BMP085.cpp

00001 /*
00002  * mbed library to use a Bosch Sensortec BMP085 sensor
00003  * Copyright (c) 2010 Hiroshi Suga
00004  * Released under the MIT License: http://mbed.org/license/mit
00005  */
00006 
00007 #include "mbed.h"
00008 #include "BMP085.h"
00009 
00010 #define WEATHER_BMP085 0xee
00011 #define xpow(x, y) ((long)1 << y)
00012 const float ALTITUDE_EXPONENT = 1/5.255;
00013 const float ALTITUDE_PRESSURE_REFERENCE = 100000;
00014 const float ALTITUDE_COEFF = 44330.0;
00015 float BMP085::calcAltitude(int pressure) {
00016   //Compute an estimate of altitude
00017   // see page 15 of manual
00018   float float_comp_pressure = (float) pressure;
00019   float altitude = float_comp_pressure/ALTITUDE_PRESSURE_REFERENCE;
00020   altitude = pow(altitude, ALTITUDE_EXPONENT);
00021   altitude = 1.0 - altitude;
00022   altitude *= ALTITUDE_COEFF;
00023   // formula is: altitude = 44330 * (1-pow((p/p0), 1/5.255))
00024   return altitude;
00025 }
00026 
00027 BMP085::BMP085 (PinName p_sda, PinName p_scl, BMP085_oss p_oss) : i2c(p_sda, p_scl) {
00028     init(p_oss);
00029 }
00030 
00031 BMP085::BMP085 (I2C& p_i2c, BMP085_oss p_oss) : i2c(p_i2c) { 
00032     init(p_oss);
00033 }
00034 
00035 float BMP085::get_temperature() {
00036     return temperature;
00037 }
00038 
00039 float BMP085::get_pressure() {
00040     return pressure;
00041     
00042 }
00043 
00044 void BMP085::update () {
00045     long t, p, ut, up, x1, x2, x3, b3, b5, b6;
00046     unsigned long b4, b7;
00047 
00048     twi_writechar(WEATHER_BMP085, 0xf4, 0x2e);
00049     wait(0.01);
00050     ut = twi_readshort(WEATHER_BMP085, 0xf6);
00051 
00052     twi_writechar(WEATHER_BMP085, 0xf4, 0x34 | (oss << 6));
00053     wait(0.05);
00054     up = twi_readlong(WEATHER_BMP085, 0xf6) >> (8 - oss);
00055 
00056     x1 = (ut - ac6) * ac5 / xpow(2, 15);
00057     x2 = (long)mc * xpow(2, 11) / (x1 + md);
00058     b5 = x1 + x2;
00059     t = (b5 + 8) / xpow(2, 4);
00060     temperature = (float)t / 10.0;
00061 
00062     b6 = b5 - 4000;
00063     x1 = (b2 * (b6 * b6 / xpow(2, 12))) / xpow(2, 11);
00064     x2 = ac2 * b6 / xpow(2, 11);
00065     x3 = x1 + x2;
00066     b3 = ((((unsigned long)ac1 * 4 + x3) << oss) + 2) / 4;
00067     x1 = ac3 * b6 / xpow(2, 13);
00068     x2 = (b1 * (b6 * b6 / xpow(2, 12))) / xpow(2, 16);
00069     x3 = ((x1 + x2) + 2) / xpow(2, 2);
00070     b4 = ac4 * (unsigned long)(x3 + 32768) / xpow(2, 15);
00071     b7 = ((unsigned long)up - b3) * (50000 >> oss);
00072     if (b7 < (unsigned long)0x80000000) {
00073         p = (b7 * 2) / b4;
00074     } else {
00075         p = (b7 / b4) * 2;
00076     }
00077     x1 = (p / xpow(2, 8)) * (p / xpow(2, 8));
00078     x1 = (x1 * 3038) / xpow(2, 16);
00079     x2 = (-7357 * p) / xpow(2, 16);
00080     p = p + (x1 + x2 + 3791) / xpow(2, 4);
00081     pressure = (float)p / 100.0;
00082 }
00083 
00084 void BMP085::init (BMP085_oss p_oss) {
00085     ac1 = twi_readshort(WEATHER_BMP085, 0xaa);
00086     ac2 = twi_readshort(WEATHER_BMP085, 0xac);
00087     ac3 = twi_readshort(WEATHER_BMP085, 0xae);
00088     ac4 = twi_readshort(WEATHER_BMP085, 0xb0);
00089     ac5 = twi_readshort(WEATHER_BMP085, 0xb2);
00090     ac6 = twi_readshort(WEATHER_BMP085, 0xb4);
00091     b1 = twi_readshort(WEATHER_BMP085, 0xb6);
00092     b2 = twi_readshort(WEATHER_BMP085, 0xb8);
00093     mb = twi_readshort(WEATHER_BMP085, 0xba);
00094     mc = twi_readshort(WEATHER_BMP085, 0xbc);
00095     md = twi_readshort(WEATHER_BMP085, 0xbe);
00096     oss = p_oss;
00097 }
00098 
00099 unsigned short BMP085::twi_readshort (int id, int addr) {
00100     unsigned short i;
00101 
00102     i2c.start();
00103     i2c.write(id);
00104     i2c.write(addr);
00105 
00106     i2c.start();
00107     i2c.write(id | 1);
00108     i = i2c.read(1) << 8;
00109     i |= i2c.read(0);
00110     i2c.stop();
00111 
00112     return i;
00113 }
00114 
00115 unsigned long BMP085::twi_readlong (int id, int addr) {
00116     unsigned long i;
00117 
00118     i2c.start();
00119     i2c.write(id);
00120     i2c.write(addr);
00121 
00122     i2c.start();
00123     i2c.write(id | 1);
00124     i = i2c.read(1) << 16;
00125     i |= i2c.read(1) << 8;
00126     i |= i2c.read(0);
00127     i2c.stop();
00128 
00129     return i;
00130 }
00131 
00132 void BMP085::twi_writechar (int id, int addr, int dat) {
00133 
00134     i2c.start();
00135     i2c.write(id);
00136     i2c.write(addr);
00137     i2c.write(dat);
00138     i2c.stop();
00139 }