HMC5883.cpp

00001 #include "HMC5883.h"
00002 
00003 HMC5883::HMC5883(PinName sda, PinName scl) : I2C_Sensor(sda, scl, HMC5883_I2C_ADDRESS)
00004 {   
00005     // load calibration values
00006     //loadCalibrationValues(scale, 3, "COMPASS_SCALE.txt");
00007     //loadCalibrationValues(offset, 3, "COMPASS_OFFSET.txt");
00008     
00009     // initialize HMC5883
00010     writeRegister(HMC5883_CONF_REG_A, 0x78);                // 8 samples, 75Hz output, normal mode
00011     //writeRegister(HMC5883_CONF_REG_A, 0x19);              // 8 samples, 75Hz output, test mode! (should get constant values from measurement, see datasheet)
00012     writeRegister(HMC5883_CONF_REG_B, 0x20);                // Gain for +- 1.3 gauss (earth compass ~0.6 gauss)
00013     writeRegister(HMC5883_MODE_REG, 0x00);                  // continuous measurement-mode
00014 }
00015 
00016 void HMC5883::read()
00017 {
00018     readraw();
00019     for(int i = 0; i < 3; i++)
00020         data[i] = scale[i] * (float)(raw[i]) + offset[i];
00021 }
00022 
00023 void HMC5883::calibrate(int s)
00024 {
00025     int Min[3];                                             // values for achieved maximum and minimum amplitude in calibrating environment
00026     int Max[3];
00027     
00028     Timer calibrate_timer;                                  // timer to know when calibration is finished
00029     calibrate_timer.start();
00030     
00031     while(calibrate_timer.read() < s)                       // take measurements for s seconds
00032     {
00033         readraw();
00034         for(int i = 0; i < 3; i++) {
00035             Min[i] = Min[i] < raw[i] ? Min[i] : raw[i];      // after each measurement check if there's a new minimum or maximum
00036             Max[i] = Max[i] > raw[i] ? Max[i] : raw[i];
00037         }
00038     }
00039     
00040     for(int i = 0; i < 3; i++) {
00041         scale[i]= 2000 / (float)(Max[i]-Min[i]);            // calculate scale and offset out of the measured maxima and minima
00042         offset[i]= 1000 - (float)(Max[i]) * scale[i];       // the lower bound is -1000, the higher one 1000
00043     }
00044     
00045     saveCalibrationValues(scale, 3, "COMPASS_SCALE.txt");   // save new scale and offset values to flash
00046     saveCalibrationValues(offset, 3, "COMPASS_OFFSET.txt");
00047 }
00048 
00049 void HMC5883::readraw()
00050 {
00051     char buffer[6];                                         // 8-Bit pieces of axis data
00052     
00053     readMultiRegister(HMC5883_DATA_OUT_X_MSB, buffer, 6);   // read axis registers using I2C
00054     
00055     raw[0] = (short) (buffer[0] << 8 | buffer[1]);          // join 8-Bit pieces to 16-bit short integers
00056     raw[1] = (short) (buffer[4] << 8 | buffer[5]);          // X, Z and Y (yes, order is stupid like this, see datasheet)
00057     raw[2] = (short) (buffer[2] << 8 | buffer[3]);
00058 }
00059 
00060 float HMC5883::get_angle()
00061 {
00062     #define RAD2DEG     57.295779513082320876798154814105
00063 
00064     float Heading;
00065     
00066     Heading = RAD2DEG * atan2(data[0],data[1]);
00067     Heading += 1.367;                   // correction of the angle between geographical and magnetical north direction, called declination
00068                                         // if you need an east-declination += DecAngle, if you need west-declination -= DecAngle
00069                                         // for me in Switzerland, Bern it's ca. 1.367 degree east
00070                                         // see:     http://magnetic-declination.com/
00071                                         // for me:  http://www.swisstopo.admin.ch/internet/swisstopo/de/home/apps/calc/declination.html
00072     if(Heading < 0)  
00073         Heading += 360;                 // minimum 0 degree
00074         
00075     if(Heading > 360)   
00076         Heading -= 360;                 // maximum 360 degree
00077 
00078     return Heading;
00079 }
00080     
00081