For questions about the HC-SR04 ultrasonic ranging sensor.

The HC-SR04 is an ultrasonic ranging sensor capable of measuring distances in the range 2cm to 400cm. It has a ranging accuracy that can reach up to 3mm under ideal conditions. The HC-SR04 module includes an ultrasonic transmitter, a receiver and a control circuit.

The HC-SR04 module has four pins: VCC (Power), Trig (Trigger), Echo (Receive), and GND (Ground).