Watch enthusiasts pride themselves on finding rare or unique timepieces, and this DIY piece from Electronoobs fits that bill quite nicely. It’s a simple watch built around an ATmega328P microcontroller housed on a custom PCB with a dozen LEDs (with accompanying 200 Ω resistors) on its face. It also offers a single push button with a pull-down on the front to set the watch and to check what time it is (LEDs are not continuously lit).
On the backside of the watch, there’s a 3V button-cell battery socket along with a pair of pads for SPI and UART communication ports to burn the 8MHz internal clock bootloader and to upload firmware code, which is done using an Arduino Uno. Since there is no external clock source to keep the correct time, the watch uses an internal 8MHz oscillator, which is why you need to flash the bootloader.
While Electronoobs watch is an excellent project for getting acquainted with the ATmega328P, it does have a few drawbacks. The internal oscillator has a calibrated accuracy of +/- 10%, equating to 15-seconds every day as long as the watch has power, which is around 90 hours or four days before needing a recharge.
With that said, the watch is still unique and somewhat fashionable in a geek perspective. Those looking to build their own AVR watch, Electronoobs provides a complete walkthrough, complete with schematic files and the code needed to get it up and running from his website found here.