This is the third in my series of minimalist watches based on the ATtiny85. This version displays the time by drawing an analogue watch face on a miniature 64×48 OLED display. It uses a separate crystal-controlled low-power RTC chip to keep time to within a few seconds a month, and puts the processor and display to sleep when not showing the time to give a battery life of over a year:
The Tiny Face watch based on an ATtiny85 and a 64×48 OLED display; it’s ten past ten.
To show the time you press the button on the watch face, and it displays an analogue watch face on the display, with a moving seconds hand. The display is automatically blanked after 30 secs to preserve the battery life.
Like my previous Tiny Time 2 Watch this watch is based on Maxim Integrated’s DS2417 RTC chip, a small 6-pin package which uses a 32.768 kHz crystal to keep accurate time . It can communicate with the main ATtiny85 processor via a 1-wire interface, which uses just one I/O pin to transmit and receive data. Because the RTC chip is doing the timing the ATtiny85 can stay asleep in power-down mode when it’s not actually displaying the time, dramatically reducing the power consumption.
for more detail: Tiny Face Watch