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