What is charlieplexing technique?

If one has seen the Arduino Uno R4 board LED matrix arrangement, once can see a 12x8 matrix controlled by only 11 signals from RA4M1 microcontroller. This is possible through a technique called charlieplexing. Charlieplexing is a technique used in circuit design to control multiple LED with as few pins as possible from microcontroller. In a traditional LED circuit, each LED would require its own pin for control. However, with Charlieplexing, you can control multiple LED using fewer pins. Charlieplexing is a clever technique for saving pins, but it can become complex as you add more LED. Care must be taken with the software to ensure that the LED are being driven correctly and that the timing is sufficient to avoid flicker.

So, what is charlieplexing technique is that if there are 'N' number of pins available in microcontroller, up to (N^2)-N LED can be controller. This meant in Arduino Uno R4, for 11 pins, 

(11^2)-11 = 121-11 = 110 LED can be controlled.

We have 12x8 matrix which meant 96 LED which is within the 110 count.

One has to understand that with higher LED count, Charlieplexing technique brings wiring complexity as well.

Charlieplexing technique is described in our YouTube channel. Here is the link.