Ultrasound Ranging Sensor module

Dependents:   Obstacle_avoidance servourfmatlab hcsr04 DistanceOnSevenSegLed ... more


The HC-SR04 ultrasonic sensor uses sonar to determine distance to an object like bats or dolphins do. It offers excellent range accuracy and stable readings in an easy-to-use package. It operation is not affected by sunlight or black material like Sharp rangefinders are (although acoustically soft materials like cloth can be difficult to detect).

Sensor (HCSR04) Details

You can find the details of the sensor at http://www.micropik.com/PDF/HCSR04.pdf /media/uploads/prabhuvd/_scaled_hcsr04.png

Working principle

The trigger input is sent a 10 usec pulse and followed by that the pulse width on the echo line is measured , the measured pulse width is then converted into distance in cm.



Calculation : The sonic speed is 343 m/sec , when converted to cm/usec , it will 343 * 100/ 1000000 = 343 /10000 cm/usec The width of the pulse is equivalent to time taken by ultrasonic wave to reach obstacle and bounce back , hence the distance of the object will be half the pulse width.

Distance (cm) = measured pulse width * 343/20000 cm.




include the mbed library with this snippet

#include "mbed.h"
#include "hcsr04.h"
#include "TextLCD.h"

DigitalOut myled(LED1);
HCSR04  usensor(p25,p6);
TextLCD lcd(p14, p16, p17, p18, p19, p20,TextLCD::LCD16x2); // rs, e, d4-d7
unsigned int dist;
int main()
    while(1) {
        lcd.printf("cm:%ld",dist );

--- a/hcsr04.h	Sat Mar 30 18:52:13 2013 +0000
+++ b/hcsr04.h	Sat Mar 30 18:55:03 2013 +0000
@@ -26,7 +26,7 @@
 #include "mbed.h"
-/** Distance Measure Class(es)
+/** HCSR04 Class(es)
 class HCSR04
@@ -43,11 +43,11 @@
     unsigned int get_dist_cm(void);
     /** Return the pulse duration equal to sonic waves travelling to obstacle and back to receiver.
-    * @param pulse duration in microseconds. 
-    */    
+    * @param pulse duration in microseconds.
+    */
     unsigned int get_pulse_us(void);
     /** Generates the trigger pulse of 10us on the trigger PIN.
-    */      
+    */
     void start(void );
     void isr_rise(void);
     void isr_fall(void);