the processor, current demands and such. Once you've got that, anyone can create their own modules to expand the meter's abilities. To facilitate that, blank modules (just the plastic housing and maybe standard connectors) could be sold, as well as populated V/I/R/C, LCD and control modules.
Since the modules and services would be standardized, alternative form factors for the meter "rack" could be created as well. Rather than the standard meter housing with lots of module slots, a compact probe-style meter could be made with one or two input slots and a display slot. In that case, the input could be either banana jacks, a point probe with common jack, or tweezers like those obnoxiously expensive LCR meters. A bench-top model would also be perfectly reasonable… Power supply module maybe? That would allow disposable batteries, rechargeable or plug-in sources.


The battery is going to be user replaceable.
Is that particular battery a standard battery that will be in production x number of years from now?
Use something that is ubiquitous like the 18650 Li-ion cells. They're cylindrical, have AA-like proportions (though with larger dimensions) and typically provide around 2300 mAh @ 3.6V. In that case, AA-style battery holder designs (snap in, cradle with cover, caped tube, whatever) would be easy to adapt and would eliminate the need for device-specific battery packs. While they don't quite make the run-out-to-a-drugstore cut, they're used as the base cell in a lot of consumer devices. My older Acer netbook uses them. Judging from the shape, dimensions and specs of the battery pack, my dust buster uses them, and my cordless drill probably does as well. Point being that even if they become hard to find new, it should still be fairly easy to scrounge them out of old battery packs. Using individual removable cells means one can carry around a few extra if spending a lot of time in the field.
« Last Edit: July 16, 2011, 08:56:16 pm by bobski »
 

Offline rfdave#gmail.com

  • Contributor
  • Posts: 22
  • Country: us
Re: Open Source Multimeter
« Reply #141 on: July 16, 2011, 10:15:20 pm »
A proposed Starting spec

  • usb interface
  • powered from USB
  • 4 1/2 digit resolution
  • volts/amps/ohms scales
  • autoscaling
  • no buttons/controls on case, just banana plugs as input
  • 3 plugs-Common, Volts and Amps
  • Continuity test, fast response time
  • bench focused, so input voltage levels limited to 50v

This could serve as a module in some of the fancier setups, but without this basic functionality, you've got nothing.
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #142 on: July 16, 2011, 11:41:36 pm »
Here's my own take on the subject. Feel free to pick it to pieces.
....
In that case, the base meter would be a rack-like case with some basic infrastructure that all designs would need:

I agree and I don't agree. Racks are my preferred form factor as well. I wrote about PXI previously and maybe it can be made open source. Not the PXI itsel of course but a board designed to PXI may as well be open source.

What I don't agree is that maybe we are trying to tie this thing to a particular shape too early. It is not that voltmeters need racks (but racks need voltmeters...and other things).

This would turn the open-meter into a set of standards…


 IEEE - 1101.1 is one standard you would like to stick to. It governs the mechanical aspects of rack equipment. On the other hand what governs backplanes is not standards but industry specifications like PCI PCIe CompactPCI PXI etc. PXI is not a standard yet. At the moment it is a specification maintained by a consortium of companies. It may become standard in the future. Standards and specifications are quite an entangled mess. Maybe we should keep them beside the point for the time being. For all I know The Open Source Multimeter consists of a few guys trying to decide what ADC to use.
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #143 on: July 17, 2011, 12:38:42 am »
A proposed Starting spec

  • usb interface       Check
  • powered from USB        Likely an option
  • 4 1/2 digit resolution        Make that 6          https://www.eevblog.com/forum/index.php?topic=4087.msg55214;topicseen#msg55214
  • volts/amps/ohms scales   Check plus maybe Sourcing and LCR
  • autoscaling     Check
  • no buttons/controls on case, just banana plugs as input
  • 3 plugs-Common, Volts and Amps  4 plugs would enable Kelvin 4 wire measurements
  • Continuity test, fast response time   Check
  • bench focused, so input voltage levels limited to 50v     That seems dangerous
[/li]
[/list]

This could serve as a module in some of the fancier setups, but without this basic functionality, you've got nothing. Check
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #144 on: July 17, 2011, 01:47:30 am »
IEEE - 1101.1 is one standard you would like to stick to. It governs the mechanical aspects of rack equipment.
I see your confusion. I'm saying the meter would be like a rack in the sense that a rack provides multiple slots that can be occupied by a variety of equipment. I suppose what I'm thinking of has more in common with PLCs. For those not familiar with them, PLCs are computers used for industrial automation. The hardware consists of a rack with built in power supply and a series of slots for cards. The slots are all interconnected by a backplane board. The first card is a CPU card with processor, memory and basic run/stop controls. The remaining slots can be used for whatever is needed - input cards (analog or digital), output cards (relay-based digital, or analog), or hybrids of the two. If an assembly line gets re-tooled and different I/O connections are needed, you pop out one card, plug something else in it's place, update the software to reflect the change and away you go.
The form factor I'm thinking of is handheld multimeter-sized, though there's no reason you couldn't make a bigger or smaller "rack" that makes use of the same plug-in modules.
 

alm

  • Guest
Re: Open Source Multimeter
« Reply #145 on: July 17, 2011, 02:03:11 am »
USB power would require at least one isolated DC-DC converter, more if you want multiple channels. Probably not worth the complexity IMO.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #146 on: July 17, 2011, 07:28:40 pm »
USB power would require at least one isolated DC-DC converter, more if you want multiple channels. Probably not worth the complexity IMO.
Good point.

If you design the power supply it would need UL approval and buying one with a with a high enough isolation voltage for mains won't be cheap.

I was going to suggest the one in RS linked below but it's only rated for 3kV which won't be good enough for mains, although it'll be fine for SELV i.e. automotive or telecoms use.

http://uk.rs-online.com/web/p/dc-dc-converters/4943838/
http://docs-europe.electrocomponents.com/webdocs/0518/0900766b80518157.pdf
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #147 on: July 18, 2011, 02:15:50 am »
USB power would require at least one isolated DC-DC converter, more if you want multiple channels. Probably not worth the complexity IMO.

Here is some reading material about isolation and why it is required.

http://zone.ni.com/devzone/cda/tut/p/id/3410

For people like me who didn't know.
 

Offline Fox

  • Regular Contributor
  • *
  • Posts: 54
  • Country: de
  • Electronics Engineer
Re: Open Source Multimeter
« Reply #148 on: July 18, 2011, 10:33:48 pm »
A proposed Starting spec


This could serve as a module in some of the fancier setups, but without this basic functionality, you've got nothing. Check

Going from 4 1/2 Digits to 5 or even 6 Digits  will increase the complexity dramatic.
The ADC alone won't guarantee  the 6Digit resolution, one will need a very good analog signal conditioning circurtry.
e.g the Agilent U1242 has an 24bit ADC (ADS1242) like the LTC2415 but gives one "only" 10000 counts with its relatively "simple" input section, but the Fluke 28II with an 20Bit ADC (LTC2435) gives one 20000 counts with a better input section.
So keeping 4 1/2Digits resolution would increase the possibility of success of an open source Multimeter
A closed Switch should have zero Ohms or less!
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #149 on: July 18, 2011, 10:59:47 pm »
Going from 4 1/2 Digits to 5 or even 6 Digits  will increase the complexity dramatic.
........
So keeping 4 1/2Digits resolution would increase the possibility of success of an open source Multimeter

I agree. Trying to increase resolution places high demands on every aspect of the design. Voltage reference, clock jitter, PSRR, Analog noise etc etc...

However I think we have some advantages here compared to the commercial guys. Open Source multimeter will likely be an evolutionary project. There will be many iterations and refinements. By and by it will get better. Another advantage that we have is that we don't have to worry about profit margins and product placement. Therefore we can use (hopefully justified) pricier components.

What worries me is that no designs popped out yet. It is like all of the more experienced guys prefer to just watch and keep quiet. As if they are afraid of criticism or something.
 

Offline Fox

  • Regular Contributor
  • *
  • Posts: 54
  • Country: de
  • Electronics Engineer
Re: Open Source Multimeter
« Reply #150 on: July 18, 2011, 11:16:22 pm »
Oh i have a design for my own 5.5Digit Meter project almost finished (about 70% i guess, most of the digital stuff has to be done),
but i am not sure if meets the 5.5Digits resolution criteria and its still a bit in the flow, so i won't share it just yet.
A closed Switch should have zero Ohms or less!
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #151 on: July 18, 2011, 11:41:08 pm »
I didn't mean to offend you or something  ;D

Hope it turns out good.
 

Offline Fox

  • Regular Contributor
  • *
  • Posts: 54
  • Country: de
  • Electronics Engineer
Re: Open Source Multimeter
« Reply #152 on: July 19, 2011, 12:05:43 am »
No offense taken
A closed Switch should have zero Ohms or less!
 

Offline Zad

  • Super Contributor
  • ***
  • Posts: 1013
  • Country: gb
    • Digital Wizardry, Analogue Alchemy, Software Sorcery
Re: Open Source Multimeter
« Reply #153 on: July 19, 2011, 12:56:13 am »
It is one thing to draw what you want, but another thing entirely for it to be physically possible. For example, consider how much volume a typical meter uses for voltage and current switching, including the precision film resistor packs and 10A current shunts. Add to that a data isolation and PSU, conditioning and ADC. Now consider that on the drawing shown so far, they have to fit in <10 cu. cm.

With ADCs you can always integrate readings and filter digitally, allowing the user the opportunity to offset speed for precision. If a user is looking for spikes, then they are highly unlikely to be interested in ultimate precision.

Here is a graph of some investigations I made into the performance of some fast 24-bit TI ADCs. Noise free 20 bits (6 digits) at 100SPS is perfectly achievable, but note that this is purely the performance of the ADC, without any conditioning, protection etc.



HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #154 on: July 19, 2011, 01:54:47 am »
It is one thing to draw what you want, but another thing entirely for it to be physically possible. For example, consider how much volume a typical meter uses for voltage and current switching, including the precision film resistor packs and 10A current shunts. Add to that a data isolation and PSU, conditioning and ADC. Now consider that on the drawing shown so far, they have to fit in <10 cu. cm.

Man if it takes space it takes space. Make it 300 cm3 and worry about miniaturizing it later.


With ADCs you can always integrate readings and filter digitally, allowing the user the opportunity to offset speed for precision. If a user is looking for spikes, then they are highly unlikely to be interested in ultimate precision.

Here is a graph of some investigations I made into the performance of some fast 24-bit TI ADCs. Noise free 20 bits (6 digits) at 100SPS is perfectly achievable, but note that this is purely the performance of the ADC, without any conditioning, protection etc.

If we can get 20 bit resolution out of a 24 bit ADC, does that mean that we have an error budget of 4 bits? Or maybe it is not that straightforward. I need to figure out how to stack up these errors...

 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #155 on: July 19, 2011, 02:37:01 am »
Open Source multimeter will likely be an evolutionary project. There will be many iterations and refinements. By and by it will get better.
Another excellent reason for a modular design. Whether it's a eurocard form factor or something new, a modular design will allow for cheaper upgrades and modifications.

I gave SketchUp a try. It may actually be one of the easiest to use 3D apps I've ever encountered. Yeah, it feels tedious and clunky at times, but much less so than other software. Sorry... No buttons, LCDs or connectors yet.


That's an 18650 cell by the way.
« Last Edit: July 19, 2011, 02:45:42 am by bobski »
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #156 on: July 19, 2011, 02:58:15 am »
Glad to see SketchUp catching on  :)

What is the orange box made of, plastic or aluminium?
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #157 on: July 19, 2011, 03:13:22 am »
Plastic would be much lighter and provide better impact protection, so I guess I'll go with that. Some metal hardware is probably in order though... Those dovetail rails for the modules could be a weak point if they're just plastic.
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #158 on: July 19, 2011, 03:48:07 am »
There are a few things to bear in mind when designing for plastics. If you want to get more serious about this better read  about "designing plastic parts" on google.

What remained in my memory from my design class is

- Uniform sections - Basically you want all your walls the same thickness, otherwise they warp when they cool.

- Mold draft - You need some angle of slope so that your part can come out of the mold.

- Parting line - Basically you pick two opposite sides of a part. All surfaces of that part must be clearly visible from one of these surfaces. You will need to change the orientation of your battery compartment. Otherwise the manufacturers will hate you (and bill you accordingly).

- Minimum part count - molds are obscenely expensive. No less than 10000$ a pop.

These things will improve your designs a lot.
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #159 on: July 19, 2011, 08:44:08 pm »

Okay, I'll stop now. ^_^
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #160 on: July 19, 2011, 09:15:35 pm »
Good job. It looks a lot better.
 

Offline Zad

  • Super Contributor
  • ***
  • Posts: 1013
  • Country: gb
    • Digital Wizardry, Analogue Alchemy, Software Sorcery
Re: Open Source Multimeter
« Reply #161 on: July 19, 2011, 10:48:37 pm »
Glad to see SketchUp catching on  :)

What is the orange box made of, plastic or aluminium?

Would you touch the case of a aluminium housed multimeter when it was measuring mains voltage?  :o

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #162 on: July 19, 2011, 11:00:11 pm »
Would you touch the case of a aluminium housed multimeter when it was measuring mains voltage?  :o

PXI stuff has metal panels and sits in a metal case. Apparently it is safe.

