I once purchased an electronics kit from Kitsrus called Heart of Love (kit 136) as a Valentine Day present. 15 years later, the Heart of Love continues to blink its LEDs in fun patterns. The kit includes source code and schematic. This repo contains a JavaScript port. Implementing this code gave me an opportunity to peek and understand how the flashing patterns were encoded. Interestingly, the original source code implemented an interpreter to save code space.
Next steps? Maybe I'll emulate the chip (an Intel 8051) or build a keychain-sized clone...
Visit k136.html in your browser to see the JavaScript version of Heart of Love.