Driving LEDs using the lowest possible pin-count is a common challenge for folks creating projects with microcontrollers. Complementary LED drive, also known as “Charlieplexing,” allows a large number of LEDs to be controlled with a relatively small number of I/O pins. This fun digital LED clock project is a hands-on example of how Charlieplexing can be used to stretch your “pin budget”!
Part 1 - The test circuit, using Charlieplexing to individually control 182 LEDs with only 14 I/O lines, and reading four pushbuttons by connecting them to the LED matrix with a handful of other discrete components.
Part 2 - Finishing the circuit, making the printed circuit board, building the clock, and how the software works.
This attractive timepiece is an ideal project for the serious electronics hobbyist. There are a lot of parts, but they are all through-hole and easy to solder. If you decide to take the plunge and make this clock yourself, when you’re done, you can proudly display your handiwork on your wall and enjoy it for years to come. You can gather all the parts yourself and fabricate your own frame, or get the kit from the Nuts & Volts webstore. A partial kit is also available.