Amateur stuff? Not sure, it depends.
 

alm

  • Guest
Re: Open Source Multimeter
« Reply #163 on: July 20, 2011, 08:24:50 pm »
Most commercial bench meters have a metal case. No safety issue as long as the case has a solid ground connection, and of course the front-end is fully floating and well isolated. I wouldn't use metal for a meter that can run on batteries, however, since you can't guarantee a ground connection (like those bench scopes with battery option that some people use without the mandatory ground connection for anything but SELV). Most commercial bench meters with battery option also used a plastic case I think. It is possible to make double isolated equipment with metal cases, plenty of consumer gear is. But you would need double the clearance and creapage distances as appropriate for the voltage rating.
 

Offline gregariz

  • Frequent Contributor
  • **
  • Posts: 545
  • Country: us
Re: Open Source Multimeter
« Reply #164 on: July 20, 2011, 08:27:36 pm »
Most commercial bench meters have a metal case. No safety issue as long as the case has a solid ground connection, and of course the front-end is fully floating and well isolated. I wouldn't use metal for a meter that can run on batteries, however, since you can't guarantee a ground connection (like those bench scopes with battery option that some people use without the mandatory ground connection for anything but SELV). Most commercial bench meters with battery option also used a plastic case I think. It is possible to make double isolated equipment with metal cases, plenty of consumer gear is. But you would need double the clearance and creapage distances as appropriate for the voltage rating.

If your clumbsy like me you'll often be dropping your meter in the wrong place. Plastic is good when that place has some voltage.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 15807
  • Country: gb
  • 0999
Re: Open Source Multimeter
« Reply #165 on: July 21, 2011, 05:39:37 pm »
I don't see why there's lots of contaversy over a hand-held meter with a metal case. It's perfectly safe, as long as there's sufficient insulation between the live parts and case and it's mechanically robust enough to withstand being thrown around and stamped on. A good metal case should be stronger and safer than any plastic cause.

 

Offline Bored@Work

  • Super Contributor
  • ***
  • Posts: 3933
  • Country: 00
Re: Open Source Multimeter
« Reply #166 on: July 21, 2011, 06:20:08 pm »
I don't see why there's lots of contaversy over a hand-held meter with a metal case. It's perfectly safe, as long as there's sufficient insulation between the live parts and case and it's mechanically robust enough to withstand being thrown around and stamped on. A good metal case should be stronger and safer than any plastic cause.

And is a risk on a workbench or near / inside a dangerous machine, where the case could cause a short circuit. And if you hold that instrument the moment you cause the short circuit with the case, your body could become a significant part of the circuit.
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #167 on: July 21, 2011, 06:25:07 pm »
If your clumbsy like me you'll often be dropping your meter in the wrong place. Plastic is good when that place has some voltage.

I see your point. metal case is not good for hand held equipment.
 

Offline Conrad Hoffman

  • Super Contributor
  • ***
  • Posts: 1420
  • Country: us
    • The Messy Basement
Re: Open Source Multimeter
« Reply #168 on: July 22, 2011, 05:49:59 pm »
My POV may not be anybody elses, but here it is anyway-

This is 2011. We have capabilities they didn't have back in the '60s. We might want to think not in terms of traditional dedicated test equipment like DVMs, that have been around forever, but something much more flexible. I collect used test equipment and even with all the stuff I've got, I can't make the measurements I (or my customers) need at a price I can afford. The world is awash in DVMs and even the junk ones are surprisingly good. 6 1/2 digit meters with HPIB are no problem, new or used. Ditto frequency counters. What I'd really like is a black box having a synthesizer chip (Analog devices has some great ones), several DVM type measurement channels (at least 2), a phase detector in hardware, some internal impedance standards and a USB interface. Maybe a counter, but not sure.

Why?

Because all that stuff can be configured not only as a DVM, but as a VAW meter, an LCR meter, a network analyzer, an audio analyzer, a signal generator and perform pretty much any bench test or component test you might want. Under PC control (IMO it has to have open software) I could configure it for whatever needed to be done, like swept measurements. I have no interest in a display, other than the PC, but a lot of interest in data-logging. Note that almost all design work in the commercial world requires data-logging.

Before you get the idea that this is a huge or complicated effort, look at the high level parts you can get today. The synthesizer chip solves that problem. There are phase detector solutions. Instantaneous voltage and current measurements give you the VAW meter function. It's a big design, but not nearly as difficult as it would have been a decade ago.

Take a look at the $16,000 Agilent E4980A LCR meter. Once you lose the display there's no reason that can't be done for a hobbyist price. With the right software you have a network analyzer (I've done this). Now look at something like the watt meters and stuff from Clarke-Hess. That functionallity shouldn't be tough to include.

I realize I've gone completely OT here, but IMO pursuing another DVM, regardless of features, will never give ROI commercially, and I can't imagine any DIY builder bothering with it. OTOH, I've been wrong before- just ask my wife!

Best,
Conrad
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #169 on: July 22, 2011, 06:20:28 pm »
Welcome aboard Mr. Hoffman,

I am so happy to see you here. Your ideas are most most definitely welcome.
In fact it never dawned on me that this thing may include a synthesizer.



PS: I received your mail. But since you are here how would you feel about posting your magazine articles (or links thereof) under your own name?
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #170 on: July 22, 2011, 06:34:15 pm »
From what I've read so far, the circuits for measuring inductance and capacitance values are both based on applying a sine or other fluctuating signal to the component and measuring its reaction. Making that signal source more dynamic and available for other functions makes perfect sense to me.
 

Offline Conrad Hoffman

  • Super Contributor
  • ***
  • Posts: 1420
  • Country: us
    • The Messy Basement
Re: Open Source Multimeter
« Reply #171 on: July 22, 2011, 06:42:38 pm »
Hi,

Sure, these are ancient but everyone is certainly welcome to read my Mini-Metrology Lab articles here. That's how things were done in the good old days. Feel free to wander the rest of the site- should be something there for just about anybody.

On the multi-function meter gadget, I don't know why nobody has done this before. All the hardware is practical, but the big players keep making their very expensive traditional instruments. Heck, the most desirable low frequency network analyzer is about $40k. Put the right package together and you might have a very desirable moderate volume product.

BTW, the key to LCR is the phase detector. Phase is your loss, and converts to esr, dissipation factor or however else you want to express it.

Best,
Conrad
 

Offline nullsmack

  • Newbie
  • Posts: 1
Re: Open Source Multimeter
« Reply #172 on: July 22, 2011, 08:08:45 pm »
Have you guys ever seen this: http://mondo-technology.com/super.html? It squeezes quite a bit of functionality into something handheld size.
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #173 on: July 23, 2011, 04:40:06 am »
It squeezes quite a bit of functionality into something handheld size.
Now you've got me thinking about gutting my Mastech pen multimeter again.
 

Offline KuchateK

  • Regular Contributor
  • *
  • Posts: 78
  • Country: us
Re: Open Source Multimeter
« Reply #174 on: July 23, 2011, 06:11:41 am »
Ideas presented by Mr. Hoffman are great.

I'm looking around for something above multimeter capabilities and much smaller and cheaper than existing alternatives for labs/professionals. Generator, LCR, capabilities that super probe has. Small, flexible multichannel replacement for three multimeters that are sometimes required and with logging capability that would allow automatic testing or graphing what is really happening over time. Such programmable device with open firmware would be great and I think there is huge market for that. Consider cost of two/three good multimeters with PC connection.

Hobbyist working on project can't really justify spending thousands of dollars on lab equipment and professionals would love lab on the go.

I was recently looking for LCR meter with ESR and this is just amazing how expensive they are. I can get Rigol scope for that price. It was much cheaper to replace all caps in the device than to hunt broken ones.

Bobski's modular project looks great, but that amount of plastic would require significant tooling cost and is not really hobby friendly. I can't imagine someone making modules for this design at home.

From hacking/modding point of view I would more likely see something that HAL-42b presented. Big PCBs for all sorts of crazy modules, big components, flexible backplane, generic off the shelf enclosures. I don't like sticking to industry standard though. Pursuing compatibility that fraction of users would utilize is huge waste of time and resources. This device should have as big microcontroller as possible with as many possible connections on the backplane as possible. Look at arduino. Minimal design compared to some alternatives. KISS rule really showed. Make it flexible and easy to duplicate.

Something to extend idea presented by HAL-42b to make it easier to get and duplicate...



I recommend Mike's videos. He is showing some nice stuff and ideas and has very little views.

Start designing circuits guys. The rest will come later. Remember! First generation doesn't have to be perfect.
« Last Edit: July 23, 2011, 06:17:44 am by KuchateK »
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #175 on: July 23, 2011, 01:22:02 pm »
Well the standards are more political than technical for me. Sticking to standards makes it a lot easier  for institutions to contribute. Imagine if we could develop a backplane akin to PXI which is open source (I know it is not literally a standard)- it would be immediate hit with all universities and research institutions. This would encourage them to develop more hardware for it, again open source, and to the benefit of us all. Btw. PXI is not a standard yet mainly because it is not fully open.

It isn't only us amateurs that need this stuff. universities and research institutions need it too. And I am not talking multimeters here. CERN just recently announced their own open source license. There are already several projects under that license, including a very nice clock signal distribution switch.  They sure have one hell of a budget, couldn't they just buy all this stuff? They could but that would have meant firing research staff, and it is not the gear that makes the science, it is the staff. The university I graduated from spent 2M$ in test and measurement equipment while I was studying there. Imagine if that could have been halved? They would have hired twice as much research staff. 

What I am saying is that standards are already out there. If we don't stick to them we have to develop our own, which is arguably impossible because we are talking hardware, not software. They make it easier to contribute to an open source project. They are already well documented - bad documentation is the plague of open source.
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #176 on: July 23, 2011, 03:58:11 pm »
Bobski's modular project looks great, but that amount of plastic would require significant tooling cost and is not really hobby friendly. I can't imagine someone making modules for this design at home.
I totally agree on the financial considerations. The project would need support from a better funded, or at least better equipped, entity. I don't envision the plastic parts being molded by home inventors. Rather, get the project producer to mold the parts and make them available as blank housings on the cheap. To further the project and get a ROI, the producer could go ahead and populate the main housing to spec and sell them along with their own module designs. That would make a standard level of functionality available for purchase with a minimum of fuss, while providing the framework for private inventor types to develop their own designs and further the project as a whole by sharing with the community.

Sticking to standards makes it a lot easier for institutions to contribute.
Sticking to standards (at least at key points in the design) makes it easier for everyone to contribute. Standards are needed if you're going to use a modular, isolated approach. Even if your end design is a physically monolithic device, keeping the circuitry compartmentalized reduces the likelihood of one functional section unintentionally influencing another. A standard set of connections at the borders of that modular isolation make it easier for people (individuals or institutions) to construct their own functional modules and cleanly append them to the core functionality of the meter. The trick is making that set of connections flexible and powerful design-wise, yet inexpensive and easy to work with.
[...] it would be immediate hit with all universities and research institutions. This would encourage them to develop more hardware for it, again open source, and to the benefit of us all.
Yes, this is what I would like to see happen. A large institution take up the cause and deal with the aspects of the design that are impractical for the independent developer to manage.

What I am saying is that standards are already out there. If we don't stick to them we have to develop our own, which is arguably impossible because we are talking hardware, not software. They make it easier to contribute to an open source project. They are already well documented - bad documentation is the plague of open source.
Impossible? I suppose if you want to develop a standard from the electrical and timing parameters up, that's a pretty daunting and expensive task. I don't see why that would be necessary here. There's plenty of existing hardware standards that can be pulled into the project design quickly and easily to create a project-specific standard.
For instance, the input modules on my design. One would obviously need power and ground connections, preferably isolated since we're doing measurements. An analog return line or two might be good... They could be multiplexed with the lines from other modules and fed to a central high quality ADC if the designer doesn't include one in the module itself. Since noise would be a problem on those analog lines, a shielded (coax?) connector of some sort is probably in order. Digital control and data lines of some sort are probably a good idea. SPI and/or I2C maybe?
Throw in some module dimensions and standard connector locations and you have a hardware standard.
 

Offline KuchateK

  • Regular Contributor
  • *
  • Posts: 78
  • Country: us
Re: Open Source Multimeter
« Reply #177 on: July 25, 2011, 04:49:15 am »
Even fancy multimeters are not using anything more than MSP430. This is processing power for SPI, I2C, RS232/485 level.

The standard for such multimeter should describe boards with specific size and connector on the edge that has I2C, SPI, RS232/RS485 (and some other) interfaces and a as much as possible control digital/analog pins. Something that requires more power than some cheap 8-32 bit MCU can handle will scare people off any involvement and development.

To be popular it has to be cheap. When it is popular then it is much easier to create high speed/fancy variations. I'll go back to Arduino as example. It became popular, because initial investment was ATmega8 with crystal and rs232 to a PC. Right now you can also get Arduino running ARM chip and it still works.

We should hit and aim at hobby/student/small business market. Guys with Arduinos that want to measure ESR/power or inductance without spending hundreds of dollars on few multimeters. It should be small modular and customizable (!) companion for cheapest Rigol scope and nothing beyond that.

Even if the tool won't satisfy CERN, it may be great for thousands of students. CERN? They have staff and money to do whatever they want (sometimes) beyond our imagination. We should leave them alone. We should focus on the other end of the market. Beginers trying to learn. When students will start to use something, then institutions will be forced to use it. They have tight budgets and they would love to have cheap open source educational tools.

