(Image credit: element 14 via YouTube)
LED wristwatches are still popular even after 53 years since Hamilton Watch Company and Electro-Data introduced Pulsar, the first LED (or digital) wristwatch. Clem Mayer of Mayer Makes is also a fan of LED watches and recently created his own using an ATtiny412 microcontroller that displays time using distinctive patterns.
Clem designed his “dumb watch” using the ATtiny412, due to its compact size and low power consumption, however due to its limited I/O, he ran into some design challenges. To mitigate that issue, he chose to incorporate an MCP7940 real-time clock (RTC) module via the I²C interface. The RTC helps maintain time even when the main power is off, thanks to its battery backup.
Clem’s watch face is outfitted with 24 LEDs that illuminate through an opaque surface, forming recognizable shapes that represent hours and minutes. The unique face allows users to tell time at a glance once they become familiar with the patterns. 12 LEDs show the hours, and twelve others show the nearest 5-minute increments, something similar to some analog watches.
The end result of Clem’s design offers an innovative, energy-efficient wristwatch despite the limited hardware. Those interested in building their own, can visit Clem’s project walkthrough on element 14’s webpage, which also offers links to his 3D printing files, KiCAD schematics and Arduino-based firmware.