Count me in! I have some experience with very low voltage precision measuring (http://www.mastrogippo.it/eeg/) and I'm pretty good at firmware if we use PICs. But I think a ti MSP430 will fit better. Good way to learn!
im thinking, maybe "dual display" ? Some nice LED 7-segment for "main" display and 4x20 (or graphic) LCD for other things like menus and other measures.
So for example u can have Vrms on nice big LEDs + other measures like Vp-p, Min-Max, or freq on LCD. Or even dual-measure, for example I on LED and V on LCD + power and resistance calculated from it :D
Cool idea.
I think it's gotta be different somehow, not just a bench multimeter.
I'm not sure what or how, just offer something compelling, either in form factor and/or combination of features.
Be careful not to slide down the oscilloscope functionality slippery slope...
Dave.
A micro SD slot is tempting too.
I think hacking a Fluke is a bit blaspheme ;D , but maybe if we can find a good multimeter with a nice analog front-end to harvest for cheap, it would save a ton of time.
I always wanted to build one of these:
http://mondo-technology.com/super.html
we can get a lot inspiration from that project! ;)
What I would like to see, is some modern computer interface, USB or even better for long distance logging, ethernet. Of course, the isolation/safety issues will arise then.
Actually, what I like about mains powered meters is that I have never had to run around finding fresh batteries before starting measuring with them ;) Unlike my Fluke 89IV, which seems to eat AA's like bread. That is why I like the Agilent 34401A (or any similar) so much.
Regards,
Janne
I definitely do not want to make this a scope lol (Rigol and others have nice cheap units ;))
I am thinking one idea to set it apart is to make the current input separate, so we can compute Power :) Also so we can display current and voltage at the sametime, compute power factor and VA for AC, Power for DC.
I would like to slip in a small PSU, if only to charge the battery. I have built in 1.2Ah 12V gel cells in equipment (they only way a couple of hundred grams ;).
USB PC Connection is a MUST.
I love Dave's idea about about having a simple serial terminal. That would be a Awesome feature. If we are gonna go that route might as well add I2C and SPI Analyzers Etc...
My opinion about the Ethernet is that it kinda adds a huge amount of complexity / expensive parts for a feature that I don't know how useful it would be to most people. But like was said before we could always go for a modular type of a system where that could be a addon feature or something.
Usb and ethernet cables on a multimeter are just a disaster waiting to happen. It's not a good idea to connect a multimeter to the common ground, because if you don't isolate everything you will end up shorting things to ground if you measure a signal with a floating reference. I think wireless (bluetooth, zigbee, custom 2.4ghz) is a better option.
I don't see any benefit in using an ARM, I think all the tasks we need can be easily handled by an easier micro.
I suggested the microSD because they're, well, micro, but a regular slot will be ok too because you can find adapters everywhere.
Sorry Dave, but I think that a rechargeable battery is a must if we want an OLED diaplay, wireless, SD slot.... But I wouldn't go the SLA route, li-ion are cheap and easy to work with, SLA weigh a lot and has Peukert and is big...
We should try to focus on building a meter, and keeping it simple and useful (and CHEAP!!); I understand the enthusiasm, but adding tons of features that don't belong to a meter will only be frustrating in the end imho. :)
*Serial IR ; slower speed, but the SD-Card could be used as a buffer.
*An SD-Card or usb flash drive is a must for data logging. (for high speed data logging maybe 1~2Gb RAM)
*Auto Ranging?
*3~5 channel Volt meter/logic And Dual channel Amp meter.
*Would like the ability for 10~20 DC amps continuous.
*Ability to measure Resistance, Diodes, Inductors, and Capacitors.
*maybe a Transistor tester.
*micro volts/amps or pico volts/amps
*maximum 600 Volts to 1Kv ?
*phase angle (for three phase power) ?
*able to use Fluke Clamp-on Current Probes (for three phase power) ?
*low frequency Oscope ability (less then 200Khz) ?
*A Wall-adapter for a PSU.
*Able to use a Lithium-Ion battery pack from a cordless tool (non-charging). If your some where and the battery dies then you could use the one from a power tool.
*D cells or the Big 6volt battery, both are easy to find.
*In Resistance mode it could tell you the color code and if it is within tolerance.
*Maybe a Composite video output.
