An ornament Sara and I designed for the 2019 holiday season!
The board consists of twelve reverse-mounted LEDs charlieplexed and hooked up to an ATtiny85. Each LED is individually addressable, even though only four of the ATtiny’s pins are being used (Charlieplexing is magic)! The board also has a pushbutton for switching between modes. The ornament is powered via six CR1225 batteries.
The final board isn’t the most elegant thing- there are several zero-ohm jumpers, and there’s even a “decorative” wire that wraps around the snowflake that is actually a ground line I didn’t want to route across the front of the ornament. Most of the layout was done on a train between Trenton and Boston, so give me a break! There are also a few outright mistakes- under each LED should be a rectangle on the f.mask layer so that the area below the LED is free of solder mask. Instead, the rectangle is a keepout zone, which is useless in this situation. My solution was to scrape the areas clear with a knife but I don’t recommend it because FR4 dust is nasty.