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 workA 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.
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.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 workA 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 DMM seems pretty pointless as I can't see what you can do better/cheaper than what's already out there.
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.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.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 workA 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 DMM seems pretty pointless as I can't see what you can do better/cheaper than what's already out there.
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!
Well that rules me out! :'(.
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.
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.
There's the Nano, a crap open source 'scope so why not do the same thing with higher spec' hardware?
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.
So am I! I have trolled all over the forum! Sorry.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!
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.As I understand it it's a kickstarter project.. he's looking for finance.
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.
Exactly my point. See my first post :DAs 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?
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 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.
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.
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 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.
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.
Battery life is very important in a hand held meter, beware.
Dave.
The battery is going to be user replaceable.
A DIY DVM kit is priced high than an equivalent fully assembled and warranted junk Chinese DVM.
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.
tft color screenDon'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
Quotetft color screenDon'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.
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.
-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)
My video suggestion is rendering now as the next blog!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.
But here is the DaveCad sketch!
Dave.
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)
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.
This is about Dave's multimeter:
...
For Bluetooth / Zigbee / whatever you can use a removable module to save some money on the initial cost.
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)
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.
Output jack for programmable current, function generator or power supplyWhile 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.
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.
Bluetooth/Zigbee for wireless secondary display or PC/Phone interfaceAgain, 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.
Two 5-digit displays for V/A/W/AC etc. Three would be nice, but adds complexityRight 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?)
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...)
Does decent LCR/ESRSure.
Power display/power factor
Voice outputEww! 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.
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.
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...
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.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 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.
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%.)
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.
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
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.
Why not use the standard channels in voltage configuration for temperature sensing?
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.
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!
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.
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%.)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?
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?That assumes the project creators have a realistic idea of costs.
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...
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 forgot to mention. Bench instrument cases are available off the shelf
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.
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.
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.
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 (http://en.wikipedia.org/wiki/Kickstarter)
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.
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.
With D cells you could possibly create a killer battery life logging meter, opening up new niche markets.
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
For the display nothing beats VFD's in terms of readability. I really like my Agilent 34401A7-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.
so please stop posting nonsense like all this...
Quickest sketch took me 20 min...
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...
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.
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.
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.
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.
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.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, 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.
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.
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.
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 ...
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.
This is why software piracy is not really stealing.
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.
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.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.
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?
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.
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.
Well, I'd like to hear what you think
Awesome Job! What CAD software is that?
Hello there, first post on the forum...
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?
...However, it isn't exactly very hacker friendly...
...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.
Hello there, first post on the forum...
You win the first post of the year award!
Awesome.
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.
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.Problem is that there is very little inside to hack & the build quality is crap! Non starter sorry :-\
B.R.
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.
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.
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.Interesting, so you don't want too many customers because it increases support costs.
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.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.
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.
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.
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.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?
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:
This would turn the open-meter into a set of standards…
A proposed Starting spec[/li]
- 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 (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
[/list]
This could serve as a module in some of the fancier setups, but without this basic functionality, you've got nothing. Check
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.
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.
USB power would require at least one isolated DC-DC converter, more if you want multiple channels. Probably not worth the complexity IMO.
A proposed Starting spec
- 4 1/2 digit resolution Make that 6 https://www.eevblog.com/forum/index.php?topic=4087.msg55214;topicseen#msg55214 (https://www.eevblog.com/forum/index.php?topic=4087.msg55214;topicseen#msg55214)
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.
........
So keeping 4 1/2Digits resolution would increase the possibility of success of an open source Multimeter
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.
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.
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
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.
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.
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.
It squeezes quite a bit of functionality into something handheld size.Now you've got me thinking about gutting my Mastech pen multimeter again.
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.
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.
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! :'( :'(Haha... Meter snobs? ^_^
Okay, I'll stop now. ^_^I lied.
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?
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 ::).
You mean something like this?
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?
You mean something like this?
...
It is a very useful concept except all the difficulties in making it actually work ::).
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.
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.
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 have some Cyrustek ES51990. http://www.cyrustek.com.tw/spec/ES51990F.pdf (http://www.cyrustek.com.tw/spec/ES51990F.pdf)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
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 ?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! );
...Why do you need a FPGA?
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?Because it's cool? :P
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.
@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 :)
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...
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.
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!
I've built a nice CAL-System for sensors used to test the structural lifetime...
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
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)?
i wrote multiple posts on the forum here how this system works and is implemented in HP34401 as well as how it is calibrated.
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?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.
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:
@chickenHead:A $30 BOM item you don't even have a use-case for? o.O
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
Why not resort to something like this, the SVR-T should be a good choice at the beginning:
...it just doesn't make sense if one can buy a TQFP-FPGA for 30 bucks...
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).
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,
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!
The opamp in the integrator is also very critical...
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.
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...
Thanks! I did a bit more reading, and looks like metallized polypropylene film is the ticket. So for example Vishay MKP1837 or MKP1840 series.
