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Ultrasonic Sensor Module (HC-SR04)

../_images/23_ultrasonic.png

The Ultrasonic Module(HC-SR04) is a sensor that can measure distances between 2cm and 400cm using ultrasonic waves. It is commonly used in robotics and automation projects to detect objects and measure distances. The module consists of an ultrasonic transmitter and receiver, which work together to send and receive ultrasonic waves.

Principle

The module includes ultrasonic transmitters, receiver and control circuit. The basic principles are as follows:

  1. Use an IO flip-flop to process a high level signal of at least 10us.

  2. The module automatically sends eight 40khz and detects if there is a pulse signal return.

  3. If the signal returns, passing the high level, the high output IO duration is the time from the transmission of the ultrasonic wave to the return of it. Here, test distance = (high time x sound speed (340 m / s) / 2.

The timing diagram is shown below.

../_images/23_ultrasonic_principle.png

You only need to supply a short 10us pulse for the trigger input to start the ranging, and then the module will send out an 8 cycle burst of ultrasound at 40 kHz and raise its echo. You can calculate the range through the time interval between sending trigger signal and receiving echo signal.

Note

It is recommended to use measurement cycle over 60ms in order to prevent signal collisions of trigger signal and the echo signal.

Formula:

  • us / 58 = centimeters

  • us / 148 = inch

  • distance = high level time * speed of sound (340m/s) / 2;

Example