Keychain

KeyChainino is an open source programmable 6x5 LED matrix keychain developed by Alessandro Matera. Powered by single coin cell battery, it provides 2-button user interface and enables to play simple games or display text. On the hardware side, it utilizes Charlieplexing for driving 30 LEDs with only 12 GPIOs! It runs on ATtiny84 microcontroller and is programmable via Arduino environment.

I didn't like the original PCB design because the hole of the keychain was on the top side of the board. In my opinion it is more convenient to hold keys in your palm while playing with it, so I decided to design my own PCB. Additionally, I added a power switch to reduce idle power consumption.