Module tester v2


Hi Emilie - thanks for updating the module tester! Such a cool, useful tool…


Ha ha, I’m just tired of receiving one or two from the factory for repair while they are just using the wrong kind of wallwart.

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But yeah it’s a very efficient and trusted tool, the most used piece of equipment in my lab. My unit is 7 years old, has been left powered on for entire week-ends (oops) and is still kicking – I just had to replace the encoder once.

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I love mine ! I keep trying to think of ways to improve it! But it’s hard - it’s so useful! I am currently laying out a smt version in eagle with a smaller display with the aim of adding a headphone amp and mult - looking to add 1v/oct as well… as well as try to look at software calibration of the dac to improve accuracy…

Just bought another dac, screen and mcu to try to breadboard adding the 1v/oct and play with the software. I’m still learning so would be keen to know if this is a bad idea (ie not possible with the hardware - I think it is doable… but could be very wrong about that!)


Do you mean getting a 1V/O input to play tones or calibrate a CV output? That would be hard with the 8-bit ADC built into the AVR. You’d better use an external ADC (say an MCP3202).

As for improving accuracy of the DAC output to really hit 1.000V and 3.000V, yes it’s possible in software, you have to dither the DAC output (at the cost of a loss of output sample rate).

The test fixtures for the recent digital modules (starting from Plaits) use a MCP4822 for the 1V and 3V calibration CVs. There are no trimmers, it’s only software calibration, and I use 4x dithering to get 2 extra bits of precision.


1v/oct to play tones… (I was sort of thinking about putting together a mini tester rack with a racked module tester, mult, headphone adapter, adding 1v/oct for notes, adding a trs midi connection). I was looking at your calibration code in other modules for ideas. Thanks a lot for the info…


The module tester was the first DIY eurorack related thing I built, from a PCB ordered from the old Mutable web shop. It has subsequently facilitated building countless DIY modules, perhaps the most useful thing I’ve DIY’d.


Did you have much electronics experience before tackling this? I’m slowly getting into diy and am curious about the difficulty of this build - looks like a lot of parts but I have no idea what to expect.


I did have some electronics experience - but, I would say that this project is pretty good for a starting project. The PCB is large (easier to work with than a tightly packed euro module), and all the parts are through-hole. I think the most difficult part of this project for a beginner wouldn’t be soldering the board, but sourcing the parts, and programming the microcontroller chip if you don’t get one preprogrammed (aka ‘pre flashed’). There are no rare pars per se, but sourcing parts is always a pain the first times through. Similiarly programming the microcontroller isn’t difficult, but has the potential to be frustrating the first time through without help. If you want, the parts annoyance can be solved by purchasing a ‘parts kit’ or sourcing from a Mouser BOM (assuming the parts on the BOM are in-stock or else you’ll have to do a bit more work to swap in equivalent parts). The chip annoyance can be solved by buying a chip pre-programmed. You’ll also probably want an enclosure, at the time I built mine I had access to a laser cutter and laser cut an acrylic case from the .EPS file in the Mutable Instruments GitHub ( If you don’t have access to a laser cutter you could also send the file to an online laser cutting service.

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Thanks for the pointers! I’ll definitely be giving this a shot soon.

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Good to see the venerable Module Tester getting some love. My old v1 version is super-useful. It’s currently powering the two Westlicht Per|former modules I’ve been building, and I’ve used it to test every other module I’ve built for the last few years.