My analog synthesizer lacks a drum machine. I suppose you could just Moog DFAM or (clone), but… A few thoughts towards a project, assuming you are not an analog purist and have a Raspberry Pi Pico floating around…

Circuit design

A handful of 2k resistors is enough to build a two-channel 1 Hz-20 MHz wavegenerator using the programmable IO pins.
Or drive the good-old MCP4728 Quad DAC DATASHEET at 100 kHz, which is far beyond what I can hear. Heck, I’ve even got three free channels left on my MIDI-to-CV project that could be used for separate drum signals. This type of direct digital synthesis can be done efficiently, based on what appears to be an excellent digital systems design course at Cornell, with comprehensive lecture videos
Or go sample-based with a PicoAudio I2S pack I’ve got one of these kicking around the house, which I used for a Markov-chain music composition project…could also just program some wavetables for this. Might be the easiest path…potentially as simple as IO
- I2S audio can get really cheap (just a few bucks)
- I2S is in a preview for Micropython v1.19 so limited demos exist…or else you have to use circuitpython
- There are some decent CPP demos
Really fancy: PicoADK uses Vult to define DSP functions

Inspirations/Resources

digital-synthesis drum machine
If one gets inspired by the classic TR-808 analog drum machine the signals have the form of: drum: decaying sine wave; snare: noisy decaying sine wave; cymbal: white noise (can tweak this with a PRNG)
Kurt Werner did a phd in simulating analog circuits, including the TR-808…and led me into a rabbit hole of 1-bit music
Euclidean rhythms, naturally… (see also post)
Teensy-based drum machine — looks like C-code describing the various audioparameters and how they play with the switches and potentiometers
Polaron –teensy-based drum machine, nice interface, sequencer, c-code, open-source
MadLab Funky Drummer is a simple PIC-based 8-bit drum machine (sounds pretty OK); the inventor’s webpage has a schematic and Elektor article for an earlier version
The bleep drum was a simple kit that is no longer sold…but you can find the 22kHz drum samples online at github; this seems like a popular backend for kits like the cumbia tropical drum, etc.
PicoTouch capacitive midi keyboard and PicoStepSeq designs. Some inspiration for UI.
CRUM Drum is a neat little semi-generative 4-voice drum machine; driven by a (pre-programmed) Teensy

Other random thoughts

Tayda electroncis has some nice parts for making this shiny.
binaural beat generator — might be a good project along the way, regardless of how it is implemented. That said, one should be able to run the stereo I2S through separate channels

On second thought

(20 Apr 2024) Mortiz Klein has a new series of videos/kits for drum machines
(10 May 2024) Wavetable drum machine/sequencer based on ESP32

Prototyping hardware

spark inducer is pretty cool for prototyping eurorack stuff. It’s a chassis that provides power, knobs, and plug entries on a breadboard.

Sequencing (15 May 2024)

Use a clock + clock dividers to generate rhythms
- There are definitely kits to do this but the Doepfer A-160-2 is the classic (not too pricey)
- You want to think about sending trigger pulses versus constant cycles, number of divisisions, CV inputs, possible internal clock.
Introduce patterns by binary pattterns (e.g., Numeric Repetitor)
- The discontinued Pittsburgh Time Runner has some interesting ideas

Retrospective: What I finally did (Aug 2024)

Built Mortiz Klein’s drum bundle to learn the circuits and ideas, but then got limited musically… (Also, as a side note, analog drum circuits are really complicated! )
Bought a Korg Volka Beat (16 step sequencer) and Pocket Operations book to go more musical. (Not exactly DIY, but has some hacking potential )
Bought an Akai MCP218 drum pad and enrolled in Melodics drum pad course to try to get a more intuitive musical sense (not at all DIY, but a realization that I was emphasizing the hardware rather than the music)