In my opinion it would be easier to start small and get support from agile companies such as Sparkfun than big slow moving institutions with grants that are nicely distributed between big market players.
« Last Edit: July 25, 2011, 06:19:54 am by KuchateK »
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #178 on: July 25, 2011, 08:47:47 am »
KuchateK
I follow what you say and I agree with most of the points you make. In that light, there are some concerns that arise. Supposing that we develop an arduino shield voltmeter, I am certain that any kid picking up this voltmeter will stick it into the mains first thing out of the box. We rally can't sell this thing without at least CAT II safety. Therefore we will have to provide it in a box. Who is going to pay for certification? What will happen if somebody really gets hurt? In the country I live in, if you screw up, that's your own damn problem. If you stick an arduino shield into the mains that just means you're being stupid, you've got nobody to blame. But that's my country and that's the way I like it. Europe and US are not like that so we have to figure out how to sell this thing without causing mortal danger and legal issues to ourselves. This is the state of mind I'm in right now.

OTOH developing an arduino shield voltmeter is a quick and dirty way of getting into it, so maybe exactly the reason why we should do it. There are posts on this thread that discuss the theories of measurement in depth and breadth yet no schematics came forward. Maybe it is time to leave the scalpel and get the ax.

 

Offline KuchateK

  • Regular Contributor
  • *
  • Posts: 78
  • Country: us
Re: Open Source Multimeter
« Reply #179 on: July 25, 2011, 03:18:00 pm »
Americans have this stupid idea that if something happens you can blame everyone except idiot who got hurt and his parents that they did not teach him list of "don't do this". Should we care? Hell no!

What can we do to prevent accidents?

If we won't write some warnings then we are to blame (a little). But every mains voltage kit I did had nice paragraph about safety and that is enough for normal people around the world. We are not going forcing anyone to use it.

I think it should be a kit, not a complete product. Then you don't have to bother about some safety issues and certifications. We should not even bother providing enclosures or parts. There are many sources for that. PCBs distributed by some people would be sufficient in my opinion. Good documentation/tutorials plus code is still time consuming. Someone can create kits and distribute them later...

Should we create Arduino shields? NEVER! This form factor begs to be unsafe when it comes to any higher voltages. And I don't really think useful multimeter can be made on (even big) shield.

But... We should use Arduino as a base. As a coding platform and interface to real world it is great. Why? Because you can jump to C or assembly when you need to in any section of your code. Changing default MCU configuration and taking full advantage of its capabilities is easy. If controller would take Arduino code, then we have customization and easy development covered. Arduino would be great connector between some first boards and computer during initial design. We can later jump to ARM or something more powerful, and because they ported Arduino libraries, code can be reused.

There is one more question that needs to be answered. Should we create mains voltage multimeter? Why not make first versions going up to 50V like an oscilloscope? Want to measure something higher? You know what to do :)

I wrote about analog pins on the board connector, but after some consideration, I think that boards should be as independent as possible with something smart built in. Some digital interfaces only providing ready to read data. Without many connections you can then shield them and isolate cheaply.

For example RS485. You have ability to connect multiple boards and external devices (programmable power supply for example). It is popular industry standard and it is quite fast on short distances and can work kilometer away. Microcontrollers are cheap and every board could have some bits without sacrificing cost that much. A chain would connect to a controller that would only handle data display/logging and user interface to modules after querying them what they are. PC would do the same even through terminal. It should be also easy to provide wireless modules for boards.

Seems that there would be need for some clocking signal from controller to each board so they can be synchronized. My knowledge is rather limited and someone having more experience with more complicated measurement gear should write about how they usually work.
« Last Edit: July 25, 2011, 03:58:32 pm by KuchateK »
 

Offline KuchateK

  • Regular Contributor
  • *
  • Posts: 78
  • Country: us
Re: Open Source Multimeter
« Reply #180 on: July 25, 2011, 03:56:08 pm »
here are posts on this thread that discuss the theories of measurement in depth and breadth yet no schematics came forward.
Unfortunately I cant contribute more than talking right now. For me analog circuits are mostly spaghetti ;) Don't be shy people. Show us something.
 

Offline Extech

  • Contributor
  • Posts: 15
  • Country: us
    • Planet Extech
Re: Open Source Multimeter
« Reply #181 on: July 25, 2011, 05:01:50 pm »
I wanted to do a case design for a kick starter video, and i would like people to tell me what they think of the case so I can make it look as good as possible.

Well I think that I am looking at one Gossen range switch,
plus the bottom of the Fluke 28II painted red, with out the holster, and a bit more square !!  :)

Well I have a tip for you,  you are in a good path, but you have to surprise us !!
Yes SURPRISE US !!

Its hard to happen,  but if you are serious in what you do, it will not be that difficult.   
If you like to know what to avoid ?  Look at Extech.   ;)

Nice!  :'(  :'(
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #182 on: July 25, 2011, 05:20:44 pm »
Nice!  :'(  :'(
Haha... Meter snobs? ^_^
I have an Extech as my primary meter. I wish it had a bar graph, but otherwise it seems to be a perfectly good instrument. Fluke and Agilent meters look nice, but as an EE student (when I bought it) I couldn't justify the price: 2-3x that of the Extech for the same feature set.
« Last Edit: July 25, 2011, 05:22:15 pm by bobski »
 

Offline Conrad Hoffman

  • Super Contributor
  • ***
  • Posts: 1420
  • Country: us
    • The Messy Basement
Re: Open Source Multimeter
« Reply #183 on: July 25, 2011, 06:31:29 pm »
Here's an example of how a clever start up could take the big companies to the cleaners-
http://cp.literature.agilent.com/litweb/pdf/5990-7778EN.pdf

IMO, they totally blew it with the limited frequencies. With a synthesizer and good interface it would be a killer product, but they probably thought if they did that it would compete with their expensive stuff.
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #184 on: July 25, 2011, 09:32:02 pm »
 

Offline bobski

  • Contributor
  • Posts: 36
  • Country: us
Re: Open Source Multimeter
« Reply #185 on: July 29, 2011, 07:50:53 pm »


In case anyone wants to fool with it themselves:
http://dl.dropbox.com/u/9882625/openMeter%20Sketch%20V2.0.skp
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #186 on: July 30, 2011, 09:14:58 am »
Mr. Hoffman

What is involved in putting a synthesizer on board? Can you point to example chips/schematics? Also what new capabilities will that add?

I think this is a new idea to most of us so you may need to bring us up to speed.

Cheers
 

Offline Conrad Hoffman

  • Super Contributor
  • ***
  • Posts: 1420
  • Country: us
    • The Messy Basement
Re: Open Source Multimeter
« Reply #187 on: July 30, 2011, 08:54:16 pm »
Hi,

What you're looking for are Analog Devices DDS (direct digital synthesis) chips. It used to be simple, but now they have a huge family of them. I'd start by looking at AD9838, which is a simple waveform generator with an I2C interface. They even have the AD5933, which is a complete waveform generator and ADC designed for impedance measurements. Unfortunately it's aimed at higher frequencies and they say it only goes down to 100 Hz. This page would be a good place to start looking at all that's available. BTW, some of them don't even cost that much.

IMO, once you include a signal source in your device, all sorts of possibilities open up because you can then characterize both active and passive stuff (filters, amplifiers, caps, inductors and resonant circuits). You can also use it as a stand-alone signal generator and meter (because of course you'll build in a decent 5+ digit meter and true rms circuit).

People have gone in this direction before to some degree. Look up the Keithley Source-Meters. Too specialized and too expensive for most. The Agilent LCR meters I mentioned earlier IMO could have been much more, but they probably didn't want to drain sales of their more expensive products. The closest thing is a good PC sound card with a program like Visual Analyser, but the signal output from sound cards is less wonderful than they'd have you believe.

Best,
Conrad (my dad is Mr. Hoffman!)
« Last Edit: July 30, 2011, 08:58:52 pm by Conrad Hoffman »
 

Offline Conrad Hoffman

  • Super Contributor
  • ***
  • Posts: 1420
  • Country: us
    • The Messy Basement
Re: Open Source Multimeter
« Reply #188 on: July 31, 2011, 05:16:51 pm »
Just to babble a bit, I've no idea how to package this thing- other people here are way better at that. Standards are nice, but can make the physical hardware costs very high. I remember Eurocards, with high pin count on the connectors, but also high backplane costs. There are "NIM bins", Nuclear Instrument Modules, but I don't remember much about that format, only that it was reasonably narrow. No doubt there are many other modular standards. Or, you can put everything in a single box. With a single PCB and all connectors on that single PCB, costs would probably be lowest.

I imagine the basic functions to be 3 major user blocks. First you have a DVM module. Next you have another DVM module that can also be set up to measure current. Third, you have a source (synthesizer signal generator) module. So maybe the box has 3 sets of leads- bananas, BNCs or whatever. So far, pretty simple and just an enhanced DVM.

The key is that the input modules are all fast ADC, feeding a "brain" (either internal CPU or external PC) instantaneous data. Now, with voltage and current, you easily get DC power- that's a no brainer. But it doesn't work for AC. However, if you do instantaneous voltage and current, that does work for AC. So now you have a proper (and high $$ value to the customer) VAW (volt-amp-watt) meter.

Add the signal source, plus the ability to measure instantaneous voltage and current, and you complete the picture, being able to excite the DUT (device under test) and measure its transfer function and impedance at any frequency. IMO, the instrument should work from DC to about 1MHz to be useful.

Hopefully that defines/explains things a bit better.
« Last Edit: July 31, 2011, 05:22:33 pm by Conrad Hoffman »
 

Offline Zad

  • Super Contributor
  • ***
  • Posts: 1013
  • Country: gb
    • Digital Wizardry, Analogue Alchemy, Software Sorcery
Re: Open Source Multimeter
« Reply #189 on: August 01, 2011, 10:17:11 pm »
I'm slowly developing an LCR meter using the AD5933 (see my blog) and it is a pretty good chip in general, but It does need driving from a divider (or another DDS) if you want to lower the minimum frequency, and you need to buffer the drive signal (preferably with variable gain and offset) if you want to measure below 200 ohms or so.


Offline AndyM

  • Newbie
  • Posts: 1
  • Country: gb
Re: Open Source Multimeter
« Reply #190 on: August 23, 2011, 10:15:52 pm »
I've been reading this thread whilst on my holiday (bored without my bench and soldering iron!!).
Whilst an attempt to adhere to standards is understandable I have to say that the simplest construction would be preferable.
As for the front and back panels, I have used FrontPanel Express for many of my projects and I find them to be reasonable (especially for one off panels) and they give a very professional finish.  They even have a range of enclosures that I have also used.
A bench meter with additional functionality as detailed by Conrad gets my vote with a single main PCB and separate pcb's for mounting the external connectors or perhaps wiring the connectors from the front panel down to the PCB.  I don't want it too big (perhaps something similar in size to the HP3478 would be good).  I'd like it to be portable but not permanently so (how about some rechargeable AA's internally and a power brick when used on the bench).
The potential is vast.  It would be great to be able to replace a transistor tester, LED tester, DVM, SigGen etc., etc. with a single instrument.
Love Dave's idea about the thermal probes as I built alot of vacuum tube stuff and often look at the temperature of transformers, chokes and valves.
The synthesis core might also allow characteristics to be plotted when testing semiconductors.

Have I gone too far?????

Andy
 

Offline House91320

  • Regular Contributor
  • *
  • Posts: 176
Re: Open Source Multimeter
« Reply #191 on: September 13, 2011, 01:26:44 am »
Just some updates on whats happening with the meter (yes the project didn't just die out). i am currently working on the rev1 of the pcb. As it stands now its going to have a mono glcd, fram or eeprom (the code and board will allow you to chose), usb slave and host (the reason for the host is to be able to plug a usb flash drive in, should mention host and slave are iso to 5kv), and its a it can display and log 2, v channels and 2, A channel + a lcr channel. Any thing more you would like to know just shoot me a question.
 

Offline silversteam314

  • Newbie
  • Posts: 1
Re: Open Source Multimeter
« Reply #192 on: January 07, 2012, 05:09:05 pm »
I just read a blog post about this somewhere and came to check what has happened since Dave talked about this on the vlog.
Is there any progress, or is this project now at a standstill?
 

Offline Bored@Work

  • Super Contributor
  • ***
  • Posts: 3933
  • Country: 00
Re: Open Source Multimeter
« Reply #193 on: January 07, 2012, 06:03:56 pm »
I just read a blog post about this somewhere and came to check what has happened since Dave talked about this on the vlog.
Is there any progress, or is this project now at a standstill?

It was never a project. Dave was very clear about it that he was only doing the sketch for fun. And as you can see from the discussion here, it degraded to what always happened with such ideas. Lots of people coming up with their wishes in the hope that they find someone to do the actual work. Those doing some work quickly find out that it is really hard work and that there is little reward doing this.
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #194 on: January 07, 2012, 08:44:19 pm »
Actually this thread inspired me to do something entirely different but still along the lines of open source hardware.
I am hoping to spill my meager beans soon.
 

jucole

  • Guest
Re: Open Source Multimeter
« Reply #195 on: April 22, 2012, 09:29:29 pm »
Hi, this is the sort of thing i'd go for, it's called the Multimogger (Multimeter / Logger); I actually missed out the function generator out, so you have to imagine that's in there too. These could available in different widths allowing for more (expensive) or less (cheaper) features.



