File content as of revision 0:c587e0d5adda:

// HCSR04 ultrasonic sensor class using interrupts and allowing multiple instances.
// You can use the same trigger pin for multiple instances, the echo is recieved and 
// measurement calculated based on the echo input alone (when the echo signal goes high
// the timer is started, when the echo signal is low the timer value in microseconds
// is saved as the length, and the timer is stopped and reset.  Length calculation is done
// when the length is requested (either inches or centimeters) using the appropriate
// function. 
//

#ifndef MBED_HCSR04_H
#define MBED_HCSR04_H

//required to use mbed functions
#include "mbed.h"

#define TRIGGER_DELAY       12      // length of trigger signal expected by HCSR04 sensor
#define INCHES_DIVISOR      148     // 
#define CM_DIVISOR          58

class hcsr04 {

private:
    InterruptIn *_echo_int;						// pin to receive echo signal
	DigitalOut trigger_out;					// pin to send the trigger signal
	Timer timer;							// timer to track length of pulse
	// int timestart;							// beginning time of echo pulse
    float value;				            // to store the last pulse length		

public:
    bool measuring;                         // true while the echo signal is high (measurement in progress)
    hcsr04(PinName trigger, PinName echo) : trigger_out(trigger) { // _pass the names to the pin configuration                              					 
       // _trigger_out = new DigitalOut( trigger );
        _echo_int = new InterruptIn( echo );
        _echo_int->rise(this, &hcsr04::timer_start);
        _echo_int->fall(this, &hcsr04::calc_measurement);
        measuring = false;
    }



void calc_measurement() {
    value = timer.read_us();
	//value = timer.read_us() - timestart;
	timer.stop();
	timer.reset();
	measuring = false;
}
	
void timer_start() {
	this->timer.start();
	measuring = true;
}
	
void trigger(void) {
	trigger_out.write(1);                  	// start trigger signal
    wait_us(TRIGGER_DELAY); 
    trigger_out.write(0);	                // end trigger signal
}
	
float inches() {
    return value / INCHES_DIVISOR;
}
	
float cm() {
	return value /CM_DIVISOR;
}
	
};

#endif