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Chapter 10 Ultrasonic Ranging
Chapter 10 Ultrasonic Ranging
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Component Knowledge
The ultrasonic ranging module uses the principle that ultrasonic waves will be sent back when encounter
obstacles. We can measure the distance by counting the time interval between sending and receiving of the
ultrasonic waves, and the time difference is the total time of the ultrasonic wave’s journey from being
transmitted to being received. Because the speed of sound in air is a constant, about v=340m/s, we can
calculate the distance between the ultrasonic ranging module and the obstacle: s=vt/2.
The HC-SR04 ultrasonic ranging module integrates both an ultrasonic transmitter and a receiver. The
transmitter is used to convert electrical signals (electrical energy) into high frequency (beyond human hearing)
sound waves (mechanical energy) and the function of the receiver is opposite of this. The picture and the
diagram of the HC SR04 ultrasonic ranging module are shown below:
Technical specs:
Working voltage: 5V Working current: 12mA
Minimum measured distance: 2cm Maximum measured distance: 200cm
Instructions for use: output a high-level pulse in Trig pin lasting for least 10us, the module begins to transmit
ultrasonic waves. At the same time, the Echo pin is pulled up. When the module receives the returned
ultrasonic waves from encountering an obstacle, the Echo pin will be pulled down. The duration of high level
in the Echo pin is the total time of the ultrasonic wave from transmitting to receiving, s=vt/2.
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