SRF08.cpp

00001 
00002 /*
00003 Copyright (c) 2010 Chris Styles ( chris dot styles at mbed dot org )
00004 
00005 Permission is hereby granted, free of charge, to any person obtaining a copy
00006 of this software and associated documentation files (the "Software"), to deal
00007 in the Software without restriction, including without limitation the rights
00008 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
00009 copies of the Software, and to permit persons to whom the Software is
00010 furnished to do so, subject to the following conditions:
00011 
00012 The above copyright notice and this permission notice shall be included in
00013 all copies or substantial portions of the Software.
00014 
00015 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
00016 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
00017 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
00018 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
00019 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
00020 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
00021 THE SOFTWARE.
00022 */
00023 
00024 #include "SRF08.h"
00025 
00026 
00027 SRF08::SRF08(PinName sda, PinName scl, int addr) : m_i2c(sda, scl), m_addr(addr) {
00028     char cmd[2];
00029     
00030 // Set up SRF08 max range and receiver sensitivity over I2C bus
00031     cmd[0] = 0x02;                          // Range register
00032     cmd[1] = 0x1C;                          // Set max range about 100cm
00033     m_i2c.write(m_addr, cmd, 2);
00034     cmd[0] = 0x01;                          // Receiver gain register
00035     cmd[1] = 0x1B;                          // Set max receiver gain
00036     m_i2c.write(m_addr, cmd, 2);
00037 
00038 }
00039 
00040 SRF08::~SRF08 () {
00041 
00042 }
00043 
00044 float SRF08::read() {
00045 
00046     char cmd[2];
00047     char echo[2];
00048 
00049 
00050 // Get range data from SRF08
00051 // Send Tx burst command over I2C bus
00052     cmd[0] = 0x00;                      // Command register
00053     cmd[1] = 0x51;                      // Ranging results in cm
00054     m_i2c.write(m_addr, cmd, 2);          // Send ranging burst
00055 
00056     wait(0.07);                         // Wait for return echo
00057 
00058 // Read back range over I2C bus
00059     cmd[0] = 0x02;                        // Address of first echo
00060     m_i2c.write(m_addr, cmd, 1, 1);         // Send address of first echo
00061     m_i2c.read(m_addr, echo, 2);            // Read two-byte echo result
00062 
00063 // Generate PWM mark/space ratio from range data
00064     float range = (echo[0]<<8)+echo[1];
00065 
00066     return range;
00067 }