This component houses two LEDs (Light Emitting Diode). In addition, a series resistor of 2.2KOhm is used to protect the diodes from excessive current flow. They are optimized for 2mA current. The two resistors are connected to ground. This means you can connect the brick directly to an output pair from the Arduino Nano Brick. In addition, the two signals are forwarded to the other end so that further controls can be carried out there.