The IR Obstacle Avoidance Sensor Module uses an infrared emitter / receiver pair to detect obstacles in front of the sensor. This IR Obstacle Avoidance Sensor uses an IR emitting LED and IR Receiver pair to detect obstacles in front of the sensor by the IR Receiver detecting the IR that is bounced of an object by the IR Emitter. Per specification, the device can detect objects in the range of 2 to 40 cm in front of it.
The module operates at 38 kHz as the HS0038B receiver module is designed to specifically look for IR pulsing at a 38 kHz rate. The potentiometer next to the GND pin is used to adjust the frequency of the 555 timer and is set to approximately 38 kHz from the factory and shouldn’t be readjusted unless you have a scope or frequency counter to calibrate the frequency.