Here’s a cool set of DIY colo-changing LED coasters. Basically, it runs on solar power, LEDs light up in red for hot drinks and blue for cold drinks.
Looks pretty simple to make, maybe a good idea for your next circuits projects.
Smart Coasters are cast-plastic coasters for your drink that light up red when you put a hot drink on top and light up blue with a cold drink. The design is fully analog– no microcontrollers and no programming– and they incorporate a solar cell so that the whole thing is hermetically sealed: waterproof and washable. Complete step-by-step DIY instructions are included for both the electronics and the resin casting.