For his Hackaday Prize entry, [Martin] is building an Open Source Multimeter that can measure voltage, current, and power. It’s an amazing build, and you too can build one yourself.
The features for this multimeter consist of voltage mode with a range of +/-6V and +/-60V. There’s a current mode, basically the same as voltage, with a range of +/-60 mA and +/-500mA. Unlike our bright yellow Fluke, there’s also a power mode that measures voltage and current at the same time, with all four combinations of ranges available. There’s a continuity test that sounds a buzzer when the resistance is below 50 Ω, and a component test mode that measures resistors, caps, and diodes. There’s a fully isolated USB interface capable of receiving commands and transmitting data, a real-time clock, and in the future there might be frequency measurement.
This build is based on the STM32F103 microcontroller, uses an old Nokia phone screen, and unlike so many other multimeters, this thing is small. It’s very small. More than small enough to fit in your pocket and forget about it, unlike nearly every other multimeter available. There’s one thing about multimeters, and it’s that the best multimeter is the one that you have in your hands when you need it, and this one certainly fits the bill.
The entire project is being written up on hackaday.io, there’s a GitHub repo for all the hardware and software, and there’s also a video demo covering all the features (available below). This is a stand-out project, and something we desperately want to get our hands on.
Very impressive hoping kits are coming to Tindie.
Damn neat small package, even if the accuracy is pretty terrible its going to be useful, and the tests shown in the project log show it to be reasonably good.
Assuming it’s as functionally sound as it seems from a glance I feel like I need a dozen.. (One for every room I end up doing projects in (when the workshop is in metal/woodwork mode any flat surface might become the electronic test bench) and a few in the workshop for those bigger projects..)
Be interesting to really map the accuracy in all modes against a fancy model in all climates etc.
Looking forward to the software updates mentioned.
“from a glance I feel like I need a dozen”
I already have more than a dozen of the Horror Fright “free” DVMs!
B^)
Me too, and I’ve only had one crap out in a number of years. Well, except for the leads, which break a lot and may not be up to Fluke quality, ahem. Yesterday I was measuring 400VDC, and a fleeting thought went through my mind that I was taking my life in my hands, literally. But those cheap meters seem to be quite accurate.
People go ga ga over OS. The specs are awful. The wattage is interesting but when I wanna see that I am usually interested in AC and I can plug in my KIll A Watt or get my clamp on meter that measures watts if I put the probes on to measure voltage (as an aside, it would be nice to be able to tell it to just assume 120 or 220 and know it is not a “dead nuts” reading, but I digress). No AC range, silly DC ranges,.. I will stick to my free ones from HF and my ring light if I need continuity. Outside of it being open source it seems pretty crippled spec wise.
I would love to see a 4-20mA output built into this for generation the loop for the testing of various PLC’s.
Would be nice for actuating an electropneumatic valve too
the EspoTek Labrador is also opensouce and a logic analyser, a signal generator, and an ossiloscope..
I wonder how it handles reverse voltage/current without subjecting the gpio to reverse voltage?
Is it difficult to do auto ranging for the 2 ranges?
Third line, it’s bipolar. Good to go for us all.
I found out how: it uses an analog front end that biases up 1.25 volts, then uses a resistor divider to scale down. Voltages are sampled at both probes (iirc) and subtracted in the stm.
Hmm, definitely worth a look also as training aid for new naive technicians we have so much fun with ;-)
Thanks for posting.
I wouldn’t trust this one more than anything say 48V or less. where is the Class III/IV isolation/insulation?
Great for a hobby project, but if you are working with AC, or anything above a few mA, you are playing russian roulette, and loading more than one projectile.
” What it does not do:
it does not measure mains, nor is it meant to; I rarely use mains, so I don’t need this function, and because of safety I did not even try to implement it “
If you DO need mains level measurements there is always the EEVbog meter. Its better than anything fluke makes for the same price and it is designed by/for sane people rather than by marketing departments and for managers with budgets to use up.
Great hobby project, but like many other here I would not trust this with anything that could go “boom”. No more than 12W, 48V *or* 1A.
Also not to burst anybody’s bubble, but there’s already an opensource DMM that you can buy https://www.eevblog.com/product/121gw/ And when that crazy aussie bloke says “600V CAT-III” you better believe it! If watching Dave over the past 10 years has taught me anything it’s that he’s religious about DMM design and specs.
I think this is a great project. The meter does what he needs it to do – with appropriate disclaimers as to it’s capabilities – and he’s shared all of the design info and code. You could certainly add input protection if necessary, and it’s something you can actually build yourself rather than spending 20x more on a fantastic but not really open source 121gw (afaik, UEI has not released the firmware source)
Congratulation, nice job!!!
For those interested in similar projects, have a look at our Pocket Science Lab: https:///pslab.io It’s a pcb interfacing to a mobile as the UI. Everything open source of course. Functionality includes multimeter, oscilloscope, logic analyser, wave generator and many more… The pcb´s are available for order, worldwide.
We are currently also working on an open hardware version, stay tuned…