DIY Smart Coasters Tell You What You Already Know
Smart Coasters are plastic coasters with embedded LEDs 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 are powered by a solar cell so that the whole thing is hermetically sealed, making them waterproof and washable.
These aren’t for sale. Rather, they’re a DIY project from The Hungry Scientist Handbook. Complete step-by-step instructions are available for both the electronics and the resin casting. Full instructions to build your own can be found in The Hungry Scientist Handbook (which runs about $12 at Amazon).
The question now is, do you care enough about the novelty of the coasters to make it yourself. We sure don’t see anybody actually needing a little LED to tell them if their drink is hot.