This instructable show how to use an ATtiny85 to create a tiny watch core that can run over 1 year before recharge or replace battery.
The instruction to make the watch case may be in next instructable.
I have made a few Arduino watch before, but I found the watch using ATmega boards or ATmega chips are a little bit too big to wear. So I would like to make it with a smaller chips.
I have choose ATtiny85 just because I can easy to get one.
The challenges for using ATtiny85 are:
I design to develop a tailor-make code to complete these challenge, it include:
Today core subject, ATtiny85.
Any ISP that can program ATtiny85.
In general expectation, a watch should run over 1 year without charging or replace battery. For my simple measurement of power usage and the battery specification, CR1220 can only run about half an year, CR2016, CR2025 and CR2032 can run over 1 to 2 years representatively.
Since the number of IO pins of ATtiny85 is very limited, I design display and further modules should all run in I2C. Power consumption and source availability are also important factors. I choose an OLED screen drive with SSD1306. It can find in 3 different sizes, 64x32 is the smallest one. (another sizes are 128x64 and 128x32)
A battery holder, a small bread board, some bread board wires, two buttons and a power switch (optional).