Over the decades we have seen many DIY clocks and wrist watches presented, but few are as likely to get you either drawing in the crowds, or quietly snickered at behind your back, as a binary watch of some description does. A wrist watch like [qewer]’s qron0b project which also uses BCD encoding to display the current time is among our more rare project types here, with us having to go all the way back to 2018 for a similar project as well as a BCD desk clock.

As is typical, a single CR2032 coin cell powers the entire PCB, with an ATtiny24A or compatible as the MCU, a DS1302 RTC and the requisite 4×4 LED matrix to display the hours and minutes. Technically three LEDs are unneeded here, but it looks nicely symmetrical this way, and the extra LEDs can be used for other tasks as the firmware is expanded from the current setting and reading of the time.

The AVR C firmware can be found in the above linked GitHub repository, along with the KiCad PCB project and FreeCAD design files for the watch body. The body accepts a 22 mm GT2/GT3-style watch strap to complete the assembly. With a single CR2032 you’re assured of at least a few months of runtime.