Well, if u have ethernet u can connect it to pretty much everything everywhere :)
Another idea:
Maybe split it into 2 parts, analog input + simple uC to interact with A/D Conv. + "head" with screen and all other measurement functions connected by infrared or optocoupler. So when something fails on analog part, digital part with SD/USB/Ethernet and other fancy stuff is safe. Would be easier than isolating USB
Well, if u have ethernet u can connect it to pretty much everything everywhere :)
Another idea:
Maybe split it into 2 parts, analog input + simple uC to interact with A/D Conv. + "head" with screen and all other measurement functions connected by infrared or optocoupler. So when something fails on analog part, digital part with SD/USB/Ethernet and other fancy stuff is safe. Would be easier than isolating USB
Agilent power supplies controllable via GPIB or Ethernet are done just this way. Probably their bench DMMs too. One should be very careful about the isolation. Handheld DMM is especially critical since it is "hand held". Bench thing is somewhat easier in that sense.
Ethernet line transformers are tested 1 kV RMS isolation, but that is not enough for safety. Something like 5000 V RMS would be more appropriate there. But anyway without extensive testing, there is no way to guarantee safety (or any CAT-rating), as Mr. Maxwell tends to be more imaginative than we poor design engineers ;)
Add capacitor ESR measurement to the functionality list. This should work downto 1 milliohm (4-wire measurement required?), since most ordinary electrolytics are rated something like 10-20 milliohms.
Regards,
Janne
Yes, ESR and Dave's uCurrent are a must! ;)
I'm a bit scared of ARMs, that's why I was supporting PICs.. But if someone manages to get an easy bootloader working, I can try to join the fun! I've been thinking about learning ARMs for a while... Maybe we can start on the mBed platform, http://mbed.org/! All the hard part is already done.
I'll watch this thread with interest. After all the ideas have been thrashed around, someone (GeekGirl) is going to have to take control of the situation and decide on a specification for the design. Then organise people to contribute to it. Without the spec or the organising, nothing will get off the ground so I think it's pretty important.
Brian
I should get one of those though, I think.
I'll watch this thread with interest. After all the ideas have been thrashed around, someone (GeekGirl) is going to have to take control of the situation and decide on a specification for the design. Then organise people to contribute to it. Without the spec or the organising, nothing will get off the ground so I think it's pretty important.
When it comes to the enclosure I am going to suggest that we use Farnell / Newark, this is so that we can all have everything FIT, Front Panel overlays the right size etc.
http://www.polycase.com/item/vm-36boot.html
this looks nice and cheap. I would like a handheld multimeter, not a bench one...
When it comes to the enclosure I am going to suggest that we use Farnell / Newark, this is so that we can all have everything FIT, Front Panel overlays the right size etc.
When doing a project like this I like to start with the form factor and user interface first and how that's all going to work, and then work backwards to the detailed schematic. Because a schematic does not a project make.
http://www.hammondmfg.com/
http://www.serpac.com/
http://www.polycase.com/
are some of my favorites.
Also, I'd consider a budget too, too high a price and it's going to be a show-stopper, so cost should always be factored in.
I'd probably go with PIC myself for familiarity and simplicity. 32bit ARM power is not needed for such a thing, and the development tools are harder to work with for the average punter.
It's hard to beat the $40 PICkit, MPLAB, and free (limited) C compilers for the PIC combo.
A lot of people say ARM and GNU C is cheap and free, but when it comes down to it the tools are not consistent, and harder for a beginner to use.
But of course that may not really matter if most people just want the finished pre-programmed product.
Heck, I'd even seriously consider jumping on the Arduino bandwagon here. Separating the custom front end board from the processor board entirely. Gives options and lowers the development risk. And it will excite the hacker and makers (don't underestimate that market appeal)
Dave.
I think the bench-top would be most appropriate and easy to build. But hey, it's going to be open-source, so anyone can build their own version, if they like!http://www.polycase.com/item/vm-36boot.html
this looks nice and cheap. I would like a handheld multimeter, not a bench one...
Nope, Can not use them.... They don't come in PURPLE ;);)
I think if we can make it modular then we can have a simple front end display for hand held and a fully optioned desktop model ?
The prices of the hand held case is VERY GOOD, for low qty.
I think that we need to cull the list and not make this project a tool for every situation.
I am not sure, but I am sure that in the next few days I will make a list and description of every idea so we can work out what we REALLY want in this product.
http://www.polycase.com/item/vm-36boot.html
this looks nice and cheap. I would like a handheld multimeter, not a bench one...
With regard to compilers, if it is decided that the PIC route is the way to go, then I would recommend the BOOST C compiler. It's not the *best* compiler in my opinion (that award goes to Hi-tech PICC), but it's certainly the best bang for buck. Even the professional version is well within most people's budgets. I used to use Hi-Tech but found that it was priced outside of my range for my hobbyist stuff. So I've recently moved to BoostC.
