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 $_$)
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...)
In order to meet the ring size, I choose CR1220, I expect it can last over half an year.
(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)
(Quote from previous project) It should be more stylish if make it by wood, but I am lazy one, so just print it out.
(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.