David Johnson-Davies’ minimalist ATtiny85 wrist watch displays time using 12 LEDs that are arranged in a circle like a watch dial. A push button, installed on the top side of the PCB, needs to be pressed to see time. The watch shows the hour by lighting up an LED and minute by flashing another LED. The minute resolution is 5 min.
To show the time you press the button on the watch face, and the time is then displayed for four seconds. It lights one LED to show the hour, and flashes another LED to show the minutes to the nearest five minutes, like the hour and minute hands on a clock. If only one LED lights up you know that both hands are pointing to the same hour mark.
The Tiny Time watch uses the ATtiny85’s built-in oscillator, fine-tuned to get it as accurate as possible, and my watch keeps time to within a couple of minutes over 24 hours. You can adjust the time by holding down the button for more than four seconds.