Hot Yet? This faucet water monitor will prevent plunging your hands into cold water
Attiny85 Faucet Water Temperature Sensor
Real life testing in the kitchen sink! Note the tri-color LED. Blue is cold and fades into Green which then flips to increasing Red at 85F.
JLCPCB – Prototype 10 PCBs for $2 + 2 days Lead Time
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Inside a huge PCB factory: https://www.youtube.com/watch?v=_XCznQFV-Mw