In the block two LEDs (Light Emitting Diode) are housed. In addition, a series resistor of each 2.2kOhm is used to protect the diodes against excessive current flow. They are optimized for 2mA current. The resistors are connected to the other side of the brick and out separately, so that there can also build circuit variants. If one couples the resistance to a ground block to 0V he let be operated directly with the outputs of the Nano. Generally it should be ensured that the cathode must be connected negatively with respect to the anode. The cathode is marked with a slash on LED diode symbol.