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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 .
1.2 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.
HC-SR04 Datasheet
