With a six-digit, seven-segment display such as the HDSP-2000 (itself an unusual choice – he hasn’t made this easy), Vitalii needed to find a way to multiplex the signals coming out of the chip, multiplying the I/O signals with transistors until he had enough to control each of the segments in the display. The result is this wonderful wristwatch, the custom PCB that enables the ATtiny85 to control the display, and a great deep dive into multiplexing written up on Hackaday.io.

We’re seriously impressed by this feat of electronic engineering. If you are too and you want to try it yourself, we’d suggest that you start with a single seven-segment display, a breadboard, and go from there – this tiny form factor presents loads of difficulties, all of which have been overcome here with aplomb.