If someone does not have a PICkit to program the microcontrollers, They could just order the PIC with the code already programmed into it. I have a pickit2 so its not a problem for me.
"Looking for a low-cost programming solution? Let Microchip do the programming in a fast, cost-effective, secure and proven method."
But I wouldn't try and make it all the one unit, I'd have them as separate modules. One as the bench meter/data logger/oscilloscope, one as the bench power supply (that could also power the other modules), one as a PC/Ethernet/WiFi comms module etc.
I think at first we should make the internals only, and let people decide what kind of enclosure they want. Then as we get going maybe someone will find a standard case that we can all use.
This usually doesn't work out. Too many parameters depend on the enclosure. In my experience, if you go with an off-the-shelf enclosure, and if you don't want to go through many design iterations, you have to take care of the enclosure early in the project, not late. Otherwise you end up with the typical DIY enclosure: A huge, half empty box, taking up much more bench space than necessary, with PCB(s) somehow mounted on glued standoffs or other makeshift mechanical support.
One of my first posting in this thread pointed to such a DIY system. You can get some inspiration by looking at the pictures in
http://www.heise.de/ct/projekte/machmit/ctlab/wiki/LayoutSeite
http://www.heise.de/ct/projekte/machmit/ctlab/wiki
http://www.heise.de/ct/projekte/machmit/ctlab/wiki/AlleModule
And also, who is the target audience?
Just GeekGirl to fulfill her fantasies?
(;->), professionals?, hobbyists?, education?, Hackers/Makers?
etc.
Sure, projects can be done "just for the heck of it", but it's nicer if you can target an intended niche.
Dave.
I suggest a vibration function in the continuity mode, so we can really fulfill GeekGirl's fantasies! ;D (Sorry, couldn't resist.)
I definitely agree that this should be a Bench Meter and not handheld....Yap, I agree.
I think that we should try to do some type of modular design....
I dont know if we wanna go the Arduino route, those things are so expensive for what you get. Since we will most definitely be making PCBs for modular boards and things like that, making a Main board with a ~$5 PIC Chip seems like a better option to me then having to make the Main board and the have a 30 dollar Arduino attached to it anyway. Unless you are saying that we should just use a Arduino compatible chip on our board and use the Arduino bootloader and IDE to write our code. .....
If you went PIC then you'd need a good reason the stray from the free Microchip C compiler.
If you went PIC then you'd need a good reason the stray from the free Microchip C compiler.
I must confess I've never actually tried Microchip's own compiler. The simple reason being, they don't support (or at least they didn't) the 16F range of devices. While I was learning C, these were the devices I was playing with, so I had to find a compiler that worked with them. That's how I got on to PICC.
Once you're used to a compiler, you don't really want to have to swap to a different one (at least, not just for the sake of it anyway). Hence I never got around to trying Microchip's own compiler.
Brian
Unless you are saying that we should just use a Arduino compatible chip on our board and use the Arduino bootloader and IDE to write our code.
Unless you are saying that we should just use a Arduino compatible chip on our board and use the Arduino bootloader and IDE to write our code.
Yup, that would be the best option I think. It fulfills GeekGirl's AVR fetish, keeps the cost low, and it gives the hackers free easy to use tools, gives it the requisite "community" feel, and no programmer required, just plug into USB for programming. Internal ISP header on board for initial bootloader programming of course.
I see few downsides there.
Dave.
I don't see the benefit of plugging in USB rather than plugging in a ISP connector for programming...?
There's a lot of overhead when using Arduino language, http://hackaday.com/2010/01/06/arduino-io-speed-breakdown/. The only way around this is to bypass the Arduino abstraction, in which case you might as well not use it anyways and just use gcc compiler.
I don't see the benefit of plugging in USB rather than plugging in a ISP connector for programming...?
There's a lot of overhead when using Arduino language, http://hackaday.com/2010/01/06/arduino-io-speed-breakdown/. The only way around this is to bypass the Arduino abstraction, in which case you might as well not use it anyways and just use gcc compiler.
Aaand You don't have to use it, you can just use plain GCC so it's best of both worldsThere's a lot of overhead when using Arduino language, http://hackaday.com/2010/01/06/arduino-io-speed-breakdown/. The only way around this is to bypass the Arduino abstraction, in which case you might as well not use it anyways and just use gcc compiler.
I don't see speed being an issue in this app. But the benefits of using Arduino are potentially quite large.
Dave.
....
My original idea was to build a "Bench Meter" with good specs (higher than my Fluke 29).