As far as I now the better choice is polystyrene and even better is a teflon type capacitor. Last one is for sure expensive:What expensive cap? All I see is an audioph00l website with an overpriced cap. Doesn't mean that the cap we will actually use is going to be super expensive.
http://www.soundlabsgroup.com.au/p/AU-0U68-600V-Aura-Teflon/0.68uF+600V+Aura+Teflon (http://www.soundlabsgroup.com.au/p/AU-0U68-600V-Aura-Teflon/0.68uF+600V+Aura+Teflon)
What the hell...? And if you were J.W. you wouldn't care and select from a hundred the one with the best characteristics, right? The cap itself for sure exceeds the price for a 31bit ADC ADS1281 or ADS1282, so again I wonder if the slope adc principle with all the cirtical parts is reliable enough and if it wouldn't be worth to combine something like STM32 with such a high resolution ADC?
By the way, I was playing around with a TDC eval kit (time to digital converter) a few weeks ago and as long as you are able to give a start and at least on (or two) stop signal this guy is a better choice for whatever into time into digital converter because of its ps-resolution ring oscillator and this for a low cost, space saving one chip solution with the ability for temperature compensation. The maximum samplerate is somewhat like 200kHz under best conditions:*edit: timing related thread derail removed*
And we have learned that it is easier to make (portable) high precision time measurement (thanks to DCF77, GPSDOs or cheap second source RB-references) instead of voltage measurement "without" the reference long-term stability task. Contrary to the mentioned the slope adc still needs the high precision voltage reference.
But I managed to think about the protection stuff. I've updated the repo, so please go for it and have a look at the schematic (pretty basic) and the thoughts gone into it.Cool, I'll have a look at it. Incidentally, you've got a PM.
After that, I think it's finally time for some integrator schematics :)Couldn't agree more. ;D
Audience believe that the new Aura-Teflon is simply the most resolute and transparent capacitor ever engineered, regardless of cost.
And AFAIK for this application teflon is indeed best and most expensive. Then 2nd best is polypropylene and after that polystyrene.
It's not a good way to make an opinion just by the words of a single person, even if it's Bob Pease.
So you better test both types of different manufactors (not with a single example!!!) to find the better one as they will not specify all interesting parameters in their datasheets.
You shouldn't take care of their advertising slogans, but to the electrical parameters.
Concerning soakage you can for sure use one of the shown compensation circuits, but an advantage on compensating one parameter will often have a disadvantage in another, bear that in mind.
Best choice would be an air or vacuum cap but the needed value for the integrating cap is a bit to high. Teflon is expensive and rare this days and my link showed that it seems to be reserved to the audio freaks. You shouldn't take care of their advertising slogans, but to the electrical parameters.
But if there is a possibility to get one of this teflon guys in the bay you should take that chance. You better don't put several caps in parallel as the resulting cap will have a higher leackage.
Concerning soakage you can for sure use one of the shown compensation circuits, but an advantage on compensating one parameter will often have a disadvantage in another, bear that in mind.
We do not have datasheet as such, here is a link to the specs on our
website.
http://www.soundlabsgroup.com.au/c/Capacitors-Teflon/Capacitors+-+Teflon.htm (http://www.soundlabsgroup.com.au/c/Capacitors-Teflon/Capacitors+-+Teflon.htm)
Best wishes,...
We're talking about something in the 220 pF - 10 nF range, depending on what speeds and slew rates and such.
So yes, it might definitely be interesting to see how such a cap would stack up against off-the-shelf parts...
For ease of discussion, lets say a 1 nF cap... How much would one need and where would you easily obtain it? Preferably with non-crazy shipping cost to Europe. Or samples would be great too. ;D
Edit: And to prevent misunderstandings ... this diy teflon cap would be purely to compare it to say a polypropylene, mainly just for the fun of it. It's a hobby after all. :P Not as the primary candidate for this design.
We're talking about something in the 220 pF - 10 nF range, depending on what speeds and slew rates and such.
I ended up with half a square meter for 1nF and thought that can't be right. please check as I am tired and making mistakes now.
We're talking about something in the 220 pF - 10 nF range, depending on what speeds and slew rates and such.
This value seems much to small to me. In this range it should be no problem to get stuff in the bay. I expected a few hundreds nF (Notice to americans: this is a SI conform unit called nano farad, somewhat in the middle of micro and pico farad) up to serveral µF.
Prices are looking reasonable, more later. These materials can be purchased by one individual in some quantity and then after cutting and subdividing with a paper cutter sent to other experimenters using ordinary envelope and mail service for economy.
Suggest to me the best form factor/topology, alternating rectangular plates for a rectangular package or rolled up into a cylinder. I fear rectangular might act like a patch antenna but I know nothing!
Looking at conrad hoffman's page there doesn't appear to be a great advantage to teflon over polyprop in adsorption still it is fun to experiment. I am almost 'having a volt nut' now, just don't want it to happen in my pants ;D
Right now we are looking at a relatively simple version of multi-slope with an ADC in the mix. The ADC is mainly there to drive up the BOM cost and create controversy should anyone check out the repo. ;) It's not as if the idea is to do clever stuff with it and have fun while building this thing or anything. And the aim is to be able to do continuous integration.
