Main Features:
1. Brand new Ultrasonic Sensor HC-SR04 Distance Measuring Module
2. Features 4-mode connections: VCC / trig (T) / echo(R) / GND
3. With electric frequency output signal from 0V to 5V
4. Has high precision up to 3mm
5. 5VDC power supply
6. Detecting distance is from 2cm to 450cm

Module Working Principle:
1. Adopt IO trigger through supplying at least 10us sequence of high level signal
2. The module automatically send eight 40khz square wave and automatically detect whether receive the returning pulse signal
3. If there is signal returning, through outputting high level and the time of high level continuing is the time of that from the ultrasonic transmitting to receiving