No pin is left unused between the DS18B20 temperature sensor, the surface mount seven-segment LED displays, and the ATtiny84 driving it all. With the temperature flashing every 24 seconds and the ...

The brains of the operation is an STM8S103F module, aka the Blue Pill, which is paired with a DS18B20 temperature sensor. [Tim]’s original coaster has one in a TO-92 package embedded in the top ...