The case is simple no-frills, no display either, all that is done in software on the smart device. One thing I thought might be nice was triggers, so i included two outputs, these would be dependent on specific user defined parameters or events. For example when temperature / voltage or current etc on channel X reaches / falls etc Y  then trigger output 1 or 2. You could set it up in the UI like a typical logic analyzer trigger steps, did i tell you it had a I2C bus viewer in there too? (maybe phase 2 ;-)

The UI software logic would handle most of the clever display and control stuff allowing for a minimal hardware specification for each channel plugin (shield?)

All communication is done via bluetooth with the idea it works in conjunction with a smart device or a laptop. 

Also it's got to be really nice and heavy, filled with lots of batteries, I don't want something to slide across the bench every time I hook things up to it.

It's the swiss army knife of multimeters!! and it's putting the MULTI back into multimeter! ;-)


Kind Regards

Jules


 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #196 on: April 22, 2012, 11:13:23 pm »
You mean something like this?



I've been working on mechanical aspects it for a while. It is a very useful concept except all the difficulties in making it actually work ::).
« Last Edit: April 22, 2012, 11:18:55 pm by HAL-42b »
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 33122
  • Country: au
    • EEVblog
Re: Open Source Multimeter
« Reply #197 on: April 23, 2012, 02:25:23 am »
I've been working on mechanical aspects it for a while. It is a very useful concept except all the difficulties in making it actually work ::).

Those pesky minor details!  ::)

Dave.
 

jucole

  • Guest
Re: Open Source Multimeter
« Reply #198 on: April 23, 2012, 09:16:39 am »
You mean something like this?

hehe. Now that's just weird! did you sneak into my room while I was asleep claiming to be Darth Vader from the Planet Vulcan and download my thoughts with an 80's Walkman to the sound of Eddie Van Halen?


There seems to be lots of ideas and drive to build such a device, does anyone know of any websites that allow people to contribute to hardware projects in the same way as Sourceforge does for opensource software? if not would sourceforge be a place to start?
 

HLA-27b

  • Guest
Re: Open Source Multimeter
« Reply #199 on: April 23, 2012, 11:29:53 am »
There seems to be lots of ideas and drive to build such a device, does anyone know of any websites that allow people to contribute to hardware projects in the same way as Sourceforge does for opensource software? if not would sourceforge be a place to start?

No such place yet afaik. Actually I'm not sure I've seen a strong collaboration on any OSHW project yet, let alone the need to lower the participation threshold.
The community does not know yet how to handle collaboration when the item in question is an actual physical object to be sold for profit. There is no unit of measurement for contribution.
 

Offline slateraptor

  • Frequent Contributor
  • **
  • Posts: 833
  • Country: us
Re: Open Source Multimeter
« Reply #200 on: April 23, 2012, 03:29:59 pm »
You mean something like this?
...
It is a very useful concept except all the difficulties in making it actually work ::).

LMFAO!! :P
 

jucole

  • Guest
Re: Open Source Multimeter
« Reply #201 on: April 24, 2012, 04:11:29 pm »
No such place yet afaik. Actually I'm not sure I've seen a strong collaboration on any OSHW project yet, let alone the need to lower the participation threshold.
The community does not know yet how to handle collaboration when the item in question is an actual physical object to be sold for profit. There is no unit of measurement for contribution.

I stumbled on a Kickstarter project which are developing a sourceforge site for openhardware, which can be found here http://www.kickstarter.com/projects/373493158/open-hardware-needs-a-sourceforge-of-its-own  They actually got their funding too, and this is the site they are building https://opendesignengine.net/ - looks a little like a dog's dinner, but it might be promising. They are sponsored by a Mac30 http://mach30.org/  Mac30 are looking into opensource space flight!! So. you never know in a few years time you might well be traveling out on a flight on your holiday, and hear "Good afternoon, welcome aboard the Airbus openhardware beta release flight ...." ;-)


 

Offline danielpublic

  • Newbie
  • Posts: 3
Re: Open Source Multimeter
« Reply #202 on: May 04, 2012, 05:59:13 am »
First post, so Hi there!

Woke up about three hours ago with an idea (who knows when that one comes around the bend again..) and spent time doodling in FreeCAD (its FLOSS with a great community & rapid dev.) till an half hour ago I saw dealextreme shipped my multimeter.

Whereupon I thought: "Oh, hey... wonder if there is an opensource multimeter out there?"
Then I slapped my forehead mosquito-hard... well I should of thought of that maybe before I ordered it >:(, especially as I have a lifelong crush on the (free) open source realm.

I'll read the thread in a bit and look for some general pcb etc dimensional measurements. Cool to just fiddle with it in the mentioned CAD application and then print it with my RepRap.

Anyhow, what I'd use it for other than the usual:

  • Would be really cool if I could learn about electronics, breadboard tuts. so forth.
  • Would be very Nice to etch a pcb then supply a list measure between x+y and then chirp happily at me and err but most of all simple trouble shooting and generate a LOG that I could share with the wise folk. ('HI GUISE')

I mean... image a easily diy home etched reprap pcb, soldered, powered and tested with one device. Now that would deserve the seal of approval. err... of course maybe not soldered with the multimeter that... could one probably develop a halfassed thrown together from a fdm-hotend if needed.
« Last Edit: May 04, 2012, 06:05:32 am by danielpublic »
 

jucole

  • Guest
Re: Open Source Multimeter
« Reply #203 on: August 09, 2012, 05:59:17 pm »
My friends and I have been developing an open source multimeter. I wanted to do a case design for a kick starter video, and i would like people to tell me what they think of the case so I can make it look as good as possible.

Hi, just wondering if you've managed to make any progress on your project?

regards
 

Offline poorchava

  • Super Contributor
  • ***
  • Posts: 1649
  • Country: pl
  • Troll Cave Electronics!
Re: Open Source Multimeter
« Reply #204 on: August 10, 2012, 09:38:16 am »
I think that cost is one of the less important issues. Since this is open hardware, you can expect people to want to build it on their own. For example they can buy bare PCB and then assemble those. If for example they don't want/need/can't afford LCR measurement (eg. because of expensive IC used in it) they simply don't assemble this module. Simple as that.

Another approach is to offer a 'motherboard' assembled (containing MCU, power management, display control, comm interfaces) with some 'standarized' pinout connectors. Connectors would need to carry isolated power supply, comm bus (RS485?+some paralell). Then every individual module would be an add on with obvious possibility of building your own module even on breadboard.

I think that this is an approach that would allow to sell kits to biggest group of people, because everyone could find an affordable configuration and possibly upgrade later. That way people from poorer countries (like myself) could easily contribute to the project while you would still be able to sell fully assembled and full-featured version to people who can afford those.

The opnly problem is that it would take significant amount of system and software engineering to make whole system configurable and scalable, but it's definitely doable.

As for the enclosure, for sure custom shapes are a dead end. Tooling for industrial methods of production (like injection molding) is extremly expensive and in most cases a minor mistake in design means that you need to pay this tooling fee once again. I like the idea of extrusion-based enclosure designed for Eurocard size pcb. 100x160 is actually a plenty of space to implement stuff (I'm generally a type of pervert who like to cram as much stuff on smallest area of pcb possible - i just feel that abusing pcb space is an unnecessary waste :D)
I love the smell of FR4 in the morning!
 

Offline crispus

  • Regular Contributor
  • *
  • Posts: 126
  • Country: ro
Re: Open Source Multimeter
« Reply #205 on: September 18, 2012, 02:55:54 pm »
Hi guys,

In these 15 pages there a lot of things that should contain a DMM. I think for sure that analog front-end is one of common subsytems.

My analog knowledge is limited. Does anybody volunteers to design analog front-end?

Has anybody some good readings about designing analog front-end? What are the pitfalls? What should contain? What shouldn't?

Thanks.
I know I'm numskull, but I look around me and I feel better.
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #206 on: March 05, 2013, 08:50:02 pm »
Hi Folks,

first post on this forum, so: Hi all  :)

Sad to see that this nice idea has not been updated in quiet some time. I'd really like to contribute to a open dvm project...so why don't we get started on this one  ;)

How about getting some basic high-level requirements done and fixed to reanimate this topic? Here are my recommendations:

1. Modular Design: AFEs with a central medium micro, let's say a STM32F4 (done some nice stuff with this one; plenty of computing power, nice peripherals, etc. )

2. For most of the proposed functions, we need to accurately measure VDC (Ohm, Amps, VDC, VAC, not so sure about the LC-Stuff). I think it may be possible to achieve 6 x/x digits (somewhere around 2999999 counts, around 22 noise-free bits).
2.1 Guess it would be a good idea to go with a custom integrating adc. I'd suggest a multi-slope design (first up multi-slope rundown, not sure if we need continuous runup). This     would give us decent speed with a nice accuracy. After all, an integrating adc isn't that hard to do...
2.2 The controller and auto-ranging would be implemented in an FPGA (Xess offers some cheap Spartan-6 LX25 modules), presumeably at a speed >50Mhz for the integrator time base.
2.3 Add decent protection circuits on the input, to comply with some CAT rating
2.4 Decade (bought) resistor network for 5 switchable ranges: 200mV, 2V, 20V, 200V, 2000V
2.5 Make sure that the buffer in front of the ADC is reasonably high quality (noise isn't that much of a problem for an integrating adc, if it's designed properly)

3. With the DVM capability, we could then build additional building blocks for current measurement, resistance (with precision current source), etc.

4. Figure out how to do VACrms. If the adc is fast enough - do it in software. Otherwise, use a COTS component (sorry, aerospace term here  ;D) or build the circuit (nope, don't want to do that  :o)

5. Of course bench-type one. No handheld.

I'll go ahead and do a sys-architecture drawing the next days for the VDC front-end with the basic modules.

So long,
Stoney
 
« Last Edit: March 05, 2013, 09:02:21 pm by Stoney »
 

Offline crispus

  • Regular Contributor
  • *
  • Posts: 126
  • Country: ro
Re: Open Source Multimeter
« Reply #207 on: March 06, 2013, 02:43:05 pm »
Hi Stoney. Welcome.

I'm interested,  but I lack in analog.
I think that a modular approach is the best because it gives anyone the freedom of choice.
Analog front-end is the common part of any multimeter. Can you do it? :D
I know I'm numskull, but I look around me and I feel better.
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #208 on: March 07, 2013, 12:58:15 am »
I'm also not quite THE expert yet...I'm more into embedded computing for airborne use, but I've done some fairly complex PCBs (6 layer+, BGAs, High Speed, etc.) with no more than 2 revisions, so I guess I'm not that stupid after all...my hope is to get a guru to have a look at the schematics once they're done to give some negative feedback  ;) Based on the requirements, I'm going to: First up, high-level block diagram and split the work. Second, do modular building blocks people can work on "independently" and put their unique knowledge into...to make it better than I ever could...  :)

There are some crucial building blocks, but with todays parts, its getting easier every day to do precision stuff. But, as I said, we have to get the requirements right and establish a baseline to work on. With the modular design in mind, I would add another requirement:

6. The mesurements are streamed to a PC for display purposes, and mode selection is done there. Just to keep the interface out of the equation for the initial phase. Once the AFE is done and working, we can attach what ever interface people want to the modular µC-Board.

Glad to see someone is still interested :)
« Last Edit: March 07, 2013, 01:00:41 am by Stoney »
 

Offline crispus

  • Regular Contributor
  • *
  • Posts: 126
  • Country: ro
Re: Open Source Multimeter
« Reply #209 on: March 07, 2013, 09:02:00 am »
Here is a nice diagram for bench multimeter:
http://www.ti.com/solution/digital_multimeter_bench_system
I know I'm numskull, but I look around me and I feel better.
 

jucole

  • Guest
Re: Open Source Multimeter
« Reply #210 on: March 07, 2013, 09:56:15 am »
I'm working on a DMM with some interesting features;  I'm using some DMM chipsets;  once i have a proof of concept and if it's worthy of a show'n'tell I'll post it here.

 

Offline crispus

  • Regular Contributor
  • *
  • Posts: 126
  • Country: ro
Re: Open Source Multimeter
« Reply #211 on: March 07, 2013, 11:57:36 am »
Using DMM chipsets is not somehow limiting?
I mean, if you need only basic/supported functions it's OK, but if you want to do something customized, it that possible?

I think I would like more a discrete ADC.
I know I'm numskull, but I look around me and I feel better.
 

jucole

  • Guest
Re: Open Source Multimeter
« Reply #212 on: March 07, 2013, 12:40:25 pm »
Using DMM chipsets is not somehow limiting?
I mean, if you need only basic/supported functions it's OK, but if you want to do something customized, it that possible?
I think I would like more a discrete ADC.

A while back I was messing with my cheaper DMM; I pulled up the chipset datasheet and had a look though;  what I realised was in the datasheet they give the basic circuit for each aspect of the DMM;  which made it even more achievable for a beginner like me, I was quite excited.  But after I made up a pcb in my head all I had was just another DMM clone using the same chipset as the rest.  I did a bit more reading and after looking through some more the latest chipsets I found something I thought was really interesting; and that is some of the new ones offer 2 wire I2c.  Which means it can be controlled directly through software!  so to me that opens up massive possibilities;  for example the UI need not be rotary switching and buttons; it could be touchscreen;  you could calibrate it in software using offsets.  But what if you did use a screen, rotary and buttons etc in a board shape that exactly fitted the shell of any existing DMM;  "pimp-my-meter" ?  ;-)

Edit: the other idea I had was to only use 2 input jacks and use software switching; and the other really crazy ideas; you'll have to wait and see ;-)
« Last Edit: March 07, 2013, 01:00:25 pm by jucole »
 

Offline crispus

  • Regular Contributor
  • *
  • Posts: 126
  • Country: ro
Re: Open Source Multimeter
« Reply #213 on: March 07, 2013, 01:02:22 pm »
What chipset do you use? Are they available on European market?
I tried to find some time ago, and I saw only Cyrustek chips. But those aren't available on tme or farnell...
I know I'm numskull, but I look around me and I feel better.
 

jucole

  • Guest
Re: Open Source Multimeter
« Reply #214 on: March 07, 2013, 02:12:29 pm »
I have some Cyrustek ES51990.  http://www.cyrustek.com.tw/spec/ES51990F.pdf   
The problem is I don't really do electronics, so I could do with some help if anyone is interested - I make no promises about completing this though, it's just a proof-of concept.  The specs for the DMM would be basically as the datasheet;  It would need a uC with quite a bit of program space as most of the interesting features will be done in the code - which is where I can help;  the only requirement is that all work is opensource and uses opensource tools to create it.