For this type of multi-slope 10 nF actually is on the high side. And 220 pF is on the low side, so I would expect we end up somewhere along this range...
Oh and pssst chickenHeadKnob .. *cough* factor of 2.54 *cough* That, and what branadic said.
You're welcome to join the club and help improve the design.Thanks, but I think you've chosen your way, the design is already fixed and there is less place for other/new ideas, that are not common. I'm not familar with FPGA and think this solution is an overkill for me. But I'll give some input from time to time.
however I see a potential improvement; instead of soldering on leads at the end of the sheets/planes wouldn't it be better to solder closer to the center?My gut instinct tells me that the cap will have less performance compared to second-hand market teflon caps, primary concerning long-term stability characteristics as you are not able to incapsulate them well against humidity and with regards to the fact that you will use a copper foil instead of directly plating the teflon foil with the electrodes. Only a few critical points, but I'm sure interested in your test results. Just show me the opposite.
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 ...)
I wonder why there is no project that uses softer goals like 5 1/2 up to 6 1/2 digits, dual-/multichannel input, a seperated board for each channel with some CPLD-based multislope adc or simple 24bit sigma-delta adcCS5532/34 has 23 bit noise free, you could easily do 6 1/2 with that (although INL would corrupt a few LSB). Although I'd try to use the MCP3903, cheaper and a faster SPI, with oversampling and some dither you could probably beat the cirrus.
Personally I don't like 8-segment LED, monochrome LCD or simple dot pixel matrix displays. If you can get a 7" graphic displayI'd kinda like 8 segment LED for the readability ... but you can get a 3.2" touch screen for around 10 bucks, which makes it more attractive.
1) regarding the FPGA: I think a low cost iCE40 with 384 LUTS for < $2.00 (qty 1 from digikey) is good enough to time the discharge on the downslope, from top to zero-crossing. Also, the STM32 counters might be fast enough, but not wide enough and will overflow (do you have timings done yet? How long does a cycle last?). Each iCE40 LUT has 1 LUT, 1 FF, and carry logic, so there is enough there for a few 24 bit counters, and you might even have enough to make a voltage and current ADC if you wanted to. Also see my #6 below regarding the need for voltage and current.
2) the comparator needs to have low offset, and reasonably fast propagation time. Presumably less than 1 clock cycle otherwise you are losing counts. If you are counting at 100Mhz (10ns) you need a comparator that can switch it's output in < 10ns. If it's slower, you get count errors.The comparator doesn't have to be super fast, but it does make life easier. Just as important is that the propagation delay is reasonably constant over temperature etc.
How fast you need to count depends on your desired resolution, the charge up/charge down times, and how many conversions per second you want to achieve.
3) there is an old trick from the Keithley meters to get higher resolutions without necessarily having to go to really high-speed counters (i.e. 100Mhz) and expensive high-speed comparators and precision op-amps..What they do is, for example, count with 10Mhz, then when the zero-crossing occurs, they take that count and save it. Then they amplify the residual on the integrating capacitor x10, reset the counter, and time the discharge of that amplified amount until the zero-crossing again. When it crosses zero, they add that count (divided by 10) to the previous total, then they take the residual of that, once more, x10 again, reset the counter and discharge that to zero. This gives two more digits of precision, using a slower counter, and less precise comparators. And of course it's slower and takes more time. But maybe it's something you want to consider too, to be able to use less expensive parts and still get good precision. If you do this residual discharge with a 100Mhz clock, you might get extra digits into the 7-1/2 to 8-1/2 regions (assuming that the noise, leakage etc, is well controlled).That sounds interesting, how does this amplification of the residual work? Presumably not by increasing the residual charge on the capacitor, so how? Do a S&H, buffer amplify it to x10, and then store that charge on the capacitor, and then do a rundown again? Main part I don't readily see is how to amplify it x10, and then get the equivalent charge on the capacitor again so you can do a rundown again.
4) regarding the input buffer: I think your first choice of LTC6240 is still the best choice. It's < $4 and the chopper stabilized LT1052 is more than $12. Unless I am mistaken, the drift is not important on the input buffer (enlighten me if I am wrong about this). I think the input buffer only has to be stable for 1 conversion cycle. However, for the reference buffer you want to use a chopper stabilized opamp like the LT1052 (maybe not that one for that purpose, just pointing out that the zero-drift is more important on the reference buffer than it is on the input buffer).Agreed. :)
5) for the display, there are plenty of 4.7" and 5" 800x400 LCD with touch displays these days. usually between $20-30. That's not too bad and makes a nice user interface possible.Funky displays is waaaay at the bottom somewhere. ;) And I hope this 800x400 lcd display comes with a decent version of android attached to it, because I for one am not interested in reinventing the gui wheel.
