Multimeters are a bit like potato chips: you can’t have just one. But they’re a lot more expensive than potato chips, especially the good ones, and while it’s tempting to just go get another one when you need to make multiple measurements, sometimes it’s not practical. That’s why something like this 2×4 relay-based multiplexer might be a handy addition to your bench
In this age of electronics plenty, you’d think that a simple USB relay board would be easy enough to lay hands on. But [Petteri Aimonen] had enough trouble finding a decent one that it became easier to just roll one up from scratch. His goal was to switch both the positive and negative test leads from up to four instruments to a common set of outputs, and to have two independent switching banks, for those times when four-lead measurements are needed. The choice of relay was important; [Petteri] settled on a Panasonic DPDT signal relay with low wetting current contacts and a low-current coil. The coils are driven by a TBD62783A 8-channel driver chip, while an STM32 takes care of USB duties.
The mechanical design of this multiplexer is just as slick as the electrical. [Petteri] designed the PCB to act as the cover for a standard Hammond project box, so all the traces and SMD components are mounted on the back. That just leaves the forest of banana-plug binding posts on the front, along with a couple of pushbuttons for manual input switching and nicely silkscreened labels. The multiplexer is controlled over USB using the SCPI protocol, which happily includes an instrument class for signal switchers.
We think the fit and finish on this one is fantastic, as is usual with one of [Petteri]’s builds. You’ll probably recall his calibrated current reference or his snazzy differential probe.
Voltage and current measurements wont muliplex that well as the meters current measurment is a short circuit to voltage.
nothing stopping you from inventing your own voltmeter with a resistor and an ammeter
or, really, just having one meter for each; i assume that’s why it’s a 2×4 mux
I always like a project in a Hammond box rather than one off burnt wood or 3D printed boxes. Good work!
You say you use SCPI as a protocol, but where (which software) do you control the device from?
I use Python & Jupyter, it makes it easy to keep notes.
I have a couple of simple drivers here (which I’ll probably do a blog post about at some time): https://github.com/PetteriAimonen/labtools/tree/main/instruments
I thought of something similar to this, but is a manually controlled device, primarily for on-the-fly switching between my curve tracer, and multimeter. This project is a definite upgrade, good job on the control over USB.
@Clovis – Per the site linked, check here – https://github.com/j123b567/scpi-parser
Could probably get away with using pyVisa or something similar, perhaps? It’s merely the beauty of protocols and able to automate ‘things.’ I personally use pyVisa to automate a bunch of my test equipment, definitely have a look at that project, plus alternatives. Check out this small example, so much power to be had: https://pyvisa.readthedocs.io/en/1.8/example.html
I’ve done this before with manual switches for a test jug for the production crew. Works great.
I used to build test equipment like this,
I had a 24 x 4 cross point matrix out of electromagnetic relays.
We did something similar, except on a MUCH larger scale (like 256×8 I think it was) at what used to be “Ma Bell”). It’d be a good use for all those mercury wetted relays that we left over (filling a parts box I have no other use for).
(Let me know if you want some…)
That sounds like the one I used in the Air Force. F-15 Had 1024 pins on the front that could be hooked to power supplies, frequency counter, o-scope computer I/o, function generators and a number of other items. Made automated text of several lru’s much faster and way easier.