 

Offline kripton2035

  • Super Contributor
  • ***
  • Posts: 2089
  • Country: fr
    • kripton2035 schematics repository
Re: Open Source Multimeter
« Reply #215 on: March 07, 2013, 03:10:10 pm »
I have some Cyrustek ES51990.  http://www.cyrustek.com.tw/spec/ES51990F.pdf   
The problem is I don't really do electronics, so I could do with some help if anyone is interested - I make no promises about completing this though, it's just a proof-of concept.  The specs for the DMM would be basically as the datasheet;  It would need a uC with quite a bit of program space as most of the interesting features will be done in the code - which is where I can help;  the only requirement is that all work is opensource and uses opensource tools to create it.
how did you get these chips ? I asked cyrustek some time ago for samples and they told me this chip is only for lcr manufacturers
they didnt gave me any more information than the ridiculous facts in the datasheet ...
if you dont have anything more than this datasheet we cannot do any chip interface ???
sorry I read the datasheet it is far more complete than the one we had some times ago
something can be done, but if the chip is unavailable to hobbysts this will not be very usefull ...
« Last Edit: March 07, 2013, 03:22:53 pm by kripton2035 »
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #216 on: March 07, 2013, 03:17:38 pm »
Here's a DVM the guys at the TU Berlin built in one of their lab courses. 5 1/2 digits and reasonably precise, even tough they use a simple approach. http://www.emsp.tu-berlin.de/fileadmin/fg232/Lehre/MixedSignal/Dateien/Digitalvoltmeter/Schaltplan_DVM.pdf.
« Last Edit: March 08, 2013, 10:24:57 am by Stoney »
 

Offline kripton2035

  • Super Contributor
  • ***
  • Posts: 2089
  • Country: fr
    • kripton2035 schematics repository
Re: Open Source Multimeter
« Reply #217 on: March 07, 2013, 03:31:50 pm »
another sorry from me. you talk about the ES51990
I was refering to the ES51919/ES51920 which datasheet is very poor.
 

jucole

  • Guest
Re: Open Source Multimeter
« Reply #218 on: March 07, 2013, 04:18:41 pm »
how did you get these chips ?
Every wannabe EE has his sources but If I told you my source; it would no longer be my source! ;-)


something can be done, but if the chip is unavailable to hobbysts this will not be very usefull ...
Yeah, very true. (wack!! goes the last nail into my open DMM idea coffin, lol! );
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #219 on: March 08, 2013, 08:34:15 pm »
I just finished the block diagram....

In term of Collaboration on this Project, what would you choose? I like to start the project on the http://www.ohwr.org/ (CERN) with the CERN OHL version 1.1. The page is on chilli-project, which will give us a nice and handy issue tracking system and the possibility to include VC-repositorys, a wiki, etc., etc.

EDIT: Or should we just go with github?
« Last Edit: March 08, 2013, 09:13:07 pm by Stoney »
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #220 on: March 08, 2013, 10:10:10 pm »
I'd say github. But basically just pick whatever works for you best. You're doing the work, so you get to pick what's easiest for you. :)

Also, thanks for your sensible contributions to this loooong thread. :) So far everything you posted looks actually practical, so I am looking forward to seeing what you come up with!  :-+
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #221 on: March 09, 2013, 02:51:52 am »
The github repo is online at: https://github.com/Stoney49th/OSHW-Multimeter

Feel free to stop by  :D I welcome everybody to join and spread the word...hope to get some feedback (issues work great  ;) ) from u guys :) Maybe we can actually build this thing and make another really great piece of open source hardware :) I wont be able to do it all by myself...so help is always welcome and appreciated!

See you on github  8)
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #222 on: March 09, 2013, 03:28:41 pm »
Couple of quick random thoughts while going over the documents:

ADS1258EVM is a nice ~ EUR 50 board that can get you up and running quickly with some decent resolution measurements. It's no integrating multi-slope adc because it's a delta-sigma adc. :P But it is affordable and reasonably easy to integrate so you have an easy starting point.

Yay! You picked spartan-6. All for it, and I might be able to contribute a bit there. The multi-slope adc + fpga combo has my interest for an entirely different non multi-meter project. Just make sure you're using (system) verilog and everything is dandy from my rather egotistically motivated standpoint. :P

stm32f407 as mcu ... again all for it. :) Use that quite a bit now for current projects.

regarding block diagram and ETH PHY on the right side of galvanic isolation ... ethernet has the added bonus of isolation, which IMO why it's a nice and easy interface for DIY measurement gear where 1) you want some safety and 2) don't want to have think too hard. I'd say aim for 100 MBit. For control alone you can probably suffice with 10 Mbit, so if the ONLY goal is commands over ethernet just do 10 mbit. But 100 MBit is easy enough with the stm32, and it gives you a nice bit of bandwidth to pump samples over to the PC in exchange for not too much effort. And yeah yeah, you can do gbit, but then you want to connect the gbit PHY to the spartan-6. Anyways, 100 mbit with a decent tcp stack on the stm32 will get you nice capabilities.

Integrated PSU ... if the amperage allows, try to make it a seperate daughter PCB that you can plonk on the main PCB. That way you can reuse it in other designs, and design improvements go both ways. I see this being done in both the DIY and the industrial sphere. In fact, I am just starting to do this myself. Design a couple of PSU blocks once, and then you can use it in different designs without reinventing the wheel. Plus it makes prototyping a lot faster if you can just grab a ready to connect PSU block and plonk it on the pcb/breadboard/deadbug.

Voltage ref ... try and make use of the fact that quite a few hobbyists would like an affordable lab standard. If you can define it such that the voltage ref is both usable in your design and as a standalone reference it would help the design effort. But at the same time, if this feature adds too much work for you ... skip it! Don't fall for the trap of wanting to do everything at once. It's a bit of a trade off. If making it a seperate module is hardly any effort, I'd say do it. If it is a significant effort ... screw those guys (and this guy :P ) and their need for a lab standard. Keep it simple. Now that I think about it ... screw those guys by definition. Keep it simple. First revision should be made with as major goal Just Get Something That Works. So keep in the back of your mind you may want to seperate the reference as a module, but that's about it.

And luckily your focus is a bench DMM, and not one of those Rule The World (and thereby defeat the Chinese) handheld opensauce multimeters that frollic in the pasture side by side with pixies and unicorns. A DIY bench DMM makes sense in 2013. A handheld does not IMO. Anyways, don't care for a "handheld makes no DIY sense" vs "bench is the way" discussion/flamewar. I am just glad you chose benchtop. Otherwise I would not even expend keystrokes/braincycles over it. :P

One more random remark that is low prio, but more as a placeholder: for commands, use SCPI. there's been some discussion in another thread about it, and IMO scpi is a reasonable choice for DIY hardware like this. At this stage I would not spend too much time on it. The main reason I mention it now is so you don't go and spend time & effort on some new way to send commands to your DMM. Just write down "[ x ] Send command & receive data from instrument. Use SCPI." somewhere on your project list. :P No need to spend more time on that right now. The analog is where the challenge is.

As for digits, I'd say aim for 5 1/2 digits for iteration #1 with an eye on 6 1/2 digits for future iterations. If you can make everything in the 6+ digit area the first go then go for it! If not, keep things simple, compromise a little and settle for a bit less accuracy. The ONLY reason I say this is to stay away from the trap of trying to be overly perfectionistic. Just get something that operates reasonably well first. After that you do incremental improvements.

Plus, I think that 5.5 digits is possible by just plonking in the previously mentioned ADS1258EVM without too much thought. :P

Anyways, enough semi-random remarks for now.
 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1799
  • Country: de
Re: Open Source Multimeter
« Reply #223 on: March 10, 2013, 12:22:48 pm »
There're a few other potentially delta-sigma ADCs for such a project:

Texas Instruments: ADS1256, ADS1672
Analog Devices: AD7190, AD7764
Linear Technology: LTC2400, LTC2440

The choice for the right voltage references is also not as easy as it seems to:

Maxim Integrated: MAX6126, MAX6325/MAX6341/MAX6350
Analog Devices: ADR44x, AD584/AD586/AD588
Linear Technology: LTC6655, LM399AH
Texas Instruments: LM399AH

At the beginning reduce the goal to somewhat around 5digits to reduce the frustration.
There is a reason why LM399AH (maybe it's more of a LM199AH) is used in 6.5digit DMMs. But it's not only the tempco of voltage reference itself but the sum of all tempcos in front of the ADC.
Always bear in mind that 6.5digits means something like 21 noise-free bits and 5.5digit still 18bits. Refer to figure 1 in AN82 for that.
A few ideas could be selected from the datasheets of HP 34401.
« Last Edit: March 10, 2013, 12:28:50 pm by branadic »
Computers exist to solve problems that we wouldn't have without them. AI exists to answers questions, we wouldn't ask without it.
 

Offline crispus

  • Regular Contributor
  • *
  • Posts: 126
  • Country: ro
Re: Open Source Multimeter
« Reply #224 on: March 11, 2013, 10:56:07 am »
...
Yay! You picked spartan-6. All for it, and I might be able to contribute a bit there. The multi-slope adc + fpga combo has my interest for an entirely different non multi-meter project. Just make sure you're using (system) verilog and everything is dandy from my rather egotistically motivated standpoint. :P
...
Why do you need a FPGA?
I know I'm numskull, but I look around me and I feel better.
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #225 on: March 11, 2013, 11:55:29 am »
Why do you need a FPGA?
Because it's cool? :P

And more seriously ... It's Stoney's design, and I was remarking on the choice of fpga in there. He wants to use the fpga to process the comparator output of the dual slope ADC as per the block diagram. All I'm saying is that I'm glad he uses spartan-6, because I am familiar with that and those are affordable in single units and you can get them in hobby friendly packages.

And as for branadic's ADC list, yeah those are some nice ones. In fact, the ADS1256 is a better choice for this sort of thing than my suggestion of ADS1258. Whatever ADC you might want to use ... just use one that for which an affordable (~ $50) dev board exists. That lowers the bar for people to join in.
 

Offline crispus

  • Regular Contributor
  • *
  • Posts: 126
  • Country: ro
Re: Open Source Multimeter
« Reply #226 on: March 11, 2013, 12:21:57 pm »
I quoted you because only you used the word 'FPGA' in topic :D

For me, it seems to be too complicated, at least for a hobby project. I will follow this, and maybe I'll took only the blocks I'm interested in.

I'm a software guy. If is anything I can help, I'll be glad to.
I know I'm numskull, but I look around me and I feel better.
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #227 on: March 11, 2013, 03:03:40 pm »
For me, it seems to be too complicated, at least for a hobby project. I will follow this, and maybe I'll took only the blocks I'm interested in.

Well, for the chosen architecture I can see why Stoney put the fpga in there. It's a cost effective way to get good timing resolution for your dual-slope adc. With as added bonus that when the hard work is done, and you decide you want more channels, that is reasonably straight forward.

That said, personally when I would do this I think I would go for using a ready made 24-bit ADC dev board and integrate that into the design for iteration numero uno. That get's you going faster. But, it's not my design, it's Stoney's design. And use of dual slope adc is perfectly reasonable, so if that has his interest (and as such will get built) then I'm all for it. :)

Quote
I'm a software guy. If is anything I can help, I'll be glad to.

Well, a good working (stm32f4) port of an scpi parser would be damn handy IMO. Both for this project and for the other OSHW thread going on. It's not as sexy as a pretty gui, but pretty gui's are a dime a dozen. A good scpi parser running on mcu is something that can really make the difference in usability IMO. As in, being able to script your measurements is damn handy!

I love being able to set up my scope over gpib, and would love to setup a DIY bench DMM with a few commands and then receive measurement results. To me for a DMM that is worth a lot more than some gui with pretty pixels.
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #228 on: March 11, 2013, 09:30:03 pm »
@flibble: Nice, I've never looked at verilog...but maybe it's time to learn something new :) It would be nice if we could fit the design in an LX9, so we don't need that nasty BGA-Chip on the board... For the PSU: Jap, I intended to make it external...it just doesn't make sense to put it directly onto the AFE if the design should be modular. Also, it would increase the PCB size significantly, so it's kind of a no-brainer. I already have some nice and tiny switching psu building blocks in altium from my previous designs, but I'll use linear regulators for the AFE (with beefy filtering) of course! In terms of Software & Ethernet: 100MBit is the way to go here, so we get decent speed....I'm not sure if we should use 1588 here, but it would make the thing more compatible to LXI, if someone is willing to implement such a large interface (I'm not  :o ).

