✍Ultrasonic ranging module HC-SR04 provides 2cm - 400cm non-contact measurement function, the ranging accuracy can reach to 3mm. The modules include ultrasonic transmitters, receiver and control circuit. If you are sourcing for an ultrasonic ranging module, the HC-SR04 is a good choose. Its stable performance and high ranging accuracy make it a popular module in electronic market. Compared to the Shap IR ranging module, HC-SR04 is more inexpensive than it. But it has the same ranging accuracy and longer ranging distance.

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▼The basic principle of work:
Using IO trigger for at least 10us high-level signal,
The Module automatically sends eight 40 kHz and detect whether there is a pulse signal back.
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


▼Specifications:
Power supply :3.3 ~ 5V DC
Quiescent current : <2mA
Effectual angle: <15°
Resolution: 3 mm
Sensing distance: 0.75in (2cm) to 13ft (4m)
More precise measurements with ranges up to 6.5ft (2m) away; Resolution : 0.3 cm

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▼ There are 4 pins out of the module : VCC , Trig, Echo, GND. So it's a very easy interface for controller is to use it ranging. The process is: pull the Trig pin to high-level for more than 10us impulse , the module will start ranging ; finish ranging , If you find an object in front , Echo pin will be high level , and based on the different distance,it will take the different duration of high-level.