I don’t know if there are more popular, more pervasive watches than the Casio F91-W and A178-W models. I had one as a kid, like millions of other people, and loved it, but didn’t think much about it when I grew up. Until I met Joey Castillo and his project, Sensor Watch at the Hackaday Supercon 2022. Joey and the sensor-watch contributors designed a replacement PCB for those Casio models, with a programmable MCU and an extension port that could be used for example for a temperature sensor. I ordered 2 kits on the spot, this was too nerdy to pass on.
And down the rabbit hole I go. There are entire subreddits dedicated to these watches. Etsy stores for mods like OGGLOGG. At this point, I wanted to build watches for myself and my friends. And so I did:
