• grue@lemmy.world
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      3 days ago

      You put an Arduino-compatible microcontroller on a custom PCB, obviously. A QFN package ATTiny is like 4mm square.

      It’ll all be SMT parts if you want it to be watch-sized, so you’ll have to let JLCPCB or whoever assemble the board for you instead of soldering it yourself, but it’s surprisingly accessible to random hobbyists these days.