It runs at 8MHz and a 5v version at 16MHz, but 8MHz is enough.Overall, all you need to prepare are Arduino Pro Mini 3.3v and USB to UART module.
Bluetooth is to communicate with other devices, and the battery would be necessary for power.
I’ll install an Android app for collecting or editing various RSS and system information and for notification on the Android device.
You need to prepare modules as small as possible to wear the watch on your wrist.
I’d given lots of thoughts, then I chose -.96’’ OLED Display. Battery I use Li Po(Lithum-Polymer) battery in this project.
There are various sizes of the displays(0.96’’, 1.3’’, etc), it works on low-power, English font and the image out available, and it supports I2C, SPI, which makes easy to connect with Arduino. I used an 128×64 OLED which is using I2C and SSD1306 driver chip. 1-cell Li Po battery flows out current in 3.7v, which works perfectly with Arduino Pro mini, and there are many kind of batteries in terms of the size and the capacity.
You need to put ( ) line to RAW pin in case you use any sort of external power supply, such as an external battery, on Arduino Pro mini board.