MCU

Today core subject, ATtiny85. Someone suggest me to use SOIC version to reduce the watch size and I found the coin cell mAh calculation method will count the battery voltage down to 2.0 V, so this watch require a low voltage version MCU to keep it stable. So I have ordered an ATTINY85V-10SU. (much expensive $_$)

ISP

Any ISP that can program ATtiny85, this time I am using a Digispark act as a littleWire. (http://digistump.com/board/index.php/topic,160.0.h...)

Battery

In order to meet the ring size, I choose CR1220, I expect it can last over half an year.

Display

(Quote from previous project) 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 4 different sizes, 64x32 is the smallest one. (another sizes are 128x64, 128x32 and 64x48)

Watch Body

(Quote from previous project) It should be more stylish if make it by wood, but I am lazy one, so just print it out.

Transparent Cover

(Quote from previous project) A small piece of transparent PET plastic plate. It is transparent, provide enough support and very easy to get from many product packing.

Other Parts