Case two part two a: MIDI-CV

I’m kind of surprised how few DIY MIDI/CV modules are out there. Befaco has one… LMNC has one, but it’s too powerful! It offers a lot of functionality I currently would not use, and its 100 mm width would be wasted on me. There’s not much else, but there’s the Erica Synths one. I believe their DIY stuff is no longer in production but they and SynthCube have stock, and anyway they’ve open sourced the design. So I might just get the board fabbed, especially if I decide their board’s form factor doesn’t work well with my Kosmo panel layout.

Case two part two

I’m rethinking this. There’s a problem with the Erica Synths MIDI-CV, which is that the hardware is open source, but the software is not. (The LMNC is closed source software too. I’ve just discovered the Befaco MIDI Thing is not closed source.) Erica Synths provides schematics, PCB layouts, and front panel design files, but for the software all they give you is the compiled .hex file. You can write that to a microcontroller chip, but it’d be pretty difficult to fix a bug, or to port it to a different architecture, or to add new functionality.

So maybe there are no bugs to speak of, and likely I’d never need to put it on a different chip, and maybe it has all the functionality I’d ever want. Maybe!

Maybe not. I’ve gradually come to realize I don’t really want to build modules for which a schematic isn’t available. Similarly, not having the software source code is crippling.

I’ve left a comment on the Erica Synths repository about this, but for now the source code isn’t open. Meanwhile, I rediscovered something I’d seen before but forgotten, elkayem’s midi2cv repository. Google turns up a number of homemade MIDI to CV projects, many of which are sketchily described and appear to have been abandoned at an early stage. Elkayem’s seems to have been completed and put into use. About two dozen people have forked it. Most of them have left it unchanged but a couple have pushed their own modifications, evidently having built a version of it. The schematic looks reasonable and the code looks pretty clean. It’s built around an Arduino Nano, which is not the most efficient way to go but is easy to work with.

So I think that’s what I’ll be using. I did my own fork (actually I forked one of the modified forks) and proceeded to work on it. I converted the Eagle schematics to KiCad and cleaned them up. I added Kosmo/Eurorack power, another output, and an option for an OLED display and push buttons to allow more configuration possibilities. I probably won’t use the latter on the first build. But they and the added output are the kinds of things I can only do because I have the source code I can modify to support them.

My fork is here. (Nothing’s tested, assume nothing works!)

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