Project: Temp Sensing Coffee / Tea Sleeve

Last weekend I came down with a bad cold, so no circuit projects for me. However drinking a ton of tea gave me some inspiration for this week’s experiment – a coffee cup sleeve that warns you when your drink is too hot. I don’t know how many times I have been burned by super-hot green tea, so here is my fun little solution to that problem.

I’ve been wanting to play around with sensors, and while surfing the net one day I came across Aniomagic’s Learning Sensors. They are nice little sewable sensors that come in a few different varieties. The temperature one caught my eye because it is self-contained and you don’t need to hook up any external microcontrollers to play around with it.

Aniomagic's Temperature Sensor (image via )

Aniomagic's Temperature Sensor (image via


Aniomagic even has a cool tutorial for a temperature sensing coaster, which I ended up adapting for my coffee sleeve idea.

Aniomagic's Smart Coaster Project (image via )

Aniomagic's Smart Coaster Project (image via


For my project I used my favorite little bipolar LEDs from Electronic Goldmine as the eyes for a fleece Penguin. The temperature sensor is hidden behind his belly and lights the LEDs red if the temperature is higher than my calibrated preference, and green when it is ‘just right’. Once the temperature drops lower than my preference, the LEDs turn off. There is a 3rd output that I could have hooked additional LEDs to, but I liked the simple red/green communication as I am more concerned with the higher temps than my beverage being too cold.

This was a fun little project to wire up and I’m happy with the design. After testing it I found that the sensor needed to be pressed right up against the cup or it lost the reading, this can be solved by placing your fingers right on the penguin to keep the tension. I tried it out on some green tea, and I think I’ll bring it along on my next visit to my local coffee shop and see how it does with different beverages.

Check out some progress shots and details of construction below and on my Flickr account.