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Charlieplexing : the art of getting more out of less
By booyaa | February 11, 2008
This weekend I got my head around Charlieplexing, well I kinda understand how it works now. I won’t try to explain the electrical theory behind, I’ll provide links at the end of the post that do a better job. I will tell you that Charlieplexing allows you to drive LEDs (or LCD segments) with less output pins, normally this relation ship is 1 pin to 1 LED. With Charlieplexing you can usually drive N LEDs where N is Y pins * Y-1.
I made two videos based on varying the mode of the pins (input or output) and sending high (+5V) or low voltage. You’ll need to visit my blog to see these. No source code today, it’s far too ugly to publish, as soon as I use loops to simplify the code I’ll share.
Chaser (one pin is always an input)
Two LEDs on at a time (all pins are outputs)
If you look closely you’ll see three yellow wires, which go to the three pins I’m using.
So far I haven’t worked out how to turn on all LEDs, I’m wondering if this requires some PWM jiggery pokery and flickering to fool into thinking the LEDs are all on?
Anyhoo here are the webpages that will explain Charlieplexing:
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