This IoT Coaster Sends a Notification When the Tea Is at the Right Temp

Ben Cox is British, and therefore has strong opinions about his tea — specifically the acceptable temperature at which to drink it. Anything above about 55°C is too hot and results in a burnt tongue, and anything below about 40°C is too cold. The problem is that it’s easy to forget about his mug of tea while Brian is waiting for it to cool down to that window, and by the time he remembers to check it, it’s already undrinkably cold. So, he built an IoT coaster to notify him when his mug of tea was at the perfect temperature.

To do that, he first had to find the best place to measure the current temperature. With a FLIR (Forward-Looking Infrared) camera, he was able to determine that the entire bottom surface of the mug had a consistent temperature. With that in mind, he designed and 3D-printed a coaster with a small opening for an infrared temperature sensor. When the mug is resting on the coaster, the sensor is able to read the temperature on the bottom, which is close enough to the temperature of the tea to work.

The temperature sensor is read by an ESP8266 that’s placed inside of the coaster. A small webserver runs on the ESP8266 and exports the temperature data in the Prometheus format. A Grafana applet takes that data and graphs it so that Cox can always see the current temperature. From there, it was easy to add an alert when the mug reaches the top end of the temperature window, and have that alert delivered to Cox’s Discord chat room. Now Cox is notified the minute his tea becomes drinkable, and never has to suffer through cold tea again.