New Here - Charlieplexing Question

Hey Folks,

I’m relatively new to the goodness that is the Arduino and have been looking at getting the Arduino Mega. (yes I did search the forum for charlieplexing)

If my calculations are correct the Mega has the capability of Charlieplexing up to 182 LEDs with the 14 (of 54) Digital I/O pins the provide PWM.

Or, have I missed the boat completely with my calculations?

Should the calculation be:
//where N = N Pins
N * (N - 1)

Anywho, in time I hope to be a decent contributor to the forum.

Charlieplexing that many LEDs can be problematic because the number of LEDs that can be lit at any one time is limited by the current specs for the IO pins. That is, you can illuminate only 40mA worth of LEDs, cause they’re all sunk into one pin…

Theoretically you can drive up to 400 ma of leds if you can spread them over enough pins so no one pin is sourcing or sinking more than 40ma and no more than 200ma is sourced and 200ma sunk at one time.

But careful programming would be needed to ensure that the maximum ratings were not exceeded and running at the absolute maximum rating is not advised.

Theoretically you can drive up to 400 ma of leds if you can spread them over enough pins

Yes, but with charlieplexing (or multiplexing without drivers, for that matter), one pin has to sink the current for a whole “row” of LEDs. So even though you could drive each LED in the row with 40mA from the individual pins, the limiting factor is that the other sides of the LEDs all have to “fit” through one pin that also has the 40mA limit…

almost immediately after posting this I came across the CCShield. I think I’ll stack a couple of those together. :slight_smile:

I only need to drive 140 LEDs.

thanks for the replies folks.