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. 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, namely: s =

340t / 2, which is so- called time difference distance measurement principle

The principle of ultrasonic distance measurement used the already-known air

spreading velocity, measuring the time from launch to reflection when it

encountered obstacle, and then calculate the distance between the transmitter

and the obstacle according to the time and the velocity. Thus, the principle of

ultrasonic distance measurement is the same with radar.

Distance Measurement formula is expressed as: L = C X T

In the formula, L is the measured distance, and C is the ultrasonic spreading

velocity in air, also, T represents time (T is half the time value from transmitting

to receiving ).

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