6) finally, I am working on an LCR meter design that uses a 24bit delta sigma ADC ( I am also using the LT6240 as input buffers on that project.. they *are* very nice). You can use the STM32F4 pwm outputs to generate the sine (100Hz, 1kHz, 10Khz, 100Khz, etc), low pass filter it and send it into the device under test. Then measure the voltage across it and current through it and do the calculations. The FPU in the STM32F4 will help here. It's really, really simple to do. I'd be happy to join up on the project and do the LCR part, but the entire AFE has to support 4 wire mode and is basically floating above ground (I measure between RED/BLACK sense leads differentially with two LTC6240s and amplify that with a 3rd difference amplifier, then send it into the ADC). Current through the DUT I measure from the black sense lead through a current sense network returning to analog ground. For a multimeter we'd need to put the voltage divider in front of that. If you want LCR capabilities, you be best to consider it up front.Sounds interesting. :) Do you have a sample schematic of how you think the LCR part should fit into it?
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 (http://www.emsp.tu-berlin.de/fileadmin/fg232/Lehre/MixedSignal/Dateien/Digitalvoltmeter/Schaltplan_DVM.pdf).
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 (http://www.emsp.tu-berlin.de/fileadmin/fg232/Lehre/MixedSignal/Dateien/Digitalvoltmeter/Schaltplan_DVM.pdf).
I've read through the schematic above, banged my head against the wall |O several times, and even did some spice simulations, however, I still don't get how they protect the ADC (or the LTC1150 opamp U100) from input overvoltage when their range switch is on the 2V range and one would feed more than 20V (or: more than 150V, because that's what the U100 opamp can handle at maximum) into it.
Also, the STM32 counters might be fast enough, but not wide enough and will overflow (do you have timings done yet? How long does a cycle last?).You can extend a 16 bit counter + input capture to effectively infinite width in software without much trouble, especially if the period of the signal being captured is guaranteed to be greater than the period of the 16 bit counter. I'm currently using a STM32 at 72MHz to timestamp pulse-per-second from GPS and it's been running glitch-free for quite a while. The algorithm would need adjusting to handle the case where cycles might be shorter but definitely within the realm of feasibility. Being able to just use a microcontroller without any supplemental logic would be quite nice.
Also since this thread seems to mostly be for random people to drop in and barf up some unnecessary bloatware features, allow me to indulge myself: if you're going to have an OCXO anyway, why not GPS-discipline it and have a 10MHz reference output? Haha, I'll see myself out...Or the other way around, which at least for my use makes more sense. Have an external GPSDO with distribution amp and enable the multimeter to use an external 10 MHz reference.
It's a simple design, which as you noticed has no input protection.
*shrug* I found it useful as source of some inspiration.It's a simple design, which as you noticed has no input protection.Yes, but overrange "protection"? So this is clearly a really bad design.
That sounds interesting, how does this amplification of the residual work? Presumably not by increasing the residual charge on the capacitor, so how? Do a S&H, buffer amplify it to x10, and then store that charge on the capacitor, and then do a rundown again? Main part I don't readily see is how to amplify it x10, and then get the equivalent charge on the capacitor again so you can do a rundown again.
Do you have a sample schematic of how you think the LCR part should fit into it?I was going to redraw the front end for this project but I haven't got to that yet... The schematic I do have now is for a client so I can't publish any parts of it. But I'll try to find some time to put something together soon.
You can extend a 16 bit counter + input capture to effectively infinite width in software without much trouble, especially if the period of the signal being captured is guaranteed to be greater than the period of the 16 bit counter.Agreed. I was probably thinking that my software would be busy enough already, but you're right, just adding bits in software is not much of an extra load, so pretty easy to do.
Also since this thread seems to mostly be for random people to drop in and barf up some unnecessary bloatware features, allow me to indulge myself: if you're going to have an OCXO anyway, why not GPS-discipline it and have a 10MHz reference output? Haha, I'll see myself out...... and discipline it with frickin' lasers too ;D
In which case I suspect I already know the approach you mean (multislope). The way you described it sounded a bit ... different. But yes, multislope is indeed the way to go. The current design is a simplified version of multislope (as in multi being two :P), to limit the number of precision resistor ratios to something affordable.
That sounds interesting, how does this amplification of the residual work? Presumably not by increasing the residual charge on the capacitor, so how? Do a S&H, buffer amplify it to x10, and then store that charge on the capacitor, and then do a rundown again? Main part I don't readily see is how to amplify it x10, and then get the equivalent charge on the capacitor again so you can do a rundown again.
I haven't caught up on this thread in a while.. basically, the residual is there already.. it's residual. On the first rundown, when the 0-crossing comparator fires, the micro switches in some analog switches that bring a x10 between the cap and the comparator, then they continue the rundown... when it crosses once more, the micro will switch in another x10 and continue running it down to get the residual until it crosses 0 once more. There is no need to sample and hold, just cross 0 three times, with the last 2 times being amplified crossings.
*shrug* I found it useful as source of some inspiration.
