I saw all of these POV projects and i tought if i can build something small enough to fit on my wrist. So i built this watch. It is bulky and pretty useless but at least it works. Check the video to see how it turned out.
I'm using atmega32U4 as a processor with 7 LEDs connected trough resistors to MCU. I also have DS1307 to keep time of time and IR sensor to calculate RPM. That's everything on the PCB. The PCB is mounted on a DC motor from DVD drive and around that motor is li-po battery, step-up converter, transistor for the motor and some weights to keep it balanced.
The watch has 150mAh li-po battery which can last for couple of days since time is only displayed when a button is pressed. arduino goes to sleep when watch isn't being but the circuit still takes about 1 mA just to step the voltage up to 5V. therefore i have put in switch to completely turn off everything expect RTC so it can keep track of time.
For the construction i've used 3D printed parts and cheap watch that i took apart for the band. anyway I think it turned out great but i'd like to hear what you think about this and what you would differently or improve.