@Delta-Sigma ADC:
Puhh, long story short: I won't use one.
After couple of hours diggin through lots and lots of datasheets from linear and analog, i found the resolution is just not enough. Most of them offer only 21.5 to 22 noise free bits in its best configuration. In addition, running on 7-15SPS is a bit low... To really achieve the full resolution of those devices, one needs a ultra low noise buffer in front of it, with variable gain (x10 for the smallest range). Designing a x10 buffer amp with noise <50nV over a decent temp-range with low drift is a very difficult task, if not impossible in some regards (its really always a trade off, one design is a bit noisier, but with better tempco, etc. etc. ). With an integrating ADC, noise isn't that much of a problem (well, of course you want to minimize it, but it's not that critical for 6 1/2, for 7-8 digits it certainly becomes deadly  ;)) if it is properly designed. We'll see how it turns out.

I haven't had much time this weekend, but I'll try and start with the detailed blocks for each module the next days. After some thoughts, the biggest problem right now for me is the range switching and the input switch in front of the integrator (for the multi-slope thing). It has to be really fast (the faster, the better...less error when the Vmes is switched out and the +-Vref is switched in) and it must not inject too much charge into the integrator. As far as range-switching is concerned, I would like to use JFETs. But this would certainly require a part with a very low leakage current (very very low). Any Ideas on this one??? One other problem is the "master switching" just after the decade resistance. If one would apply 1kV and the device is in it's lowest range, the relay has to switch the full Voltage....in other words,it has to withstand the full voltage after it has been switched of (>=1kV in this case). So a JFET is not working here. Most designs use 2-3 quality relais for the inital switch and later on route the signal with JFETs.

@FPGA: The only way to get >50Mhz counter+switchting speed for the ADC is an FPGA. I can't think of another solution, and a LX9 TQFP-1000 only costs you ~$30-$40 (28€ for me). If we're able to fit the design into 9k macrocells, it's not that expensive after all, and allows for a great deal of flexibility :)
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #229 on: March 11, 2013, 10:40:48 pm »
@FPGA: The only way to get >50Mhz counter+switchting speed for the ADC is an FPGA. I can't think of another solution, and a LX9 TQFP-1000 only costs you ~$30-$40 (28€ for me). If we're able to fit the design into 9k macrocells, it's not that expensive after all, and allows for a great deal of flexibility :)

Well, if all you need is say 10 ns time resolution at a relatively low repetition count then you can probably get away without an fpga. That said, you can get pretty damn good time resolution (way better than the 10 ns example) with the fpga. And as you said, you do get a lot of flexibility. As in: I can think of something that will get you 10 ns with less expensive parts, but it's not going to do much more than counting. Plus it won't get you to say 1 ns or below that.

Anyways, what kind of timing resolution + repetion count do you need for your dual slope adc?
 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1799
  • Country: de
Re: Open Source Multimeter
« Reply #230 on: March 12, 2013, 08:09:54 am »
Quote
Most of them offer only 21.5 to 22 noise free bits in its best configuration. In addition, running on 7-15SPS is a bit low...

You wanted to realize a DMM not a scope, right? And you have an idea about what "only 21.5 to 22 noise free bits" means? If not you better take a look at AN82 or the accuracy translator attached. I'm not sure if you realy understood the challenge of what you are going to do.

Normally those types of ADCs are ASICs and not consumer parts you can buy everywhere. Refer also to:

http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=snoa597a&fileType=pdf

« Last Edit: March 12, 2013, 11:50:48 am by branadic »
Computers exist to solve problems that we wouldn't have without them. AI exists to answers questions, we wouldn't ask without it.
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #231 on: March 12, 2013, 09:26:44 pm »
Oh sorry, seems like I forgot a simple word in my previous posts...so far, I only wrote about resolution, not absolute/relative accuracy. One of the requirements is 2000000 counts (ops, think there is still an error in the req. doc) which will require at least 21 noise free bits of resolution. Given the fact that the delta-sigmas in the other post only offer one slightly above that, and, lets say, the buffer in front of it kills another bit of resolution, the integrating adc is the way to go.

Yap, your right, I dont want to build a scope. But 50SPS (which might be a good point to start with) isn't 2GSPS. In order to do statistical mesurements, recording, stuff like that, it's the lowest minimum i can life with (ok, 100SPS on 2000000cnts would be nice, followed by 1kSPS for 200000cnts and 10kSPS for 20000cnts).

I've built a nice CAL-System for sensors used to test the structural lifetime. These sensors are currently in use for the A400M, the A380, A320. Back then (my bachelor thesis) I used a PXI-System with a 7-1/2 digit meter which was capable of 100SPS in high-res mode together with some motion controllers, precision voltage sources and so on.... The DMM had even more SPS than the max. I wrote above in 5-1/2 digit mode. Of course, the NI gear is awesome and insanely expensive, but we really used all its capabilities, which were almost the minimum required for the task (analog position sensors, really expensive and quiet precise for their underlying principle, you need good gear for that and a nice cal lab).

If you think I'm on the wrong track, show me the right one :) I'm always glad to hear different opinions and other, better and easier solutions!
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #232 on: March 12, 2013, 11:01:54 pm »
Oh sorry, seems like I forgot a simple word in my previous posts...so far, I only wrote about resolution, not absolute/relative accuracy. One of the requirements is 2000000 counts (ops, think there is still an error in the req. doc) which will require at least 21 noise free bits of resolution. Given the fact that the delta-sigmas in the other post only offer one slightly above that, and, lets say, the buffer in front of it kills another bit of resolution, the integrating adc is the way to go.

That right there!
For ease of discussion, assume for a moment that as you say the analog stuff in in front of the adc "kill another bit of resolution". As in there's a certain voltage noise source of whatever it is uV rms. You don't magically change the characteristics of the front end by swapping out the adc. So if that "kills 1 bit at 21-bits" voltage noise source is lets say 1 uV rms, then this very same 1 uV noise source is present even if you follow it with an awesome 32 bit adc.

So if you want to go and argue "but the stuff in front kills 1 bit" , then by the exact same argument this noise will kill a whole lot more of your 32 bit adc.

Anyways, if you know a good way to get those 2E6 counts at a reasonable cost go for it. But I still maintain that for a first iteration it makes a lot of sense to ease up on the requirements a bit. If only because that way THE REST of the system also can be built with components that are somewhat affordable.


Quote
If you think I'm on the wrong track, show me the right one :) I'm always glad to hear different opinions and other, better and easier solutions!

Depends on what the goal is. If the goal is a learning exercise that you and you alone are going to be doing the next year or so go for it! If you want something that is a bit more accessible to more people then you may want to ease up on the requirements. After all, if things are so super easy as maybe you hope they are ... then you will be done in no time. And hardly any effort "lost" since you made it modular, so you can upgrade parts of the design for your higher spec next iteration. That, and you can incorporate lessons learned from iteration #1.

But as said, it's your design so have at it. I'm just giving some perspective on how I'd do it.

PS: now that I mentioned it ... what is the design goal? Buildable by people of <fill in> level of skill? Build cost ..., etc... A lot of those often unwritten assumptions dictate what is reasonable and what is not...

PPS: Oh yeah, you didn't answer this one from previous post:  "Anyways, what kind of timing resolution + repetion count do you need for your dual slope adc?" The answer to that will determine the sense vs non-sense of using an fpga. Definitely since you say you are new to verilog (and presumably new to vhdl as well).
« Last Edit: March 12, 2013, 11:03:55 pm by mrflibble »
 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1799
  • Country: de
Re: Open Source Multimeter
« Reply #233 on: March 14, 2013, 08:20:19 am »
Quote
I've built a nice CAL-System for sensors used to test the structural lifetime...

Listen, it's not my goal to doubt your skills or stop you from what ever you want to develope and present in here, just go for it!

As an engineer I develope for example in the field of high resolution capacitive sensors together with my colleague. We're always at the limit of available circuits measuring down to Attofarad with tendency to Zeptofarad and also in here we are confronted with the same problems that occur in voltage references such as humidity in packages and pcbs, stress, temperature dependency etc. Having all that knowledge in my mind voltage references are a new challenge to me to get them under control. And the reference for sure is one of the major devices besides adc and the other stuff. You might know that every additional bit doubles the efforts. And I'm sure that the integrated gain stages in a modern 24bit ADC are much better as you would expect. The only way to reduce noise in here is to decrease bandwidth and cool down the stuff.

My suggestion is, keep the "stage win" as small as possible otherwise this project will change into some kind of pyrrhic victory.
Computers exist to solve problems that we wouldn't have without them. AI exists to answers questions, we wouldn't ask without it.
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #234 on: March 14, 2013, 11:26:22 pm »
No offense taken :) I just wanted to make some sort of statement that I'm not one of those "hey lets build a 10kSPS 8-1/2 digit meter for $10 and make it open source" type of guys  ;D

Well, I don't question the work of the fabulous engineers over at linear or analog, their ADCs are pretty nice. The only thing that struck me was the sampling rate...I wanted to do some sort of software-filtering after the adc to get rid of some noise and and errors and increase the resolution by some degree. I did some calculations the other day for the input buffer....and oh boy....your "decrease the bandwidth" and "double the effort for every bit" statements hold ;)
Let's just assume for a moment, one were to consider a 24-bit ADC (linear) with a decent front end. Would it be ok, if the sample rate is "only" 7-15SPS (indeed, the bandwidth of the VDC front-end itself will be very low, otherwise its very hard to keep the noise low enough)? One could of course increase the sampling rate while lowering the resolution in "streaming mode", to offer a high sample rate, for example over the (planned) ethernet interface. In terms of the update rate of a potential display connected to the µC, I'm no longer sure if a sampling rate >10SPS is really that useful for the human eye and brain. Maybe, my requirements were/are a bit optimistic and over the top right now...and the very limited bandwidth of the input stages (to achieve a high resolution) wouldn't allow for a very high sampling rate, even if resolution is sacrificed (well, we don't want to make the damn thing too complicated and expensive, right)....
The integrating adc (in the current drawing) would allow for a great deal of flexibility, in terms of sampling rate/resolution and input ranges. If we find some nice solutions, the sampling rate would also clearly be higher....but with an input stage so limited in bandwidth,  this advantage isn't that relevant anymore, at least for the "streaming mode". Oversampling on the other hand could be of advantage here...

P.S: Jap, the reference will definitely be one of the major contributors to the actual accuracy of the frontend. Would you like to do one, as a "stand-alone" modular type? Would be really great, because my knowledge about references is very, very limited and certainly not good enough to build one :palm:
« Last Edit: March 14, 2013, 11:52:43 pm by Stoney »
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #235 on: March 15, 2013, 06:41:10 pm »
No offense taken :) I just wanted to make some sort of statement that I'm not one of those "hey lets build a 10kSPS 8-1/2 digit meter for $10 and make it open source" type of guys  ;D

Hopefully you're one of those "hey lets build a 10 SPS 5-1/2 digit meter for $100+ and make it open source" type of guys. XD

Quote
Let's just assume for a moment, one were to consider a 24-bit ADC (linear) with a decent front end. Would it be ok, if the sample rate is "only" 7-15SPS (indeed, the bandwidth of the VDC front-end itself will be very low, otherwise its very hard to keep the noise low enough)?

Absolutely. If your target audience is "hobbyist that like to build some of their own test gear and are able to make reasonable tradeoffs" then I'd say a bench DMM with 5 1/2 digits that does 10 SPS would be quite nice. It would have many many uses on the bench. Sure it doesn't compete with the state of the art professional meters, but I suspect (and hope) that is not the intention.
 

Offline free_electron

  • Super Contributor
  • ***
  • Posts: 7653
  • Country: us
    • SiliconValleyGarage
Re: Open Source Multimeter
« Reply #236 on: March 15, 2013, 07:02:53 pm »
before you start arguing about what fpga to use... : go write the code for the dual slope system.
it's no much more than a few counters. you don't need a 9000 macrocell fpga. you can put it in a CPLd if you want.

the key to the slope system is the integrator / comparator. you will need to pick a REALLY good opamp and comparator. and you will need ultrastable caps and resistors around it. if you want the integrator to run fast you can get away with a small cap. try to find a silver/mica C0G/NP0 type.
use resistors with the lowest tempco you can find ( Caddock for example)

the switching balance for the current can be done using a good analog switch like a DG444, no need to muck around with jfets.
and you need an ultrastable reference.

absolute accuracy is irrelevant in this system. you don't want any drift.
i wrote multiple posts on the forum here how this system works and is implemented in HP34401 as well as how it is calibrated.
i know people that have built a 5 1/2 digit dual slope in a 64 macrocell cpld.

the number crunching is done by a cpu. yuo only need the gate array to get the runup and rundown counters since the cpu can't bitbang that fast.





Professional Electron Wrangler.
Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #237 on: March 15, 2013, 07:37:06 pm »
Regarding the fpga my point so far has been that you probably can get away without one. If all you need is ~ 100 MHz counting frequency there's simpler ways. CPLD could be one, but since there's already a STM32F4 on the BOM you can use that. Again, it depends on the (as of yet unspecified) required timing resolution.

