HCSR04.cpp

00001 /* File: HCSR04.h
00002  * Author: Robert Abad  Copyright (c) 2013
00003  *
00004  * Desc: driver for HCSR04 Ultrasonic Range Finder.  See header file,
00005  *       HCSR04.h, for more details.
00006  */
00007 
00008 #include "mbed.h"
00009 #include "HCSR04.h"
00010 
00011 #define SPEED_OF_SOUND      (343.2f)    // meters/sec
00012 
00013 // HCSR04 TRIGGER pin
00014 #define SIGNAL_HIGH     (1)
00015 #define SIGNAL_LOW      (0)
00016 
00017 #define TRIGGER_TIME    (10)            // microseconds
00018 
00019 
00020 // Name: HCSR04
00021 // Desc: HCSR04 constructor
00022 // Inputs: PinName - pin used for trigger signal
00023 //         PinName - pin used for echo signal
00024 // Outputs: none
00025 //
00026 HCSR04::HCSR04( PinName pinTrigger, PinName pinEcho ) : 
00027 trigger(pinTrigger),
00028 echo(pinEcho),
00029 measTimeStart_us(0),
00030 measTimeStop_us(0)
00031 {
00032     echo.rise( this, &HCSR04::ISR_echoRising );
00033     echo.fall( this, &HCSR04::ISR_echoFalling );
00034     echoTimer.start();
00035 }
00036 
00037 // Name: startMeas
00038 // Desc: initiates range measurement driving the trigger signal HIGH then sets
00039 //       a timer to keep trigger HIGH for the duration of TRIGGER_TIME
00040 // Inputs: none
00041 // Outputs: none
00042 //
00043 void HCSR04::startMeas(void)
00044 {
00045     trigger = SIGNAL_HIGH;
00046     echoTimer.reset();
00047     triggerTicker.attach_us(this, &HCSR04::triggerTicker_cb, TRIGGER_TIME);
00048 }
00049  
00050 // Name: getMeas
00051 // Desc: returns range measurement in meters
00052 // Inputs: float & - reference to range measurement
00053 // Outputs: etHCSR04 - RANGE_MEAS_VALID or RANGE_MEAS_INVALID
00054 //
00055 etHCSR04_RANGE_STATUS HCSR04::getMeas(float &rRangeMeters)
00056 {
00057     unsigned long dTime_us;
00058     if ( !measTimeStart_us || !measTimeStop_us )
00059     {
00060         return RANGE_MEAS_INVALID;
00061     }
00062     
00063     dTime_us = measTimeStop_us - measTimeStart_us;
00064     rRangeMeters = (float)dTime_us / 1000000. * SPEED_OF_SOUND / 2;
00065     measTimeStart_us = 0;
00066     measTimeStop_us = 0;
00067     return ( RANGE_MEAS_VALID );
00068 }
00069 
00070 // Name: triggerTicker_cb
00071 // Desc: Timer ticker callback function used to drive trigger signal LOW
00072 // Inputs: none
00073 // Outputs: none
00074 //
00075 void HCSR04::triggerTicker_cb(void)
00076 {
00077     trigger = SIGNAL_LOW;
00078 }
00079 
00080 
00081 // Name: ISR_echoRising
00082 // Desc: ISR for rising edge of HCSR04 ECHO signal
00083 // Inputs: none
00084 // Outputs: none
00085 //
00086 void HCSR04::ISR_echoRising(void)
00087 {
00088     measTimeStart_us = echoTimer.read_us();
00089 }
00090 
00091 // Name: ISR_echoFalling
00092 // Desc: ISR for falling edge of HCSR04 ECHO signal
00093 // Inputs: none
00094 // Outputs: none
00095 //
00096 void HCSR04::ISR_echoFalling(void)
00097 {
00098     measTimeStop_us = echoTimer.read_us();
00099 }
00100