10 Cent Music Machine I built a tiny coin‑cell music board around the $0.10 WCH CH32V003J4M6 (8‑pin, 48MHz RISC‑V, 16K flash/2K RAM). The PCB is just 16.3×11.7mm with a piezo buzzer and transistor, and in standby it sips 7–8µA. I did hit a snag: playback caused 130mA peaks that browned out a CR2032. A LiPo fixed it, but I really wanted coin‑cell, so I upped the buzzer’s base resistor to 10k, dropping peaks to 56mA and average to ~7mA—now it runs happily (and loudly) from a coin cell. Pro tip: if standby bricks programming, wlink can erase via power-off mode. I’m bit‑banging audio, published... 12 October 2025
High voltage coin cell I blew up the original PCB on a bistable cholesteric display, so I built a coin-cell Joule thief to crank out 27V and bring it back to life. A simple two-inductor setup with a 27V Zener does the trick—about 10 mA while the button’s held. Then I got fancy with a regulated version (just one extra transistor) that tops the cap to 27V and basically idles—average draw lands around 1.53 mA. It’s neat, tiny, and perfect for this low-current reset job. Full build and measurements are in the video. 26 September 2025