There, fpga relegated to being a non-issue. Onward to the analog stuff. ;)
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #238 on: March 15, 2013, 07:43:37 pm »
Also ...

i wrote multiple posts on the forum here how this system works and is implemented in HP34401 as well as how it is calibrated.

do you have a link to which one you mean? Right now I'm reading https://www.eevblog.com/forum/reviews/hp34401-teardown/ but maybe you mean another thread.

edit: probably this one. reading ...
« Last Edit: March 15, 2013, 08:06:10 pm by mrflibble »
 

Offline Marco

  • Super Contributor
  • ***
  • Posts: 5168
  • Country: nl
Re: Open Source Multimeter
« Reply #239 on: March 15, 2013, 11:30:07 pm »
Silly question ... why can't you just use dithered oversampling with a fast ADC to get high resolution? (Potentially with sine or triangle wave dither, theoretically gets resolution far faster than white noise.)
 

Offline chickenHeadKnob

  • Frequent Contributor
  • **
  • Posts: 933
  • Country: ca
  • doofus programus semi-retiredae
Re: Open Source Multimeter
« Reply #240 on: March 16, 2013, 05:24:55 am »
Regarding the fpga my point so far has been that you probably can get away without one. If all you need is ~ 100 MHz counting frequency there's simpler ways. CPLD could be one, but since there's already a STM32F4 on the BOM you can use that. Again, it depends on the (as of yet unspecified) required timing resolution.

There, fpga relegated to being a non-issue. Onward to the analog stuff. ;)

May be I just don't understand but I don't think you can get 100Mhz timing resolution from STM32F4 on chip counter/timers, its more like 1 or 2 Mhz. I have been itching to find an excuse to play with those small cool-Runner PLDs. I thought of making a ballistic (bullet) chronograph but stm32 timers have enough resolution for that. Something I haven't discovered yet: what quality and stability does the dual slope clock need - Ovenised  or TCO?
 

Offline ve7xen

  • Frequent Contributor
  • **
  • Posts: 865
  • Country: ca
    • VE7XEN Blog
Re: Open Source Multimeter
« Reply #241 on: March 16, 2013, 08:11:24 am »
May be I just don't understand but I don't think you can get 100Mhz timing resolution from STM32F4 on chip counter/timers, its more like 1 or 2 Mhz. I have been itching to find an excuse to play with those small cool-Runner PLDs. I thought of making a ballistic (bullet) chronograph but stm32 timers have enough resolution for that. Something I haven't discovered yet: what quality and stability does the dual slope clock need - Ovenised  or TCO?
They may only accept a clock input at relatively low frequency (though probably at least 10s of MHz), but for an integrating DAC you need input capture mode, where the clock for the timer can be derived from the system clock, and the capture input is asynchronous. In that modes I believe the STM32F4 series can run at around 150MHz, giving you ~7ns timing resolution.

Can't comment too certainly on the clock stability, but I'd guess you want it to be as good as the measurements you intend to make. For absolute accuracy and long-term stability you probably want at least a TCXO.
73 de VE7XEN
He/Him
 

Offline chickenHeadKnob

  • Frequent Contributor
  • **
  • Posts: 933
  • Country: ca
  • doofus programus semi-retiredae
Re: Open Source Multimeter
« Reply #242 on: March 16, 2013, 09:48:56 am »

@Ve7xen and mrflibble :

My apologies    :-[ you appear to be correct, I seem  to be conflating F4 series with some other micro's spec sheet from my faulty memory. sigh -gettin old.

The advance timer at least can run at system clock rate 168Mhz. as I dimly understand it you need to drive an analog switch with hardware logic (software would be to slow) when the comparator trips, so you will still need a little off chip logic. I'll shut-up now and leave you guys to it! Still might build a basic dual slope on my own just for amusement and learn-dina'tin.
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #243 on: March 16, 2013, 04:39:12 pm »
@chickenHead:
Absolutely right. I first thought I could do the switching with the Capture/Compare peripherals (they are quite good actually) but it just doesn't make sense if one can buy a TQFP-FPGA for 30 bucks. No BGA (woohoo), and its not that expensive.

As far as the CPLD is concerned: No, you really dont need 9k cells for a integrating ADC :) But, I really want the unit to be expandable, so people can add other front-ends, for example for L, C, F, and other stuff. So it's just a nice and versatile solution :)

For the clock, I would use a FOX +-1,5ppm inital accuracy with +-2,5ppm drift TCO. They're cheap ($3-4), SMD, small and reliable (used them on quiet a number of boards, never head problems and well within specs).

The DG444 is cool, after i looked it up, i also found the ISL43681. Do you think it'll be possible to make the reference +-2,5V (with a precision divider + inverter, aka. LT1043) so we could use this one? It's much faster, with equally low leakage and charge injection but its a low voltage type (+-5VDC supply and therefore input range max.)....and I guess we'll have to switch reasonably fast to reduce the errors in the integrator.

But back to the input buffer stuff:
I found that the LTC6240 would be a good candidate here, because of its extremely low input bias/offset current and the even lower current noise. Because the input divider/protection devices will have a very high source impedance, the current noise (together with the high source impedance) plays a role in the noise performance. The main noise contributor is indeed the input divider and not the op-amp itself (if it has a low input referred voltage noise, of course). The LTC6240 has a great performance in terms of input current and noise but has one major disadvantage. The input offset voltage drifts around 0,6-1,0µV/°C. So one has to compensate that thing, for example by chopping, which leads to a hole other set of problems.
So, I've chosen the LTC1052. Equally low current noise, but higher input bias current (30pA, times 15) but significantly lower drift, noise, and offset (drift ~10-50nV/°C). The challenge here is to balance the junctions (the datasheet is quiet nice on this one, they write a lot about it). Since we basically only need need unity gain and a gain of x10 for the lowest input range (200mV, otherwise the integration time becomes too long for small signals, in other words, the error increases), a switch will bypass the divider and I'll choose a non-inverting configuration. In the unity gain feedback path, the switch will add the needed material junction so we always stick with the same number in each configuration. It's quiet critical to keep the temperature of all parts in the buffer equal, and it would be nice if the resistor values are close to each other on all paths, so cancellation occurs for the thermal/junction noises. Later on the PCB, I'll add the possibility to solder in a air-protection cap, just to make sure that no airflow can build up thermal gradients on the resistors and introduce offset drift. By default, the switching frequency of the 1052 is 330Hz, so a first order low-pass in front of the op amp will ensure that we're not running into aliasing for low frequencies, with a ~200Hz -3db point. Afterwards, the integrator will take care of it. I'll do some drawings tomorrow for the input switch, overrange limit and the input buffer and add them to the repo ^^ (nah, these modules are so closely connected, you really can't treat them seperatly  ::)).
 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1799
  • Country: de
Re: Open Source Multimeter
« Reply #244 on: March 16, 2013, 07:19:08 pm »
Quote
P.S: Jap, the reference will definitely be one of the major contributors to the actual accuracy of the frontend. Would you like to do one, as a "stand-alone" modular type? Would be really great, because my knowledge about references is very, very limited and certainly not good enough to build one :palm:

Why not resort to something like this, the SVR-T should be a good choice at the beginning:

http://www.gellerlabs.com/Voltage%20References.htm
Computers exist to solve problems that we wouldn't have without them. AI exists to answers questions, we wouldn't ask without it.
 

Offline ve7xen

  • Frequent Contributor
  • **
  • Posts: 865
  • Country: ca
    • VE7XEN Blog
Re: Open Source Multimeter
« Reply #245 on: March 16, 2013, 07:24:36 pm »
@chickenHead:
Absolutely right. I first thought I could do the switching with the Capture/Compare peripherals (they are quite good actually) but it just doesn't make sense if one can buy a TQFP-FPGA for 30 bucks. No BGA (woohoo), and its not that expensive.

As far as the CPLD is concerned: No, you really dont need 9k cells for a integrating ADC :) But, I really want the unit to be expandable, so people can add other front-ends, for example for L, C, F, and other stuff. So it's just a nice and versatile solution :)
A $30 BOM item you don't even have a use-case for? o.O
73 de VE7XEN
He/Him
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #246 on: March 16, 2013, 08:19:26 pm »
A $30 BOM item you don't even have a use-case for? o.O

Maybe he just want a moderately justifiable excuse to plonk in an fpga. :P At least that is how I interpret the "have to learn verilog" + "lack of any hard specs regarding interval timer resolution".

The only number I've seen timing wise was the "> 50 MHz counter frequency". Well, 20 ns is done easy enough with the stm32f4 as mentioned. So is 10 ns. Now with say 1 ns resolution we get into territory that it might make more sense to use an fpga. You can do all sorts of tricks to get the 1 ns with the stm32f4 again with an external prescaler yadda yadda, but in that case I think I'd choose fpga. And if you are after the 500 ps - 100 ps ballpark then suddenly fpga becomes quite effective in BOM cost + design effort, compared to other solutions I can think of.

But as said, since the only mention is of "something that counts at 50 MHz"... pffffrt, STM32F4. Problem solved.

Why not resort to something like this, the SVR-T should be a good choice at the beginning:

That's actually no bad idea at all. Sure, you might do better. But ... you might also do worse. :P And at least this is a design that has been out there for a while and should there be any quirks, you can be fairly sure there's some info out there. Info like that also has value ... something that the hobby posse sometimes forgets in their haste to add +1 to the Not Invented Here Syndrome Count.
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #247 on: March 17, 2013, 12:19:46 am »
Alright, in the meantime I've been reading some more of free_electron's (great :-+ ) posts about the multislope stuff + the HP Journal of april 1989. Damn, that multislope approach as done by HP is quite elegant.
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #248 on: March 17, 2013, 01:46:46 pm »
@FPGA stuff: lol guys, let's just wait until we have timing requirements from the integrator. Then we decide what we actually need ;)

VDC input buffer doc online (in 03_ folder). Its a very dirty dave cad, hope u can read my handwriting  ::) ....I'll do a clean one in software once it's close to final ;)

Gimme some negative feedback  ;D
« Last Edit: March 17, 2013, 01:49:03 pm by Stoney »
 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1799
  • Country: de
Re: Open Source Multimeter
« Reply #249 on: March 17, 2013, 02:23:46 pm »
Quote
...it just doesn't make sense if one can buy a TQFP-FPGA for 30 bucks...

I wonder why Agilent and Co still use their expensive hybrids in modern devices instead of a low cost fpga or cpld, if it was that easy to get a high precision integrating adc. There must be something overlocked, such as temperature dependent latency or similar effects that decrease the real resolution.

Quote
For the clock, I would use a FOX +-1,5ppm inital accuracy with +-2,5ppm drift TCO. They're cheap ($3-4), SMD, small and reliable (used them on quiet a number of boards, never head problems and well within specs).

Attached you find the specifications for a TCXO series of actcrystals. They have made me a bunch of TCXOs with customer specific frequency in another project. It's not an OCXO but very good for that price.

There are some other ADCs that are interesting:

CS5534 24-Bit A/D Converters with Ultra-Low-Noise PGIA
http://www.cirrus.com/en/products/cs5531-32-33-34.html

PRI5610 Präzisions - 26 Bit - ADC
http://www.ohh.de/5610.htm

ER-ADC150 programmable 24-bit integrating A/D converter
ER-ADC180 programmable 26-bit integrating A/D converter
http://elbertresearch.com/users/editorialdisp.php?mn=110669&fn=standardProducts

Particularly the last link matches the requirements for such a project and is a "ready to use" device.
« Last Edit: June 28, 2014, 04:56:03 pm by branadic »
Computers exist to solve problems that we wouldn't have without them. AI exists to answers questions, we wouldn't ask without it.
 

Offline free_electron

  • Super Contributor
  • ***
  • Posts: 7653
  • Country: us
    • SiliconValleyGarage
Re: Open Source Multimeter
« Reply #250 on: March 17, 2013, 09:49:22 pm »
Quote
...it just doesn't make sense if one can buy a TQFP-FPGA for 30 bucks...

I wonder why Agilent and Co still use their expensive hybrids in modern devices instead of a low cost fpga or cpld,

fluke uses cyclone fpga's. so do the tek rebranded flukes.

the reason agilent uses those asics is because they have their own waferfab. they can !
that asic was designed many years ago and also does other things besides the logic section of the multislope system. ( display controller , digital isolation link , memory decoder etc. )
Professional Electron Wrangler.
Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline Marco

  • Super Contributor
  • ***
  • Posts: 5168
  • Country: nl
Re: Open Source Multimeter
« Reply #251 on: March 18, 2013, 12:01:56 am »
I don't think it's possible to get a comparator fast enough to make a FPGA worth it ... if you want decent offset you're looking at something chopper stabilized and those aren't exactly fast.
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #252 on: March 18, 2013, 12:32:16 am »
Regarding comparators, I think Stoney currently has an LT1016 on the list. That's going by the fact that the datasheet is in the git repo. ;)

I also had a look at that one and compared it to the LT1011 (from the TU Berlin design). Personally I am not yet convinced LT1016 would be better than LT1011 in this application. It does have 1 big thing speaking for it, and that is that the propagation delay has been characterized over temperature. A nice flat 10 ns over temp for the falling output. No such spec to be found for the LT1011. On the other hand the LT1016 has a worse max offset (3.5 mV) than the LT1011 (0.5 mV), and the max offset drift for the LT1016 is not even mentioned. Or at least I couldn't find it. The typical offset drift is the same (4 uV/C) for LT1011 and LT1016.

And as bonus the LT1016 has a differential output, but that's more of a nice to have, not a must IMO.

