A Charlieplex display and a board layout tip

[Ben] is getting himself up to speed with microcontrollers. He jumped into the deep end by taking on this Charlieplex LED matrix build. As you can see after the break, he not only made the display work, but coded Conway’s game of life to run on the ATtiny85 that drives the device. What you see above is the prototype version that [Ben] used to make sure he had the hardware just right. He’s seeing the project through to a manufactured board and this is where the layout tip comes from. In order to make sure he had enough space for all of his components he printed out the board artwork, taped it to some Styrofoam, and then inserted all of the through-hole parts. Now he can be sure that physically the design works, we’ll keep our fingers crossed that everything is also kosher electrically.


  1. Apexys says:

    Didn’t know charlieplexing needs that few wires.
    Cool hack!

  2. Ben says:

    Yup, you can control a lot of LEDs the higher you go. If you have X wires, you can control (X*(X-1)) LEDs… so 5 wires = (5*4) = 20 LEDs. But you can only light one at a time. I imagine if you try to run too many at once you might see some flicker.

  3. xeracy says:


    was gonna copy/paste, but theres good pictures of examples.

  4. Apexys says:

    It is really a great technology!
    But the wikipedia article is a bit to complex for me. The description Ben wrote is easier to understand.

  5. roboman2444 says:

    +1 for the game of life stuff in the vid

  6. Slanderer says:

    @Ben : The flickering really isn’t an issue. However, “ghosting” can be an issue (ie, extra LEDs dimly lighting). Furthermore, if one LED fails, you’re boned.

    With regard to strobing LEDs, its perfectly fine if the refresh rate is high enough. Simply make the pulses brighter, and you can decrease the pulse width required. A lot of LEDs have specifications for driving w/o a resistor at a certain PWM width (such that the self-heating due to internal resistance is within specs), which means you can maximize brightness for a short pulse, perfect for strobing.

  7. Spork says:

    All you need is reflective lenses for your strobe-LED’s and you could have a non-lethal weapon!

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