I designed and wired two LED matrix clocks that display the time using an 85 LED matrix. The anodes of each row and cathodes of each column are soldered together, and the LEDs are individually addressable through a technique that utilizes multiplexing. The clocks are controlled by small Arduino microcontrollers, and their outputs are expanded by daisy-changed shift registers. Both clocks keep accurate time using DS3231 precision clocks, the battery of which keeps time for months. For the second version, I used my laser engraver to create a PCB that took care of most of the wiring. I learned how to use Eagle to create a circuit diagram which allowed me to generate the board layout.
