 A balance between complexity and pin use can be achieved by Charlieplexing several pre-built multiplexed LED arrays together.When using LEDs with different forward voltages, such as when using different color LEDs, some LEDs can light when not desired.In the diagram above it can be seen that if LED 6 has a 4 V forward voltage, and LEDs 1 and 3 have forward voltages of 2 V or less, they will light when LED 6 is intended to, as their current path is shorter.