As for comparator speed, if I understand the dual slope/multislope thingy correctly, you don't care overly much about the speed. As long as it's fast enough. The main characteristic with this sort of low repetition rate zero crossing detector is not so much speed, as it is variations in the propagation delay. For all I care it has a whopping 100 ns prop delay, as long as it is bang on 100 ns over all conditions. It is uncertainty in prop delay that is annoying because that translates into uncertainty of amount of accumulated charge. It's a similar problem to offset voltage, just a different axis. And the slope at which the zero crossing occurs dictates which of the two is the more annoying problem. ;D

This all of course is still assuming I understand the design properly (big if XD).
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #253 on: March 18, 2013, 07:21:48 pm »
Uhm, well, I just had a look at the datasheet and thought it might be a good point to start from, no special intentions on using THIS specific comparator....we'll see how it turns out once I can make some calculations on the delay/switching delay/speed/clock/timing of the integrator.
The opamp in the integrator is also very critical...it has to be quiet fast, but low drift and low input current/offset current as well! Input "leakage" current into the opamp will introduce errors directly in the runup so should be avoided, and the slew rate comes into play when the voltages are switched for the runup/rundown phases. This is also a limiting factor for the slopes of the rundown, together with the timing resolution and the resulting under/overshoot for the steepest rundown-slope. Low drift is obvious, thou not ultimately critical, since I will null and offset compensate the integrator after each measurement or at a specific rate if the drift allows for it. But still, drift within one measurement cycle should be reasonably low. This will of course depend on the temp. rise, but with a standard, fast opamp, i think the drift is going to kill us. I remember some fast "precision" AD opamp with 50V/µs (the 8-1/2 digit wizards built their own with 100V/µs) wich might be a good candidate...

Anyone had a look at my (very crappy) drawing of the input overrange / VDC buffer stuff yet? I expect plenty of stupid mistakes so please correct me!
« Last Edit: March 18, 2013, 07:24:26 pm by Stoney »
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #254 on: March 18, 2013, 08:42:52 pm »
Anyone had a look at my (very crappy) drawing of the input overrange / VDC buffer stuff yet? I expect plenty of stupid mistakes so please correct me!

I didn't quite follow R5, R6 (near note [9]). This is stil purely input signal conditioning + protection, yes?

If so, why the R5/R6 combo in T912 package there? As in what's the intended function of that LTC1052. I follow things right up to the + input of the LTC1052, and then I don't quite follow your intention.

Don't you just want a boring unity gain buffer amplifier at that point?

Also, don't you want the "To VAC" after you do some buffering with said boring unity gain buffer?

you range switch it, you low pass it, clamp it, and then you x1 buffer it. No x1/x10 precision resistors required so far, unless I am missing a clever trick you have up your sleeve.

 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1799
  • Country: de
Re: Open Source Multimeter
« Reply #255 on: March 18, 2013, 08:53:33 pm »
Quote
The opamp in the integrator is also very critical...

Seems like you haven't watched the posted link (AN-260 A 20-Bit (1 ppm) Linear Slope-Integrating A/D
Converter), as this critical part was already faced there and how it has been solved (page 5-6, A2-A3):

http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=snoa597a&fileType=pdf

« Last Edit: March 19, 2013, 07:31:22 am by branadic »
Computers exist to solve problems that we wouldn't have without them. AI exists to answers questions, we wouldn't ask without it.
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #256 on: March 19, 2013, 02:04:28 am »
While we're at it ... possibly something like this for the comparator stage:

edit: reduced size of pic...
« Last Edit: March 19, 2013, 02:10:14 am by mrflibble »
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #257 on: March 19, 2013, 09:24:44 am »
Hm, the x10 gain would be useful in the lowest range to keep the integration time and get the signal over the leakage introduced errors within the integrator. Otherwise, you would have to integrate ten times longer in the lowest range (200mV FS) to keep the resolution.

I wanted the Vac to be protected by the same overrange protection as the Vdc, otherwise another pair of diodes, more diode leakage, more resistors, etc. I thought about the aliasing error stuff and decided to use a simple first order filter after the initial, "high frequency" filter :) . Maybe, a active second order one with the 1052 could be better, but since the sampling rate will be reasonably low, I don't think we run into problems here. Of course, you don't want a 200Hz -3db bandwidth for the Vac stuff, so it will have it's own buffer, presumably switchable with a small smd reed switch (the meder ones are quiet cool, low EMF, and reasonably priced (4€, don't know the dollar price)).
« Last Edit: March 19, 2013, 10:19:38 am by Stoney »
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #258 on: March 19, 2013, 05:05:29 pm »
Hm, the x10 gain would be useful in the lowest range to keep the integration time and get the signal over the leakage introduced errors within the integrator. Otherwise, you would have to integrate ten times longer in the lowest range (200mV FS) to keep the resolution.

Ah okay. In which case I'll keep it simple and just use a boring unity gain stage there. Especially since for iteration 1 I can live with the longer integration time. And for iteration 2 I am secretly eyeing a multi-slope approach. And in both cases at this point it's a simple buffer without any variable gain.

 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #259 on: March 20, 2013, 09:53:33 pm »
Yep, and after I started thinking about the actual integrator configuration, I realized that one can perfectly adjust this with the "integration resistor"  :palm: So no stupid switchable gain, just a simple unity gain buffer...
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #260 on: March 20, 2013, 10:42:29 pm »
Heheh, that was my reasoning as well. ;) With the change of making it just a unity gain buffer I suddenly agree with the schematic for the most part. :) I'd do the RC filters a bit different, but that is a minor detail that can be worked out later. As long as we can agree on the fact that the "To ADC" has been low pass filtered, clamped and buffered.

Oh yeah, and I would just kick out the auto zero switch near note [10]. Personally I plan to do auto zeroing around the integrator. Definitely not in this input stage, unless I am missing something...
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #261 on: March 20, 2013, 11:32:19 pm »
Hm, how would you do the filter? Maybe your solution is better ;) (active?)

The autozero should, in my opinion, include the input buffer. Maybe it's placed somewhat wrong...if I would place it just behind the diodes ( between clamps and R4), one could use a low-voltage MEDER one (much, much cheaper than those bloody expensive coto ones and equally low emf). The auto-zero in front of the buffer is certainly not equal to the "each cycle integrator zero" but can be used if requested by the user to really zero the whole unit including the (temperature drifted, its certainly useless if used 2s after power-on) input buffer. The integrator is of course part of the procedure. I'm not really sure if a real auto-zero can be achieved (or makes sense) without grounding the input buffer input...
« Last Edit: March 20, 2013, 11:59:53 pm by Stoney »
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #262 on: March 21, 2013, 12:35:09 am »
Hm, how would you do the filter? Maybe your solution is better ;) (active?)

Well, I don't know about better, but it is even simpler. :) It's passive just like yours. Only difference is that I would only use 1 RC stage, and I would use a slightly different f-3db. Remember that the "we shall use low loooow bandwidth" was from the part of the discussion where delta-sigma ADC was also on the table.

In the meantime I've read a bit more about dual-slope, and I have seen the error of my delta-sigma ways. ;) Dual slope is damn nice in many ways. So I want to try and make a 5-1/2 digit dmm based on dual slope. Not because it makes economic sense, but as a fun learning exercise. If it was to make economic sense I'd better work a bit and buy something on ebay. Definitely more time-efficient than building one. But building one is more fun efficient!  ;D

I would use a single RC filter and limit it to somewhere in the 1 kHz - 10 kHz range. And I'd do that at the point where you have your 100 kHz RC filter. And then I would leave out the 200 Hz Rc filter. Why? Well, lets not forget that our trusty integrator is an integrator. You know, one of them low pass filtery thingies.

In any event, it's not really worth too much discussion. You can put them both on the PCB layout and then make it an optional component fit. You would for example keep your 100 kHz + 200 Hz arrangement, and I would do 5 kHz + passthru. And depending on results we can simply change component values a bit after the initial measurements.

Quote
The autozero should, in my opinion, include the input buffer. Maybe it's placed somewhat wrong...if I would place it just behind the diodes ( between clamps and R4), one could use a low-voltage MEDER one (much, much cheaper than those bloody expensive coto ones and equally low emf). The auto-zero in front of the buffer is certainly not equal to the "each cycle integrator zero" but can be used if requested by the user to really zero the whole unit including the (temperature drifted, its certainly useless if used 2s after power-on) input buffer. The integrator is of course part of the procedure. I'm not really sure if a real auto-zero can be achieved (or makes sense) without grounding the input buffer input...

I'm not entirely convinced I'd want an autozero there. My focus is to keep everything boringly simple for a first go. So if it is a Nice To Have, and not a crucial bit of circuitry ... out it goes! Maybe I will see how it is an advantage when I see it in context with the rest of the circuit.

 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #263 on: March 21, 2013, 10:12:23 pm »
K, I'll leave it in there for now, with the two stages, one can basically run a number of combinations or just put a simple solder bridge in there. Same for the auto-zero, I'll leave it in there as an option  :) Since no other complaints came up, I would call the input conditioning done for now ;) except for:

Let's talk CAT-Protection and over-voltage protection (not overrange, thats already done :P) to finish the voltage input section 8)

I'd love to have CAT-II (for measuring mains stuff), which would be rated 1kV (withstanding 6kV input impulses if I remember it correctly ^^ ).  I don't have access to a 61010-1...but I could certainly use the DO-160 Class 5 as an equivalent :D (just kidding). Maybe someone could post a quick wrap-up what the unit needs to survive in terms of energy and pulse duration....
Littlefuse offers some nice gas-discarge tubes wich might do the job, with low capacitance and certainly no other leakages during normal operation: http://www.littelfuse.com/products/gas-discharge-tubes/high-voltage-gdt/cg3.aspx.
My fist try would be to put a high wattage resistor after the GDT to absorb the energy once it arcs over, together with a fuse in series with the resistor after the tube, to stop the "magic-smoke-and-fire generator" if it fails (obviously sacrificing the unit, but hey, you just managed to blow the protection :) ). I really wouldn't like to see a PTC in a "precision" instrument (all that temperature compensation stuff, and a PTC in the input path?!). But maybe one could use one in series with the high-wattage R instead of the fuse to cool down the current in a constant overvoltage condition, which might be a better idea after all instead of the fuse. I've actually never used a GDT before...so, what do you think? Any chance this arrangement could do the trick? Do we need some additional "constant high energy overvoltage, eg. plug the damn thing in your 5kV generator" protection?

So long,
Lukas

Edit:  :palm: I guess I wrote some BS up there regarding the idea for the protection....basically, It wouldn't do anything to protect the unit...I'll leave it in the thread as a bad example:D
« Last Edit: March 21, 2013, 10:25:47 pm by Stoney »
 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1799
  • Country: de
Re: Open Source Multimeter
« Reply #264 on: March 21, 2013, 11:04:19 pm »
What about something like the circuit shown in AN-D16 "High Voltage Protection" by Supertex?

www.supertex.com/pdf/app_notes/AN-D16.pdf

BTW, updated my post concerning ADCs:
https://www.eevblog.com/forum/oshw/open-source-multimeter/msg203717/#msg203717
« Last Edit: March 23, 2013, 02:36:47 pm by branadic »
Computers exist to solve problems that we wouldn't have without them. AI exists to answers questions, we wouldn't ask without it.
 

Offline mrflibble

  • Super Contributor
  • ***
  • Posts: 2034
  • Country: nl
Re: Open Source Multimeter
« Reply #265 on: March 21, 2013, 11:56:24 pm »
I don't know enough about doing a "proper" CAT-II protection, while still maintaining high precision. So if you guys come up with something reasonable I'll be happy to copy that and learn from it. XD In the absence of that my plan is to not measure mains with this thing because I don't care about measuring mains in any high precision. I have my cheapo handheld for that. ;)
 

Offline Stoney

  • Contributor
  • Posts: 19
  • Country: de
Re: Open Source Multimeter
« Reply #266 on: March 25, 2013, 08:10:38 pm »
@banadic: Hm, interesting... the http://www.supertex.com/pdf/app_notes/AN-D11.pdf has some more details on that... and btw, nice ADCs :) Basically a off the shelf multislope thing...might be a good fallback, but I suspect them to be insanely overpriced  :P

@flibble: I certainly don't want my unit with these nice and expensive components and a costly PCB blow up into magic smoke, just because I was too lazy or too stupid to design a proper protection ;D And hey, a protection is simply a must have...one can certainly argue about some, more or less optional, features but not about the protection...

The standard fluke input protection that dave explained in one of his videos (If I remember it correctly) would be a good point to start from...some (most?) of the fluke bench meters are protected CAT I 1kV, CAT II 600V (which means a 4kV impulse protection http://www.ni.com/white-paper/5019/en). And I guess they also use the R-Thermistor-MOV combination on their higher precision bench type multimeters (posted in another thread here in the forum: http://headsplosive.com/2011/11/fluke-8846a-6-5-digit-multimeter-teardown/). Any idea which type/brand they use for the PTC? The MOVs look like standard ones, with the high-wattage R in series with the PTC...Seems like they also used some R's to distribute the voltage equally between the series MOVs there...

Anyone here who did a HP/Agilent/BK/NI/Keithley...etc. teardown and has some insight into their input protection?? The old HP ones seem to use the GDT/Fuse/R's combination in most models...

Tektronics/Fluke 8808: http://s222.photobucket.com/user/Zadpics/media/Tektronix%20DMM4020%20Bench%20Multimeter/Fluke-Input-Protection.jpg.html?sort=4&o=5 Seems like some MOVs + maybe GDTs (??)

Keithley 2000: http://bardagjy.com/?p=1167 Also a MOV/GDT combo with presumeably a PTC (the orange thing I guess) and a series R...
« Last Edit: March 25, 2013, 09:32:46 pm by Stoney »