Mega Tiny Time "Analog" LED Watch Works Without a Dedicated RTC

David Johnson-Davies of Technoblogy has been working on LED-based analog style watches since at least 2016, and his latest iteration looks excellent. This timepiece, dubbed the “Mega Tiny Time Watch,” features an array of 12 LEDs arranged in a circle around an ATtiny414 microcontroller, with a crystal for timing, a button to display the time, and a CR2016 battery on the back.

When the button is pressed, an LED lights up to indicate the hour, then one or two LEDs light up to represent the minute value. Cleverly, the minute LEDs blink five times in proportion to what actual minute it is, explained on the project write-up. The LEDs are controlled using just four I/O pins from the ATtiny chip, and the wiring is routed in a way that’s convenient, not necessarily in an incremental fashion with regards to numerical values. This, however, is easily compensated for in software.

Besides being a geeky fashion statement, the wearable device nicely shows off an excellent feature of 1-series ATtiny microcontrollers, which can act as real-time clocks (RTCs) via an external crystal. This arrangement should make it fairly easy to construct, and PCB files and code are linked on the writeup. If you’d like to check out an earlier version of the watch, here’s one that we featured some time ago which instead uses RGB lighting.