STM32 Open Source Multimeter
embedblog.eu
embedblog.eu
This meter is nice, but the relay on the current range select (K2) is set up so that there will be a break in the current when it switches ranges. On inductive loads, this would cause arcing and can damage the relay. It could also shoot through D6 into the voltage rail, potentially frying the meter. On digital loads, this blip in power might be enough to reset the circuit you're trying to measure. A better way to put the relay is to always have the 10 ohm resistor in series, and switch in the 1 ohm in parallel when needed. Of course the resistance will now be 0.909 ohms instead instead of 1, but that can be calibrated for in software.
The tricky part of a multimeter is not the digital part (which is a knob in many multimeters) but the analog part: calibration, stability, noise. (And, as martin points out, safety.) The three-to-five-digit output here suggests an accuracy of ±0.05% or better, which is not easy to achieve, and it turns out at the end that the accuracy is about ±5%. (Expensive multimeters can deliver 7 digits, and for real.) In theory the STM32's ADC can deliver ±0.1% error easily, and its internal bandgap reference ±2% (accuracy, not reproducibility), so it ought to be possible to do better. But I happily used analog multimeters with several percent error for many years. In fact, I still do sometimes!
If you like this multimeter, you'll probably like the M328 "DIY hobby Arduino voltmeter" or "AVR component tester", which you can buy prebuilt from a variety of places. It does component identification — it's a full RLC meter, with automatically triggered transistor and diode test modes — but is unfortunately built around the AVR, limiting it quite a bit. And it usually (always?) has pretty poor precision.
Is there an alternative repository to Thingiverse yet? They're run by notorious bad actor MakerBot, so depending on them to archive our manufacturing knowledge hardly seems prudent.
I've bought a DSO138 DIY Oscilloscope Kit clone in eBay and I'm scared to connect it to 220V main line because I've not reliable information or safety warranties (It's a clone, not the DYE Tech certified one).
Not everybody cares about safety as they should.
Che, no te importa si cuelgo de tu wifi, o sí?
Oiga! Yo le subo wifi, usted baje unas chelas fresquitas! :p
If you're talking about the power adapter, you can buy a reputable one (it's external to the scope).
If you're talking about measurements on 220V equipment, just buy a genuine Digilent (or other brand) probe with 10x attenuation for about $20, then you can have complete faith in that the scope electronics will only see signals < 48V, which is completely safe.
You talk like you trust quite much in Digilent. I'll keep it in mind when looking for some instrumentation. Thanks a lot!
After it is well tested (measuring temperatures is hard, but doable) and you are confident it works, you can use it normally.
Anyway, I really encourage you to doing DIY projects at home. Most of them work in low voltages between 5 and 3.3V, risks are close to nothing.
This is something very close to my heart that I’ve been wanting for a long while now. Thingiverse is not only run by someone I don’t wish to support, but is also a measurably crap site. It’s slow, search barely works, etc etc. Bring up the name to anyone and you’ll instantly hear endless complaints.
But.. there’s nothing better.
The new Prusa site is Gcode only, and very limited in features. Grabcad is a mess of annoying UI and endless low quality models, but kinda works.
We seriously need a Github for 3D designs and electronics. Allow sharing of any filetypes, from STL and OBJ to raw CAD files, as well as wiring diagrams and PCB schematics, richtext assembly descriptions (like Githubs readme files), and a way to preview the model files visually like Thingiverse/Grabcad.
There’s huge demand for a service like this and there’s income to be made by allowing people to get parts printed or PCBs manufactured via referral to appropriate services.
https://www.thingiverse.com/thing:3660755
Open Source STM32 Multimeter case by embedblog is licensed under the Creative Commons - Attribution - Non-Commercial - Share Alike license.
What does this mean?
Remixing or Changing this Thing is allowed.
Commercial use is not allowed.I am a staunch fan of GPL. If you want to reproduce my physical stuffs I've released, be my guest.
If you make changes, you had better make them available in accordance to the GPL. I'd like a PR on my repo, but that's a niceity- not a GPL requirement.
Some of my GPL3'd hardware:
RadioInstigator: https://hackaday.com/2019/06/05/mobile-sigint-hacking-on-a-c...
Repo: https://gitlab.com/crankylinuxuser/siginttablet
Closed Loop Controller for 3d printers (steppers): https://gitlab.com/crankylinuxuser/closed_loop_system
Personally, I will only run gcode I've generated myself on my machine, but it's a fair experiment to run. I haven't run across any postings on prusaprinters that don't provide a proper STL or OBJ.
