HC-SR04 User Guide Part 1 Ultrasonic Introduction 1.
1 Ultrasonic Definition The human ear can hear sound frequency around 20HZ ~ 20KHZ, and ultrasonic is the sound wave beyond the human ability of 20KHZ .
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2 Ultrasonic distance measurement principle Ultrasonic transmitter emitted an ultrasonic wave in one direction, and started timing when it launched.
Ultrasonic spread in the air, and would return immediately when it encountered obstacles on the way.
At last, the ultrasonic receiver would stop timing when it received the reflected wave.
As Ultrasonic spread velocity is 340m / s in the air, based on the timer record t, we can calculate the distance (s) between the obstacle and transmitter,...

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