Gorgeous seven-segment display that depicts numbers by heating and cooling

Thermochromic materials change color as they heat or cool. You know the mood ring? Like that!

Now comes a much weirder and more delightful use of this technology: A seven-segment thermochromic display. Each segment is blackish in color when cool, but slowly changes from reddish to yellow to green as it heats up.

Behind the scenes is some nifty hardware work by the physicist Moritz v. Sivers, as this post in Hackaday describes …

To achieve the effect, he first cut each segment out of copper. The crystal sheets were applied to the segments, thanks to their handy self-stick backing, and the excess was carefully trimmed away. Each segment was then mounted to a TES1-12704 Peltier module by way of thermally conductive epoxy. TB6612FNG motor controllers and a bevy of Arduino Nano's are used to control the Peltier modules, raising and lowering their temperature as necessary to get the desired effect.

It's pretty mesmerizing to watch in action, since the segments glow and recede so slowly — a witty inversion of the snappy speed at which we normally expect digital readouts to move. I'm now dreaming of having an entire wall of these things as the output for the world's most glacial word processor, where you have to voluntarily ease your typing speed down to 5 WPM so the display can catch up.