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 ...
[Wassim’s] interest in STM32 was spurred by the Blue Pill board–the $2 STM32 board and his desire to debug it. He found you often have to make tweaks to the IDEs to get them to work.