Where I am from it is sometimes very difficult to source components for digital Eurorack modules, but I had my eyes on Peaks for a long time and I wanted to do something cheap with the same functionality. The basic premise was to use a bluepill (stm32f103c8t6 development board) and omit the DAC IC, relying on a technic called dual PWM as it is described in openmusiclabs blog and used, for example, in the popular Mozzi Library for Arduino.
The project uses a single sided home-etched PCB with a couple of jumper wires, the potentiometers are regular 16mm ones mounted at the side, also helping with the mechanical stability of the build.
You will need a bluepill capable of 128kb of flash, I bought mine advertised as only having 64kb, but it ended up not being the case, so it's worth the try
There's the option to flash one of two firmwares that where ported. The original Mutable Instruments one is in the firmware/peaks directory. The Mutated Mutables Dead Man's Catch is in the firmware/peaks2. The later adds a lot of functionality to the module, although the UI becomes a bit confusing.
Compiled binaries and HEX files are provided for both under firmware/build.
- Added a driver for the PWM DAC running at 14 bit depth, 48Khz sampling rate. (File in firmware/peaks/drivers/pwm_dac.h)
- Activated the clock for the TIM4 in firmware/peaks/drivers/system.cc
- Bypassed the bootloader: This was done as to simplify the code, it does not interfere with the calibration functionality of the module.
- Redesigned the output portion of the hardware to accommodate to the PWM levels.
Flashing and development
To make it easier I have left binaries and .HEX files in firmware/build, this can be flashed directly to the bluepill using STM32CubeProgrammer.
Another option is to install the mutable-dev-environment and replace the peaks folder with the one inside /firmware, then executing
make -f peaks/makefile upload_serial
We use this command because the bootloader is bypassed.
I want to thank Emilie Gillet for open-sourcing her work which is a constant inspiration for many musicians and makers, and encourage everyone interested in this project to checkout the Mutable instrument's Forum in which Emilie is a very active member.