[Robert Mibus] took on a project which his kids could present to Mom on Mother’s Day. It’s an LED heart built into a ring or necklace box. The series of white LEDs are animated in a chase pattern. The project let [Robert] push his comfort boundaries by moving past a stock Arduino board.
Inside you’ll find an ATtiny85. He picked up the chip to try running Arduino sketches on smaller hardware. But the total of five available I/O pins presented an issue with driving the LEDs. Ten LEDs are used here and even a standard multiplex display would need no less than seven to control them without additional chips or the need for Charlieplexing. His solution was to drive two opposite LEDs at once, which cuts the need down to his five available pins.
Once he got it all soldered together he realized that he had made a coding error. But a few soldered wires let him reflash it in place using ISP.