That's true. I tried to figure out how multimeters handle overvoltage/range switching on the ADC; some use zener diodes, but I'm not too confident with those. Also, the Fluke 27 schematic didn't shed any light on that either…The idea is to use clamping diodes so it doesn't go waaay out of range of what the opamp can handle. Then during integration you notice the input is out of range so you switch to a higher range, or open the switch or whatever is the appropriate action. When autoranging voltage I'd say when you detect out of range, you step to highest range, and then step down again to what is appropriate.
When autoranging voltage I'd say when you detect out of range, you step to highest range, and then step down again to what is appropriate.On good meters upranging is faster than downranging, because it can detect without a full ADC cycle. And a good meter must withstand it's rated voltage on the lowest range continuously. Autoranging can be switched off. So I see no point in stepping down from the highest range.
I see the point in stepping down if it's a DIY approach. I was making the statement within the DIY context, not the professional goodies context. Especially when you are not 100% sure yet about getting everything right, then stepping to highest range first and then slowly (while also not being in a hurry) step it down. Because not blowing shit up is more important to me than a few seconds of productivity gain. After you gain more confidence with your DIY solution you can always change the ranging algo, since that part of the software is not all that complicated.When autoranging voltage I'd say when you detect out of range, you step to highest range, and then step down again to what is appropriate.On good meters upranging is faster than downranging, because it can detect without a full ADC cycle. And a good meter must withstand it's rated voltage on the lowest range continuously. Autoranging can be switched off. So I see no point in stepping down from the highest range.
That's correct, however, the input buffer can experience the transients as well (we call that "Impedanzwandler" in german, no idea if there's a direct translation).
Generally with a current limiting input resistor and clamping to the power rails (this can be done with diodes, but BJTs and JFETs are also often "abused" for this because they can have lower leakage, also a JFET mux does it for free).Any specific examples of both parts and exact use of said parts to achieve this?
Look at the service manuals of older bench DMMs, e.g. HP 3456A, Fluke 8840A, Keithley 19x. I attached one example from the 3456A. Just four 27k resistors and two JFET diodes for clamping. These JFET are ultra low leakage, like 2N4117A.Generally with a current limiting input resistor and clamping to the power rails (this can be done with diodes, but BJTs and JFETs are also often "abused" for this because they can have lower leakage, also a JFET mux does it for free).Any specific examples of both parts and exact use of said parts to achieve this?
Generally with a current limiting input resistor and clamping to the power rails (this can be done with diodes, but BJTs and JFETs are also often "abused" for this because they can have lower leakage, also a JFET mux does it for free).Any specific examples of both parts and exact use of said parts to achieve this?
Lol, why didn't I notice this before? Oh wait, you edited. Or I am just blind. No matter... I got the 2N4117A from thisLook at the service manuals of older bench DMMs, e.g. HP 3456A, Fluke 8840A, Keithley 19x. I attached one example from the 3456A. Just four 27k resistors and two JFET diodes for clamping. These JFET are ultra low leakage, like 2N4117A.Generally with a current limiting input resistor and clamping to the power rails (this can be done with diodes, but BJTs and JFETs are also often "abused" for this because they can have lower leakage, also a JFET mux does it for free).Any specific examples of both parts and exact use of said parts to achieve this?
Edit: The relay is just for range switching.
No, that doesn't contain what I was asking about... But in the meantime I did find an answer to the question, which is to use a JFET like the 2N4117A. :) Bit expensive though. :-\I found these threads insightful :
Thanks! Those are indeed quite informative. :DNo, that doesn't contain what I was asking about... But in the meantime I did find an answer to the question, which is to use a JFET like the 2N4117A. :) Bit expensive though. :-\I found these threads insightful :
https://groups.google.com/forum/#!topic/sci.electronics.design/HNi5Bb-rRbE
https://groups.google.com/forum/#!topic/sci.electronics.design/D53KlEoxmD8
If you want to use discretes I'd use one of the low leakage Central Semiconductor diodes (Mouser has them). You won't do significantly better by abusing discrete JFETs or BJTs. As the other thread points out though, some of the integrated MOSFET opamps can do a lot better still.Do you have any specific part numbers of the ones you have in mind here, so I can stare at the datasheet?
All that said, if you want to do auto-zero calibration then you need a mux, even if not muxes are cheaper and more compact than lots of relays ... the mux will probably have protection diodes built in.Same question really, part number to enable datasheet staring? ;D
The thread mentioned the CMPD6001S, but just look up all the central semiconductor diodes on mouser there are a couple with similar specs.Thanks for the confirmation. Search on centralsemi.com turns up basically CMxD6001...
As for muxes, in another thread someone mentioned the MAX4051 since Maxim gives a typical leakage current of 2 fA ... that said, Ti/On semiconductor have versions of the 4051 at a fraction of the cost with a typical 10 fA in the datasheet.
So not the CD4051B (http://www.ti.com/lit/ds/symlink/cd4051b.pdf) then?10 fA typical at room temperature.
