hcsr04.h

00001 //  Primary Author: David Glover 
00002 //  March, 2012
00003 //  ECE 510 Embedded Systems, Roy Kravitz
00004 //
00005 // HCSR04 ultrasonic sensor class using interrupts and allowing multiple instances.
00006 // You can use the same trigger pin for multiple instances, the echo is recieved and 
00007 // measurement calculated based on the echo input alone (when the echo signal goes high
00008 // the timer is started, when the echo signal goes low the timer value in microseconds
00009 // is saved as the length, and the timer is stopped and reset.  Length calculation is done
00010 // when the length is requested (either inches or centimeters) using the appropriate
00011 // function. 
00012 
00013 #ifndef MBED_HCSR04_H
00014 #define MBED_HCSR04_H
00015 
00016 //required to use mbed functions
00017 #include "mbed.h"
00018 
00019 #define TRIGGER_DELAY       12      // length of trigger signal expected by HCSR04 sensor
00020 #define INCHES_DIVISOR      148     // 
00021 #define CM_DIVISOR          58
00022 
00023 class hcsr04 {
00024 
00025 private:
00026     InterruptIn *_echo_int;                        // pin to receive echo signal
00027     DigitalOut trigger_out;                    // pin to send the trigger signal
00028     Timer timer;                            // timer to track length of pulse
00029     float value;                            // to store the last pulse length        
00030 
00031 public:
00032     bool measuring;                         // true while the echo signal is high (measurement in progress)
00033     hcsr04(PinName trigger, PinName echo) : trigger_out(trigger) { // _pass the names to the pin configuration                                                   
00034        // _trigger_out = new DigitalOut( trigger );
00035         _echo_int = new InterruptIn( echo );
00036         _echo_int->rise(this, &hcsr04::timer_start);
00037         _echo_int->fall(this, &hcsr04::calc_measurement);
00038         measuring = false;
00039     }
00040 
00041 
00042     void calc_measurement() {
00043         value = timer.read_us();
00044         //value = timer.read_us() - timestart;
00045         timer.stop();
00046         timer.reset();
00047         measuring = false;
00048     }
00049         
00050     void timer_start() {
00051         this->timer.start();
00052         measuring = true;
00053     }
00054         
00055     void trigger(void) {
00056         trigger_out.write(1);                      // start trigger signal
00057         wait_us(TRIGGER_DELAY); 
00058         trigger_out.write(0);                    // end trigger signal
00059     }
00060         
00061     float inches() {                    // return distance in inches.
00062         return value / INCHES_DIVISOR;
00063     }
00064         
00065     float cm() {                        // return distance in centimeters.
00066         return value / CM_DIVISOR;
00067     }
00068         
00069 };
00070 
00071 #endif