The 2nd item there was generally the main one. eg Going back on the Open Source nature of their work, patenting progressive ideas contributed by their Community members, etc.
We’ve talked about it plenty at Hackerspaces I’ve been part of, and there’s various attempts at it but none seem to hit the spot the creators are after.
https://hackaday.io is probably the closest but the UI is a mess, there’s no previewing of the files, etc.
I’m literally picturing something like Github with file previewing and some other features added. Love the idea of having issue/bug reports, file versioning for iterations, forking, etc etc.
Of course you’d get content thieves posting stuff that’s not theirs, but you get that on all sites with UGC and it could be moderated/reported.
So most Thingiverse designs that are copies of existing products are probably entirely legal, or legal except in a very few countries where they infringe Saudi laws about nudity depictions or patents or something, but by the same token, in many cases the licenses of the Thingiverse Things will not be usefully enforceable, because the STL (or perhaps a resampled version thereof) is statutorily not subject to copyright.
I've been developing a GitHub/GitLab/Gitea style website for a while now, for storing and displaying binary objects. The current code is set up to handle SQLite, but it's entirely feasible to add support for other binary formats (such as 3D objects) to it:
eg storage of them, display of them visually instead of the SQLite table view
When I was first thinking up the idea... it was actually for 3D objects. Was going to do it as a Collab platform for Blender, but well... I do more stuff with databases so the SQLite bit came first. :)
The backend storage doesn't use git, as it's lousy with larger files over time, but it does use the same principles for the versioning, branching, forking, tagging, etc.
https://github.com/sqlitebrowser/dbhub.io
Don't be faked out by what looks like no activity there since May. I'm working heavily on fixing some stuff in the Go WebAssembly ecosystem, so a decent data visualisation layer can be added to the current site. ;)
For what's worth, GitHub actually renders STL as a 3D representation, if you click on the file, e.g. here [1]. (Just a random example, I'm in no way affialiated with the project).
Of course, it's still lacking important features, e.g. search parameters, etc, but... it could work.
[1] https://github.com/iliterobotics/3D/blob/master/Justin/Uncom...
Considering hardware projects are just software (CAD files, schematics, diagrams, documentation) I’d love to see Github or Gitlab or someone take this on.
Back in the way back times Steve Ciarcia wrote an article on doing this with a BASIC program talking to a board with a DMM chip called "Try an 8 channel DVM Cocktail." It used the MC14433 which Microchip manufactured as the TC14433 (http://ww1.microchip.com/downloads/en/devicedoc/21394d.pdf)
[1] 3 3/4 digit -- https://www.digikey.com/product-detail/en/maxim-integrated/M...
[2] 4 1/2 digit -- http://ww1.microchip.com/downloads/en/DeviceDoc/21459E.pdf
FWIW I ordered one to see if I can get it working on one of my many ST Micro Nucleo boards.
Pretty sure it's chapter 5.
- looks like crap
- missing a ton of regular expected features
- has a couple features that you'll find nowhere else
- you'll spend more time getting it working than using it
But damn is it awesome.
The STM32 part used in this project has two ADCs that can be triggered simultaneously, so you can actually do two readings at once.
Placing fuses on voltage and resistance inputs does not make much sense as the input impedance should be high enough that any sane voltage will not cause any damage (MCP6072's datsheet does not explicitly state the safe maximum current through internal clamping diodes, but it is probably safe to assume that it will be at least 1mA, which works out to 1kV on input), excluding high voltage transient surges, which is what the Cat ratings are really about and should be handled by some kind TVS network across the inputs or after the first attenuator (in which case the series resistor of the attenuator might in fact behave like a fuse).
The current circuit is somewhat more complex for overload protection. Common solution involves placing two antiparallel accross the sense resistor such that the fuse will reliably blow before the sense resistor and following frontend (neat trick in many HP designs is using shorted diode bridge with the DC-side short being actively driven by voltage follower. This causes the diodes to be mostly fully closed outside of failure conditions and thus minimizes any non-linearities inherent in large power diode).
It's great to read about design judgment that takes off in terribly useful directions the market can't seem to follow.
Now, if you connected it to something above the specification of the meter or perhaps tried reading a voltage in ammeter mode, that's user error and completely your own fault and wouldn't have been prevented by autoranging.
Mine one is a cheap 35 euros analog multimeter and it's working fine since the last 12 years.
Just be careful and pay special attention when handling electricity.