hcsr04.h

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