Building a wrist watch is quite a challenge, but when we want to squeeze electronics in to ring then real fun begins. It becomes even harder when using building blocks that are meant for prototyping. Anyway take a look at following instructable, where 陳亮 have put decent looking ring watch.
He had to squeeze Attiny85 microcontroller which comes in SOIC package. It’s been soldered on small prototyping PCB. Another large part of it is display. It’s 64×32 OLED display module with SSD1306 controller on board. Display is a biggest part of all and determines the ring width. Ring watch also carries s CR1220 battery with expectancy to last at least for half an year. Three push buttons gives ability to change settings. Time is counted internally and here helps Paul Stoffregen time function arduino library.
We recommend EasyEDA for circuit design and PCB prototype