Now people are indicating that they would like an entire DIY lab.... I have no problem with this. I personally think that if we design an open protocol for comms, we can hang anything off it :)
....
...
Dave, can you take some pictures of the analog frontend boards of your most expensive multimeters? Only board layout can be copyrighted, schematics can't, so if we can get a ready to go schematics we can design a slightly different board and have a product as good as the cool guys, for the price of bare components.
...
In the interest of moving things along -- while I'm sure everyone has their own opinion on what their favorite case/microcontroller -- I think most people here would agree that it's more productive to choose *something* even if its not their first choice, rather than sitting around arguing.
So I propose a vote (choose only one option):
1.) PIC
2.) AVR/Arduino
3.) ARM
For the case, I haven't seen many objection to the case proposed by Dave, http://www.polycase.com/category/zn-series.html (http://www.polycase.com/category/zn-series.html). I definitely think that a benchtop case is a good idea for a do-it-yourself kind of a project, even though handheld might be more convenient with a production unit.
What about ignoring processor and just making SPI or I2C modules that make up various instruments. There are various items that most instruments need and people could stitch them together whatever way they need.
For example a DC volt meter would need a relatively noise free A/D. It would also need a precision reference, a switch MUX of some kind, a PGA, a voltage divider network, an analog power supply and a digital power supply. Most of these are basic items that any instrument could need.
If you were making an AC volt meter you would also need a True RMS converter or precision bridge. Virtual instruments made up of these sorts of components would be an interesting way to take things. Volt meters, power meters, LCR, etc could all be built from various components. People could add various modules to their box depending on what they want to do. Not everyone needs 6.5 digits of accuracy, so they could get a cheaper A/D unit and a noisier PGA. Since everything is a virtual instrument various items can just be plugged into a switch matrix.
Could be a bit large of a project though.
We could discuss that for ages, it's the old Atmel,Microchip,Younameit discussion...lol, yep we could. So far AVR is winning in the poll for this.
The main argument I see for using a 32-bit micro (ARM) is a graphical LCD (or OLED ;)). This might be nice for large numbers (your standard character LCD is a bit small for bench DMM IMO, and 7-segment is less flexible), dual display (like the Fluke 45 (http://us.fluke.com/usen/Products/Fluke+45.htm?catalog_name=FlukeUnitedStates)) or graphs (both bar graph and histogram). I believe 8-bit micro's are a bit short on memory for this task (unless you go for the largest parts that costs more than a basic ARM). I don't have experience with ARM though, I've only used AVR.For me main argument in favour of ARM is not graphical LCD but fact that those micros have much more things inside, like AT91SAM7X256 with Ethernet, USB and several serial interfaces and it doesn't cost much more than similar AVR ( 10$ vs. 6$ for atmega128)
Apart from this, an 8-bit micro should be plenty. The fastest most commercial units can sample is 2kS/s (Agilent 34401A, Keithley 2000, the most recent modules might be faster), and this is obviously at reduced resolution. A 20MHz 8-bit micro should be able to handle this unless you do tons of floating point math. I think sampling this fast is only useful in assembly line testing anyway, where you want to test a continuous stream of products. It's nice if you have a bar graph that's reasonably fast (most Flukes do 50S/s AFAIK). We will need a fair amount of I/O's though (display, buttons, ADC, relays for things like range selection, serial/USB/ethernet out).
As I said, I think our major concern should be designing a usable ADC!
The userinterface and interfacing with other stuff is not really complicated.
I don't have much time on my hands now but I will look into reverse-engineering and drawing schematics for something that is based on the Keithley 196. This should provide a good basis from which we can work on...
And I agree, only fancy graphical interfaces would require a bigger ammount of computation time, but people get along with just 8-seg displays ;)
The main argument I see for using a 32-bit micro (ARM) is a graphical LCD (or OLED ;)). This might be nice for large numbers (your standard character LCD is a bit small for bench DMM IMO, and 7-segment is less flexible), dual display (like the Fluke 45 (http://us.fluke.com/usen/Products/Fluke+45.htm?catalog_name=FlukeUnitedStates)) or graphs (both bar graph and histogram). I believe 8-bit micro's are a bit short on memory for this task (unless you go for the largest parts that costs more than a basic ARM).
*aehm*.. http://rossum.posterous.com/teeny-avr-media-thing-the-nanotouch-0Yeah, as long as you can avoid using a frame buffer it can work.
