HC-SR04 Ultrasonic Module Distance Measuring Transducer Sensor

Product features: 

Ultrasonic ranging module HC - SR04 provides 2cm - 400cm non-contact measurement function, the ranging accuracy can reach to 3mm. 

The modules includes ultrasonic transmitters, receiver and control circuit. 

The basic principle of work: 
   (1) Using IO trigger for at least 10us high level signal, 
   (2) The Module automatically sends eight 40 kHz and detect whether there is a pulse signal back. 
   (3) IF the signal back, through high level , time of high output IO duration is the time from sending ultrasonic to returning. 

Test distance = (high level time×velocity of sound (340M/S) / 2,