The Infrared Obstacle Avoidance Sensor has a pair of infrared transmitting and receiving sensors. The infrared LED emits Infrared signals at certain frequency and when an obstacle appears on the line of infrared light, it is reflected back by the obstacle which is sensed by the receiver.
When the sensor detects an obstacle, the LED indicator lights up, giving a low-level output signal in the OUT pin. The sensor detects distance of 2 - 30cm. The sensor has a potentiometer which can be adjusted to change the detection distance.