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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. 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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3.2 HCSR04 library function description
Long timing()
Function name: timing
Parameters: None
Return Value: the time of ultrasonic from the transmitter to the receiver
float CalcDistance(long microsec,int metric)
Function name:CalcDistance
� microsec: the time of ultrasonic from the transmitter to the receiver
� metric: Set the unit of the return value ( the value of 1 for cm, and the value
of 0 for in )
Return Value: the measured distance
3.3 Add the HC-SR04 Library
Step1:Download the Demo Code of HCSR04 Ultrasonic from address
http://www.elecfreaks.com/store/download/product/Sensor/HC-SR04/HCSR04Ultrasonic_demo.zip and
then unpack it to get the file of HCSR04 Ultrasonic.
Step2: Add the file of HCSR04 Ultrasonic in the file of Arduino-1.0.X / libraries.
Step3:If you can see the Example of HCSR04 Ultrasonic in Arduino IDE, the
adding of HC-SR04 library has been successful.
3.4 Test the Module with the Examples of Library File
1. Open Arduino IDE 1.0.X, and choose the corresponding board and
serial port.
2. Click file/ examples/ HCSR04Ultrasonic until the code pop up.
3. Compiling sketch until Done uploading appears, which represents the
uploading has been successful.
4. Open serial monitor and set the corresponding BaudRate.
5. If you see similar information in serial monitor as below, you succeeded.
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