10 fA typical at room temperature.10pA not fA.
So not the CD4051B (http://www.ti.com/lit/ds/symlink/cd4051b.pdf) then?What are your requirements? Voltages, resolution, ...?
I wasn't planning on using the CD4051B. I just linked to it to check where Marco got those awesome leakage figures for a 4051 device. But an oopsie of 3 orders of magnitude would explain things.So not the CD4051B (http://www.ti.com/lit/ds/symlink/cd4051b.pdf) then?What are your requirements? Voltages, resolution, ...?
A CD4051 should be fine for a 3-4 digits meter and probably a disaster for a 6.5 digits one.
10pA more like it, but clean the package, clean the board and have soldermask and guard traces and it is likely to go a lot lower. Drop supply voltage to 15V and it will be worse, as this is likely specced at the best conditions.Also pre-assembly cleaning? Or just the whole assembled board? If pre-assembly, any handy tips? Usual procedure would be to put it in an IPA filled ziplock bag in warm water in an ultrasonic bath, but maybe there's better ways?
Finally, the much cheaper jelly bean 2N3904 BJT has a typical reverse leakage of between 30-50 pA, and can go as high as a few hundred pA. These are nice because they are available as MBT3904 in a TSSOP-6 or SC70-6 package for $0.25 so you get two on the same die with similar leakage for $0.12 each.Thanks, that sounds like a good candidate for the protection diodes. :)
The MBT3904 is what I am using for my LCR. I also happen to have many around here so they are readily available to me. Depending on your leakage budget, you can use them as is with an expected leakage max of 200pA (if that works for you) or you can bin them and choose parts with 10-20pA, an order of magnitude smaller.
Icex is a good place to look, as it is a measure of die leakage. You might want to look at higher voltage devices as well if you are going to have a high input voltage, though they will be likely to have worse leakage but still they will be better than a regular signal diode.Thanks. I understand the concept of "is a measure of", but that sometimes is a bit limiting in use... 50 nA max for the 2N3904 ... you state "can go as high as a few hundred pA", so lets say 500 pA. So that's a factor of ~ 100. As a wild guess ... leakage current for the diode connected bjt is very roughly collector cut-off current divided by Hfe?
Oops yeah, dunno what I was thinking there ... still don't see the point in using BJTs or JFETs when the Central Semiconductor diodes are readily available.5nA leakage is a lot. An example, on a 100kOhm protection resistor 5nA causes a voltage drop of 500uV. Not a problem for a 3 digit meter but a bad for a 5 digit one.
Oops yeah, dunno what I was thinking there ... still don't see the point in using BJTs or JFETs when the Central Semiconductor diodes are readily available.Well, one reason might be that Central Semi's marketing monkey needs to have his banana supply revoked. Write a datasheet for a diode marketed as low-leakage, and then you give max leakage only at 25 degrees C. Seriously? Because who needs to know leakage over temperature when they are looking specifically for low leakage, right? Or maybe it just sucks horribly at 40 degrees C. Not saying it's a bad part, but I am saying that whoever wrote that datasheet won't be getting any bonus bananas from me any time soon.
The central semi diode Marco refers to has 500 pA max leakage. At 25 degrees C @_@ So logically 234234000 pAmax at 40 degrees.Oops yeah, dunno what I was thinking there ... still don't see the point in using BJTs or JFETs when the Central Semiconductor diodes are readily available.5nA leakage is a lot. An example, on a 100kOhm protection resistor 5nA causes a voltage drop of 500uV. Not a problem for a 3 digit meter but a bad for a 5 digit one.
John Larkin is a pretty reputable source (moreso than datasheets)But John Larkin isn't downloadable in pdf format from centralsemi.com for easy review.
I got some samples of the Central CMPD6001S dual SOT-23 diodes.
Through a local rep, since their registration/password thing is so
absurd.
I measured about 50 fA leakage at -5 volts. I say "about" because this
is sorta hard to measure... 5 mV across a 100G resistor.
The central semi diode Marco refers to has 500 pA max leakage. At 25 degrees C @_@ So logically 234234000 pAmax at 40 degrees.Oops! I mixed it up with the BAS116.
From the threads I linked earlier :I read that. But hopefully you agree that there is a difference between "an individual on the internet that measured several samples" and "the manufacturer that characterized a large number from different batches". If nothing else, statistical relevance. Not only that, but care to make an estimate of the sampling bias that is encapsulated in the phrase "I got some samples of item XYZ through a local rep"? I know I don't. ;)QuoteI got some samples of the Central CMPD6001S dual SOT-23 diodes.
Through a local rep, since their registration/password thing is so
absurd.
I measured about 50 fA leakage at -5 volts. I say "about" because this
is sorta hard to measure... 5 mV across a 100G resistor.
