Prabhu Desai / HCSR04

Ultrasound Ranging Sensor module

Dependents:   Obstacle_avoidance servourfmatlab hcsr04 DistanceOnSevenSegLed ... more

Overview

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.

/media/uploads/prabhuvd/waveform.png

Quote:

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.

Schematic

/media/uploads/prabhuvd/schema.png

Code

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) {
        usensor.start();
        wait_ms(500); 
        dist=usensor.get_dist_cm();
        lcd.cls();
        lcd.locate(0,0);
        lcd.printf("cm:%ld",dist );
 
    }
}

Diff: hcsr04.h

Revision:
2:0acb6ade091c
Parent:
0:fb0929f37ebe
Child:
3:e6795cb9439c
diff -r 093521f56089 -r 0acb6ade091c hcsr04.h
--- a/hcsr04.h	Sat Mar 30 17:32:04 2013 +0000
+++ b/hcsr04.h	Sat Mar 30 18:41:34 2013 +0000
@@ -35,14 +35,16 @@
     /** Create a DistMeasure object connected to the specified pin
     * @param pin i/o pin to connect to
     */
-    DistMeasure(PinName TrigPin,PinName EchoPin,unsigned int maxtime);
+    DistMeasure(PinName TrigPin,PinName EchoPin);
     ~DistMeasure();
 
     /** Return the distance from obstacle in cm
     * @param distance in cms and returns -1, in case of failure
     */
  
-    unsigned int get_distance_cm(void);
+    unsigned int get_dist_cm(void);
+    unsigned int get_pulse_us(void);
+    void start_measurement(void );
     void isr_rise(void);
     void isr_fall(void);
     void fall (void (*fptr)(void));
@@ -55,7 +57,6 @@
     Timer pulsetime;
     DigitalOut  trigger;
     InterruptIn echo;
-    unsigned int timeout;
     unsigned int pulsedur;
     unsigned int distance;    
 };