Barometer.cpp

00001 #include "mbed.h"
00002 #include "Barometer.h"
00003  
00004 #define WEATHER_Barometer 0xee
00005 #define xpow(x, y) ((long)1 << y)
00006  
00007 
00008 Barometer::Barometer (PinName p_sda, PinName p_scl, Barometer_oss p_oss) : i2c(p_sda, p_scl) {
00009     init(p_oss);
00010 }
00011  
00012 Barometer::Barometer (I2C& p_i2c, Barometer_oss p_oss) : i2c(p_i2c) { 
00013     init(p_oss);
00014 }
00015  
00016 
00017 float Barometer::get_temperature() {
00018     return temperature;
00019 }
00020  
00021 float Barometer::get_pressure() {
00022     return pressure;
00023 }
00024  
00025 float Barometer::get_altitude_m() {
00026     altitude = 44330*(1-pow((pressure/1013.25),(0.190295)));
00027     return altitude;
00028 }
00029 
00030 void Barometer::update () {
00031     long t, p, ut, up, x1, x2, x3, b3, b5, b6;
00032     unsigned long b4, b7;
00033  
00034     twi_writechar(WEATHER_Barometer, 0xf4, 0x2e);
00035     wait(0.01);
00036     ut = twi_readshort(WEATHER_Barometer, 0xf6);
00037  
00038     twi_writechar(WEATHER_Barometer, 0xf4, 0x34 | (oss << 6));
00039     wait(0.05);
00040     up = twi_readlong(WEATHER_Barometer, 0xf6) >> (8 - oss);
00041  
00042     x1 = (ut - ac6) * ac5 / xpow(2, 15);
00043     x2 = (long)mc * xpow(2, 11) / (x1 + md);
00044     b5 = x1 + x2;
00045     t = (b5 + 8) / xpow(2, 4);
00046     temperature = (float)t / 10.0;
00047  
00048     b6 = b5 - 4000;
00049     x1 = (b2 * (b6 * b6 / xpow(2, 12))) / xpow(2, 11);
00050     x2 = ac2 * b6 / xpow(2, 11);
00051     x3 = x1 + x2;
00052     b3 = ((((unsigned long)ac1 * 4 + x3) << oss) + 2) / 4;
00053     x1 = ac3 * b6 / xpow(2, 13);
00054     x2 = (b1 * (b6 * b6 / xpow(2, 12))) / xpow(2, 16);
00055     x3 = ((x1 + x2) + 2) / xpow(2, 2);
00056     b4 = ac4 * (unsigned long)(x3 + 32768) / xpow(2, 15);
00057     b7 = ((unsigned long)up - b3) * (50000 >> oss);
00058     if (b7 < (unsigned long)0x80000000) {
00059         p = (b7 * 2) / b4;
00060     } else {
00061         p = (b7 / b4) * 2;
00062     }
00063     x1 = (p / xpow(2, 8)) * (p / xpow(2, 8));
00064     x1 = (x1 * 3038) / xpow(2, 16);
00065     x2 = (-7357 * p) / xpow(2, 16);
00066     p = p + (x1 + x2 + 3791) / xpow(2, 4);
00067     pressure = (float)p / 100.0;
00068 }
00069  
00070 void Barometer::init (Barometer_oss p_oss) {
00071     ac1 = twi_readshort(WEATHER_Barometer, 0xaa);
00072     ac2 = twi_readshort(WEATHER_Barometer, 0xac);
00073     ac3 = twi_readshort(WEATHER_Barometer, 0xae);
00074     ac4 = twi_readshort(WEATHER_Barometer, 0xb0);
00075     ac5 = twi_readshort(WEATHER_Barometer, 0xb2);
00076     ac6 = twi_readshort(WEATHER_Barometer, 0xb4);
00077     b1 = twi_readshort(WEATHER_Barometer, 0xb6);
00078     b2 = twi_readshort(WEATHER_Barometer, 0xb8);
00079     mb = twi_readshort(WEATHER_Barometer, 0xba);
00080     mc = twi_readshort(WEATHER_Barometer, 0xbc);
00081     md = twi_readshort(WEATHER_Barometer, 0xbe);
00082     oss = p_oss;
00083 }
00084  
00085 unsigned short Barometer::twi_readshort (int id, int addr) {
00086     unsigned short i;
00087  
00088     i2c.start();
00089     i2c.write(id);
00090     i2c.write(addr);
00091  
00092     i2c.start();
00093     i2c.write(id | 1);
00094     i = i2c.read(1) << 8;
00095     i |= i2c.read(0);
00096     i2c.stop();
00097  
00098     return i;
00099 }
00100  
00101 unsigned long Barometer::twi_readlong (int id, int addr) {
00102     unsigned long i;
00103  
00104     i2c.start();
00105     i2c.write(id);
00106     i2c.write(addr);
00107  
00108     i2c.start();
00109     i2c.write(id | 1);
00110     i = i2c.read(1) << 16;
00111     i |= i2c.read(1) << 8;
00112     i |= i2c.read(0);
00113     i2c.stop();
00114  
00115     return i;
00116 }
00117  
00118 void Barometer::twi_writechar (int id, int addr, int dat) {
00119  
00120     i2c.start();
00121     i2c.write(id);
00122     i2c.write(addr);
00123     i2c.write(dat);
00124     i2c.stop();
00125 }