I hadn't really looked around for specific low leakage diodes before, they've always been too expensive. Ok, so today I looked at the CMPD6001 datasheet. looks ok, MAX 500pA, got it... but.. where's the charts(!) in their whole 2 page datasheet???You are being generous. It's one page packaging info, 1/2 page standard :blah: and 1/2 page with some actual information.
where's the gaussian distribution (histogram) of leakage vs number of units? I want to know statistically what to expect from their part. This saves me having to do binning on another part, for example, if I can predict what the failure rate might be, that rate of failure might be more cost effective than time spent binning, given the part is twice as much money as qty (2) BJTs. If I can statistically trust their part to be better than 10pA 95% of the time, for example, then it's worth it to spend the extra money for these low-leakage diodes, and rework the 5% outliers that fail.Such information would have been nice yes. Given the anecdotal evidence of low leakage (the thread Marco linked to) and the awesomely informative one-liner spec of 500 pA max @ 25 C, the part looks interesting enough that I will try it. But the datasheet doesn't really inspire all that much confidence.
Yes, Mr. Fibble.. that data sheet is a joke.Heh, no kidding. That datasheet deserves an honorable mention here (https://www.eevblog.com/forum/chat/lame-joke-time/msg363992/#msg363992).
PS. this whole discussion is putting the cart before the horse though, you'll not find many muxes or opamps without input protection ... unless you build your own MOSFET input stage or something you'll get clamping diodes as a side effect of your part selection ...What discussion? You mean the side track about diodes? Not as if that was the main track as far as I'm concerned. The horse & cart were already properly located even before the random discussion. But now thanks to the semi-random diode discussion I have a few alternatives for the BAS116 that was already in place. :) Around the opamp that was also already in place. ;)
It's the way of threads like this. People come and go, while leaving some remarks that happen to interest them at the moment.
But now thanks to the semi-random diode discussion I have a few alternatives for the BAS116 that was already in place. :) Around the opamp that was also already in place. ;)
My point was that with the LTC6240 I think you're using and a 100 kOhm input resistor you're already good to 1 kV (10 kV transient) any way without diodes.Speaking of input resistors...
Yellow is fine, is the "dark-colored body or face and a contrasting yellow border, frame, molding, overlay, holster or perimeter." will get you in trouble.
You could do a red face yellow border and you'll be fine. (unless someone else has that trade dress)
OSHW-Multimeter
https://github.com/Stoney49th/OSHW-Multimeter (https://github.com/Stoney49th/OSHW-Multimeter)
While not a true multimeter, I'd always wanted to build my own volt / amp meter with programmable gain and volts / current mode switching.
Without using relays!
Read about it here: http://ludzinc.blogspot.com.au/2014/07/multi-channel-meter.html (http://ludzinc.blogspot.com.au/2014/07/multi-channel-meter.html)
Sometimes the best way to make a complex device is to to one part very well then expand on it. What would be the minimal viable product for an open source meter? Would it be useful to make a device that measures a single thing? Maybe the best place to start is an open source voltmeter. Thoughts?
4. Input Protection
a. Probably just start with Zeners (two 100V “ish” in series) through a high value resistor to ground.
1. Is there any way around having two distinct power supplies (even if batteries) between these two channels? If not (and I suspect this is the case) then at least for a start would 2 AA’s per channel be appropriate as a proof of concept?
2. What’s the best way to handle negative voltage? The ADC’s I’m considering have a range or 0-2.048V with an internal reference. How should I handle this? I’d much rather not have to create a negative supply.
I wrestled with whether or not to start a new thread for this. If anyone figgers it would be better in another forum or thread just let me know.
4. Input Protection
a. Probably just start with Zeners (two 100V “ish” in series) through a high value resistor to ground.
This is similar to how it is normally done but low leakage diodes are used and a high input impedance buffer will be needed.
4. Input Protection
a. Probably just start with Zeners (two 100V “ish” in series) through a high value resistor to ground.
This is similar to how it is normally done but low leakage diodes are used and a high input impedance buffer will be needed.
LM662 will do both those things (not from -20 to +20 V though).
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 (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/ (http://jeelabs.org/) (I'd recommend you take a read of this anyway, it's quite good).
A Keithley 917 for instance has an input voltage range of +/- 200 volts while maintaining an input resistance >200 Tohms.Keithley 917 - what's this?
A Keithley 917 for instance has an input voltage range of +/- 200 volts while maintaining an input resistance >200 Tohms.Keithley 917 - what's this?
Specialized designs can extend it considerably by bootstrapping the input buffer which as a side effect also reduces the common mode error present in a non-inverting buffer.
Specialized designs can extend it considerably by bootstrapping the input buffer which as a side effect also reduces the common mode error present in a non-inverting buffer.
Huh, I never really thought about what would happen to leakage if you connected the input protection diodes to the bootstrapping voltage ... I guess Keithly could get away with two 1n4148s at that point (although they didn't, they used the base emitter junctions of a IT121).
I wish he would comment in the text on why he used the base collector junction in the picture, the text only deals with the use of the base emitter junction.
He mentions the differences between BE and BC junctions when used in this type of application but I do not know why he used the BC junction here either. The breakdown voltage will be higher but that does not matter and it will have slower recovery which seems like it would be a disadvantage.
