Drum machine / sequencer being developed in Kicad 8. Open source and free to use, based mainly on Roland TR808s, etc. As simple as it gets--- nothing to produce fancy attack/delay. This is meant to be as easy to understand and low-cost as possible. I'll be writing in notes as I develop the system on what math I'm using to determine components :).

White noise generation with transistor breakdown accredited to Moritz Klein!