LED Life and Charlieplexing

Yesterday, we featured [Andrew]‘s orientation aware camera. We want to highlight another one of his projects: LED Life. It’s a 6×5 LED matrix playing Conway’s Game of Life. He used the low power MSP430 like our e-paper clock. The best part of the writeup is his explanation of how Charlieplexing works. Microcontroller GPIO pins generally have three possible states: output high, output low, and input. This combined with the directional nature LEDs and some creative wiring means you can run a large matrix of individually addressable LEDs with just a few IO pins. Instead of just flipping the IO pins on and off you change their assigned state. Have a look at [Andrew]‘s site for some great illustrations of how the system works. A video of his LED Life board is embedded below.


  1. pip says:

    Yay!! More wasting electricity!


  2. Fwirt says:

    Cool idea… I actually thought that this instructable had a more complete explanation of how charlieplexing works:


  3. amk says:

    uhoh … better duck eliot. last time i mentioned charlieplexing in comments I was beaten with the “not a hack” stick.

  4. tony says:

    Thats a really interesting way to use the GPIO of a MCU. I would have never thought to utilize the input state to control an output.

  5. pc486 says:

    andrew had issues bending plastic, but my favorite plastic provider offers a kit and an instructional video on how to make really good looking bends:


  6. gyro_john says:

    Charlieplexing – that’s my free education for the day. Thanks a lot for posting this.

  7. Someone says:

    This charlieplexing is very interesting, only drawback seems to be that he only turns on one LED at a time. Of course (he mentions it) he could lit up more than one at a time, but probably this will soon draw too much power. Amplifier stage would be necessary then (and a more complex one than for normal matrix multiplexing), killing the simplicity of the design.

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