I couldn't see those pages of the book ... but he does talk a bit more about it in this article EDN was nice enough to dig from their archives :Thanks, that indeed had interesting tidbits in it. :-+ Pity the links to the (presumably) better images are dead, the EDN inlined jpg's were not super duper. But still readable enough. :)
http://www.edn.com/electronics-blogs/designing-ideas/4311721/Bob-Pease-on-bounding-and-clamping-techniques (http://www.edn.com/electronics-blogs/designing-ideas/4311721/Bob-Pease-on-bounding-and-clamping-techniques)
Thanks, that indeed had interesting tidbits in it. :-+ Pity the links to the (presumably) better images are dead, the EDN inlined jpg's were not super duper. But still readable enough. :)
That is common with EDN and related online trade magazines. I expect it more often than not.And the sad part is that the machine on which those jpg's are still exists. They just decided (or probably didn't even decide anything) to not maintain those linked images. From which you can usually extrapolate amusing characteristics about the CMS & backup solutions they use. :P
Their comment system is even less reliable than the EEVBlog forum.
>Quote from: David Hess on Yesterday at 12:58:50 PM (https://www.eevblog.com/forum/index.php?topic=3978.msg531813#msg531813)Their comment system is even less reliable than the EEVBlog forum.
The EEVblog forum is not reliable? :-//
Haven't lost a single attachment or post since it's been running...
Sometime the https://archive.org/web/ (https://archive.org/web/) can help getting old stuff.Agreed. Unfortunately linked images is not the wayback machine's strongest suit. It's rather hit & miss ... mostly miss. Case in point, the hi-res images from that EDN article where not to be found that way.
Their comment system is even less reliable than the EEVBlog forum.
The EEVblog forum is not reliable? :-//
Haven't lost a single attachment or post since it's been running...
Now if someone dropped a bag of transistors in my lap I would have no clue as to how to characterize their leakage. Do you need a pico-Ammeter? or can it be done some sneaky cheap way with a bridge and some op amps?
Simple, just use your 10M input impedance DVM and put the transistor in series with the positive lead, and apply a voltage that is equal to Vceo of the transistor to the whole lot. Then simply bin according to the measured voltage, the lower the voltage the lower the leakage.
(There was always an error when attaching files to the post today, so I put it on my dropbox)Nice, thanks! Definitely better than the low res images. :-+
https://www.dropbox.com/s/nttegd9zwfxh5j3/1983-11-10_pease_clamping_EDN.pdf (https://www.dropbox.com/s/nttegd9zwfxh5j3/1983-11-10_pease_clamping_EDN.pdf?dl=0)
Cheers!
P.S. I'm new here. Does this forum app have a threaded message option?
Hello!
I'm considering building a multimeter as my first serious project.
Something simple at first, as I think it is had a good analog/digital mix. After searching a bit I didn't find many information, do you know about some classes, books, articles that could help me?
Best regards!
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.
I am liking it. Why not kick it up and go for a full android cell phone as a base. This leaves the door open for many bright minds around the world to contribute software with common hardware and operating system. For an example Dr Owen Thomas from the UK , keuwlsoft , would have the software for frequency counter and jitter measurements covered. Someone else contributes software for AC DC Ohms with smart auto select. With a sim card one could make a phone call on their DMM. And lets not forget voice commands " what is the value of this inductance and its Q" , ". "FFT for this wave form please" , " record AC values over 8 hours and email results to myself ". The possibilities are endless once the software is open to science nerds around the world with a common operating system and hardware. The DMM only needs to deal with new standards for sound I.C and high voltage protection. The rest is already in place with a standard android cell phone. I would shell out some bucks if such a DMM came on the market.
http://www.edn.com/electronics-blogs/designing-ideas/4311721/Bob-Pease-on-bounding-and-clamping-techniques (http://www.edn.com/electronics-blogs/designing-ideas/4311721/Bob-Pease-on-bounding-and-clamping-techniques)
Reminds me of the TNG-Tricorder :)I see the similarity. Beam me up Scotty. Did they move actual atoms to do this or just use information and atoms that are already on the Enterprise , somewhat like a 3d printer. From a philosophical point of view it makes a big difference if you are the one that is being transported.
Reminds me of the TNG-Tricorder :)I see the similarity. Beam me up Scotty. Did they move actual atoms to do this or just use information and atoms that are already on the Enterprise , somewhat like a 3d printer. From a philosophical point of view it makes a big difference if you are the one that is being transported.
Old thread!
Sounds like Charles's open multimeter never got off the ground.
Old thread!
Sounds like Charles's open multimeter never got off the ground.
The T400 was such fun to make! I got to learn so many things and acquire new skills. Unfortunately, once the product was complete I found myself with multiple jobs I disliked: marketing, sales, shipping, etc.. It was time to pack up and move back to America to be closer to family.
I'd love to make more lab instruments, but for now I am renovating a house I bought.