File content as of revision 2:d99d91a7e8f1:

//  Primary Author: David Glover 
//  March, 2012
//  ECE 510 Embedded Systems, Roy Kravitz
//
// 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 goes 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
    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 distance in inches.
        return value / INCHES_DIVISOR;
    }
        
    float cm() {                        // return distance in centimeters.
        return value / CM_DIVISOR;
    }
        
};

#endif