SRF05.cpp

00001 /* mbed SRF05 Ultrasonic Rangefiner Library
00002  * Copyright (c) 2007-2010, cstyles, sford
00003  *
00004  * Permission is hereby granted, free of charge, to any person obtaining a copy
00005  * of this software and associated documentation files (the "Software"), to deal
00006  * in the Software without restriction, including without limitation the rights
00007  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
00008  * copies of the Software, and to permit persons to whom the Software is
00009  * furnished to do so, subject to the following conditions:
00010  *
00011  * The above copyright notice and this permission notice shall be included in
00012  * all copies or substantial portions of the Software.
00013  *
00014  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
00015  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
00016  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
00017  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
00018  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
00019  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
00020  * THE SOFTWARE.
00021  */
00022 
00023 #include "SRF05.h"
00024 #include "mbed.h"
00025 
00026 SRF05::SRF05(PinName trigger, PinName echo) 
00027     : _trigger(trigger), _echo(echo) {    
00028         
00029     // Attach interrupts
00030     _echo.rise(callback(this,&SRF05::_rising));
00031     _echo.fall(callback(this,&SRF05::_falling));
00032     _ticker.attach(callback(this,&SRF05::_startRange), 0.1);
00033 }
00034   
00035 void SRF05::_startRange() {
00036     // send a trigger pulse, 20uS long
00037     _trigger = 1;
00038     //wait (0.000002);
00039     wait_us(40);
00040     _trigger = 0;
00041 }
00042 
00043 // Clear and start the timer at the begining of the echo pulse
00044 void SRF05::_rising(void) {
00045     _timer.reset();
00046     _timer.start();
00047 }
00048 
00049 // Stop and read the timer at the end of the pulse
00050 void SRF05::_falling(void) {
00051     _timer.stop();
00052     _dist = _timer.read_us()/58.0;
00053     _dist=99.0;
00054 }
00055 
00056 float SRF05::read(void) {
00057     // spin until there is a good value
00058     return (_dist);
00059 }
00060 
00061 SRF05::operator float() {
00062     return read();
00063 }