Multiplex vs Charlieplex

Mike said:

Well I think those are absolutely excellent Charlieplexed matrix applications. Since you're only lighting a set number of LEDs at any given time you can increase duty cycle, average current, and brightness dramatically simply by using a carefully designed driver. Nicely done.

Cheerful regards, Mike

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Hi Mike, the most LEDs I have attempted to appear to be lit at once - of course they simply cycle very fast - is 39. This is in a 7 segment display clock made out of individually addressable LEDs. I am very happy with the result, I get no visible flicker or changes in apparent brightness. It's rock-steady and very bright indeed.

Very nice John.

I admit I cheat and use column driver transistors to increase duty cycle. For example, here's a Charlieplexed matrix of 20 LEDs with a 781-Hz refresh rate (8 MHz clock) and 20% maximum duty cycle per LED. Each LED is adjustable to 64 gamma corrected brightness levels spanning 256 PWM steps (1-usec steps) for smooth fade capability. In the video below, the LEDs in the left column are lighted for 1 usec (top) to 10 usecs (bottom) out of each 1280 usec period. Unfortunately, the LED wavelength is such that it overloads and saturates the camera and picture quality suffers accordingly.

Cheerful regards, Mike

[video=youtube_share;9PNHyJdpUVs]http://youtu.be/9PNHyJdpUVs[/video]