This is the HC-SR04 ultrasonic distance sensor. This economical sensor provides 2cm to 400cm of non-contact measurement functionality with a ranging accuracy that can reach up to 3mm. Each HC-SR04 module includes an ultrasonic transmitter, a receiver and a control circuit.
There are only four pins that you need to worry about on the HC-SR04：VCC（Power）, Trig（Trigger）, Echo（Receive）, and GND（Ground）. You will find this sensor very easy to set up and use for your next range-finding project！
This sensor has additional control circuitry that can prevent inconsistent "bouncy" data depending on the application.
