Build a Microcontroller C.V./Trig Thing Workshop

There seems to be interest over in the Serge thread in folks building the small microcontroller c.v. and trigger unit I made this month:


  • 4 control voltages out, 0 ~ +8V, ~2kHz max bandwidth
  • 4 trigger outs, 0 ~ 8V
  • Based on a Feather M0 board
  • Optional display
  • Programmable in C++ or Circuit Python
  • I made it for Serge, but could easily be adapted for Eurorack.

Here’s it being a sine LFO:

I’m running a MIDI looper on it - so it can easily be a USB MIDI device, but with a little coding you can make it be anything you want.

I’m game to run a workshop pandemic style, that is, all on line: As group we’ll work through the schematic, parts, building, and coding together - tweaking or customizing the design as we go… I’ll supply the initial design, walk people through the build, (there are some construction tips that made the final thing nice), and help with coding.

I think this makes an absolutely great medium project to build, requiring only simple soldering, and some physical hacking for your enclosure. The coding is pretty easy, and I’ll supply working starting points.

Workshop site:

Workshop plan:

  1. review the schematic
  2. overview of construction
  3. bill of materials / order your parts
  4. building
  5. code
  6. performances!

Who’s in?

Clarification: My aim is to run the workshop right here - in this thread! I’m willing to hold some zoom meetings as needed - but I think we do it mostly right here, without being on-line at the same time.


Totally in! Love the idea. Been wanting to build something similar for my serge but always nicer to do it with other people for me. Just not sure about time zones and all that.

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SO COOL! I’m totally in, thanks for your labor!

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Great idea, can’t wait for this!
May I ask why Feather M0 and not Teensy or Arduino?


Okay - we’re on… I’ve got about another day or two of editing, and I’ll have all the build information ready and on-line. Once that’s done, we’re off to the races, and I’ll post all the details right here!

@alexeydemidov - Short answer: I just know it well.
Long answer: I wanted ARM processing, decent RAM and Flash space, plenty of I/O, and small form factor. Feather M0 & M4 fit the bill. Adafruit has put in a tremendous amount of engineering to make these very easy to work with: UF2 boot loaders, libraries for the whole ecosystem of add ons that “just work” with these boards. I really appreciate their attention to detail. And, on top of that, their work is open source and open hardware.


Got it thanks, Adafruit are really great but bit on expensive side to get here (Thailand) but totally worth it anyway, just wanted to understand the reasons, looking forward to this project thank you.

This would be my interest…

though as i love DIY stuff an am curious about these type of boards i will definitely watch it all.
Request for 1 spoiler though: does it have a screen? ( edit: I see you have said ‘optional display’)

I am in! Thanks for putting this together, @mzero!

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I’m in! I’m fairly new to DIY, so this sort of forum / “workshop” seems so perfect. Thank you for doing this! clicks bell

Awesome, I’m also in! I got a bit stuck with my attempt to build a basic microcontroller/CV interface so this seems like the perfect time to pick it up again!

Let’s get thing off the ground!

Site with info:

The code and build instructions will come in the next week, schematic, layout, and parts are all there now.

Get your parts: You can head right to the parts page, and get going ordering your material. I made this from parts I had lying around… so:

  • Look to see what you’ve got. The parts list is fairly forgiving and you can substitute. If in doubt, just ask - others will want to see what works, too!

  • It will help to look at the pictures and layout pages on the site to see how things interconnect, and help you choose what you need to buy.

  • If you want to use a different microcontroller - let me know and I’ll investigate if it will work.

  • I think I got everything right in the BOM file you can download and use to order… let me know if anything is amiss, or if you found a better part, etc…

  • Remember you’ll need to connect this to your synth’s power supply. I don’t know what yours is or what connector it needs. So, remember to add that!

Mine does - it is very small. It is totally optional - all depends on what you want your code to do. You could also add a small encoder knob as well. It is totally possible to have this controlled entirely via the USB connection - as a MIDI to C.V./Trig converter, for example.

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Probably super basic, but I’m super new to buying parts and builds for projects like this, so I’m hoping someone can provide some guidance.

If I wanted to power via a Serge PSU and I already had the cable, what sorts of parts should I be looking to add?

Thanks so much for the guidance :bowing_man:

No worries!

Your PSU has some connector, usually female. Then you want a cable with the matching male connector at one end. The other end you can just solder to the perma-proto board (where we’re assembling the op amp circuits). This is what I did and you can see it here:

If you don’t want a long cable dangling off the end like that - you can get another pair of connectors and put them between the cable and the board.

The cable - BTW - needs only to be 2 conductor: +12V & GND. Mine has 3, as I already had the cable made… I’ve soldered -12V (white) to the board to keep it out of harm’s way, even though it is totally unused.

SO - if you have the cable already and it already has the right connector to connect to your PSU on it - you’re done! If you just have the cable - you’ll need the proper mating connector for your PSU.


That is SUCH a handsome setup. My equivalent would be a rats nest.


How’s everyone coming with their parts orders? Any questions or help needed? Choosing a microprocessor and need guidance? I’m here!

I’m thinking we could do a group “go over the schematic, layout, and build” perhaps on the discord server? Perhaps sometime this weekend?

Who’s in?

I’m still waiting on some parts, hopefully the beginning/middle of next week :crossed_fingers:t2:

Two things:

  1. Adafruit just announced a MIDI FeatherWing for adding DIN or 3.5mm MIDI! I think this is a well worth it addition to this project.

  2. I’ll be on-line on the lines’ discord to walk through the design & schematic, and talk about the build:
    — Thursday, 9/17: 6pm ~ 8pm PDT / 9pm ~ 11pm EDT
    — Saturday, 9/18: 11am ~ 1pm PDT / 2pm ~ 4pm EDT / 6pm ~ 8pm UTC
    (I realize it’s Rosh Hashana - so I can schedule another session if there is interest.)

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starting in 10min… over on the discord server:

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I haven’t had time yet to go through the parts list and order everything but I’ll do that as soon as possible!

Also, I’m still not sure if I’ll use the Feather M4 board or some other microcontroller. I’ve started learning Rust recently and programming a little CV sequencer would really make a nice first embedded development project. There is a library that offers Rust support for both the Feather M0 and M4, but the documentation is a bit limited, so I’m looking for some alternatives that maybe are a bit more accessible…

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I see support for the timer features in that library, which is what you need to set up the PWM for CV out. But, I don’t have any direct experience. If you are looking at a different processor board, I’d be happy to check it out and see if I think it’ll work from the HW perspective.