Tiny Time Watch

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. It’s powered by a CR2032 button cell, and I’ve used several techniques to reduce the current consumption, so the battery should last for over a month. The total component cost, excluding the PCB, is about £5/$5, and it’s straightforward to build.”