;D
If I want 32 Bit, I would go to the AVR32 line before ARM, but that is only due to the fact I have no experience with ARM :( although I am prepared to jump in an learn ;)Well both are supported by GCC so probably biggest difference would be how to configure things like SPI/UART etc., probably some code can be even ported from avr ^^
After reading a bit, I think that we might get around using this (http://datasheets.maxim-ic.com/en/ds/ICL7109.pdf) chip for a start, it should provide satisfactory accuracy.From a quick glance at the datasheet, this device doesn't seem much better than the ICL7106 used by all cheap multimeters, just 2000 counts (decimal).
I'm still reading into integrating ADCs, but it seems that getting reliable results will require quite some effort. I will start experimenting as soon as I get the FPGA project for school done... :)Building a high-accuracy ADC is probably quite hard. If we have to use an off-the-shelf ADC, there are plenty available with a higher resolution. A quick parametric search at Digikey shows several 24-bit ADC's below $10 (eg. AD7192), although getting 24 bits of usable data out of them won't be easy either. Not sure what the important specs in this application are, it may well be that what required a custom circuit in the eighties can be easily solved with modern parts.
When it comes to the enclosure I am going to suggest that we use Farnell / Newark, this is so that we can all have everything FIT, Front Panel overlays the right size etc.
When doing a project like this I like to start with the form factor and user interface first and how that's all going to work, and then work backwards to the detailed schematic. Because a schematic does not a project make.
http://www.hammondmfg.com/ (http://www.hammondmfg.com/)
http://www.serpac.com/ (http://www.serpac.com/)
http://www.polycase.com/ (http://www.polycase.com/)
are some of my favorites.
Also, I'd consider a budget too, too high a price and it's going to be a show-stopper, so cost should always be factored in.
Is this project dead?It was dead right from the beginning. Because
It might not be worth the effort to build a high accuracy meter or an extra cheap meter, but there are some niche applications where it makes sense.So, you are volunteering to fix issues a) to f) above, or ...
Such as a meter that automatically calculates average and peak power. Or a datalogger that records voltages to a SD card at a sample rate of a few Hz or kHz.... do you just want to add to the wish list?
In any case, we'll make the assumption that the accuracy needed is comparable to or less than that of the under $20 meters and that the builder already owns a meter (and calibration reference) much more accurate than the one being built.That excludes all those who were after a high-precision meter for next to nothing.
One extremely high accuracy measurement that is relatively easy to make is time/frequency. Put a GPS in your homemade frequency counter and you'll very likely have more accuracy than you'll ever need.1) What has that got to do with a bench multimeter?
I imagine that conceptually it is a pretty straightforward idea.Then do it. Don't talk, do it.
I imagine that conceptually it is a pretty straightforward idea.Then do it. Don't talk, do it.
Could you be a little bit more helpful?
I'm interested in learning as much as I can. This forum is a treasure trove of knowledge. That's why I asked. My education certainly isn't your responsibility, but any help you would like to offer would be appreciated.You just got an education. Don't talk, do, especially if you think
it is a pretty straightforward idea.
Why? I owe you nothing.
You just got an education. Don't talk, do
And automatic calculation of averages and peak power can be done with any piece of rubbish that has a PC interface, plus some PC software. I never checked what the cheapest meter with a PC interface costs. I know a VA-18B can be had for 40 € (new).That's true of steady DC, but not for AC or DC with significant AC ripple. For AC, you'll need to sample both the voltage and the current, then multiply them together and take the average. A normal multimeter would also sample too slowly to catch a brief inrush. (And if your supply voltage changes over the course of the measurements, you'll need a second meter to be able to read both voltage and current. It still won't work for AC measurements since you need instantaneous voltages and currents, not RMS.)
I'm sort of interested in the idea of this, so, realistically, what is required to make a meter? I imagine that conceptually it is a pretty straightforward idea. A voltage reference and an ADC. Compare the incoming voltage with the reference. Use a DSP to analyze the input and do whatever you want with it, whether that's measuring the average of the input, p-p voltage, Fourier analysis, etc. Feed it to an mcu/mpu and display it on a nice little screen. Of course that's just voltage. I would think current could be measured in a similar manner. Really, as far as quality goes, what would be required to make it as high-quality as possible? I would think basically just an extremely accurate and precise voltage reference, high-quality ADC, and measures to minimize input noise. Is there anything (probably a lot) that I'm missing? Because it really sounds fairly simple to me. Simple idea, hard to pull off, I would imagine.
I think we should discuss on getting those figures and schematic(!) idea's on table first, before adding anything else to the discussion on the 'digital section'. In my opinion a high-count multimeter is more about the analog circuitry, because that needs to be done well. A digital circuit is more like connecting the pins correctly when the right parts are chosen for the job.