Charlieplexing
When using charlieplexing, n drive pins can drive n digits with n-1 segments. When simplified, it equates to n pins being able to drive n2-n segments or LEDs. Traditional multiplexing takes many more pins to drive the same number of LEDs; 2n pins must be used to drive n2 LEDs (though a 1-of-n decoder chip can be used to reduce the number of microcontroller I/O pins to ).
If the number of LEDs are known, then the previous equation can be worked backwards to determine the number of pins required. That is, L LEDs can be driven by pins.
| Pins | LEDs |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 12 |
| 5 | 20 |
| 6 | 30 |
| 7 | 42 |
| 8 | 56 |
| 9 | 72 |
| 10 | 90 |
| n | n2-n |
Read more about this topic: Charlieplexing