IMU.cpp

00001 /**
00002  * @author Eric Van den Bulck
00003  *
00004  * @section LICENSE
00005  *
00006  * Copyright (c) 2010 ARM Limited
00007  *
00008  * @section DESCRIPTION
00009  *
00010  * Pololu MinIMU-9 v2 sensor:
00011  *   L3GD20 three-axis digital output gyroscope.
00012  *   LSM303 three-axis digital accelerometer and magnetometer 
00013  *
00014  * Information to build this library:
00015  * 1. The Arduino libraries for this sensor from the Pololu and Adafruit websites, available at gitbub.
00016  *       https://github.com/adafruit/Adafruit_L3GD20
00017  *       https://github.com/pololu/L3G/tree/master/L3G
00018  * 2. The Rasberry Pi code at https://github.com/idavidstory/goPiCopter/tree/master/io/sensors
00019  *       https://github.com/idavidstory/goPiCopter/tree/master/io/sensors
00020  * 3. Information on how to write libraries:  http://mbed.org/cookbook/Writing-a-Library
00021  * 4. Information on I2C control: http://mbed.org/users/mbed_official/code/mbed/
00022  * 5. The Youtube videos from Brian Douglas (3 x 15') at http://www.youtube.com/playlist?list=PLUMWjy5jgHK30fkGrufluENJqZmLZkmqI
00023  * http://www.x-io.co.uk/open-source-imu-and-ahrs-algorithms/
00024  * Reading an IMU Without Kalman: The Complementary Filter:  http://www.pieter-jan.com/node/11
00025  * setup info on the minIMU-9 v2 on http://forum.pololu.com/viewtopic.php?f=3&t=4801&start=30
00026  */
00027 
00028 #include "mbed.h"
00029 #include "IMU.h"
00030 
00031 IMU::IMU(PinName sda, PinName scl) : _i2c(sda, scl) {
00032     _i2c.frequency(400000);  /* 400kHz, fast mode. */
00033 }
00034 
00035 char IMU::init(void)  /* returns error upon a non-zero return */
00036 {
00037    char ack, rx, tx[2];
00038    double pi, a, A;
00039 
00040 // 1. Initialize selected registers: 2c.read and i2c.write return 0 on success (ack)
00041 // --------------------------------
00042 //
00043 // 1.a Enable L3DG20 gyrosensor and set operational mode:
00044 // CTRL_REG1: set to 0x1F = 0001-1111 --> enable sensor, DR= 95Hz, LPF-Cut-off-freq=25Hz.
00045 // CTRL_REG1: set to 0x5F = 0101-1111 --> enable sensor, DR=190Hz, LPF-Cut-off-freq=25Hz.
00046 // CTRL_REG4: left at default = 0x00 --> Full Scale = 250 degrees/second --> Sensitivity = 0.00875 dps/digit.
00047     address = L3GD20_ADDR;
00048     tx[0] = L3GD20_CTRL_REG1; // address contrl_register 1
00049     tx[1] = 0x1F; // 00-01-1-111 enable sensor and set operational mode. 
00050     ack = _i2c.write(address, tx, 2);
00051     ack |= _i2c.write(address, tx, 1);
00052     ack |= _i2c.read(address+1, &rx, 1); if (rx != 0x1F) ack |= 1;
00053 //
00054 // 1.b Enable LSM303 accelerometer and set operational mode:
00055 // CTRL_REG1: set to 0x37 = 0011 0111 --> DR =  25Hz & enable sensor
00056 // CTRL_REG1: set to 0x47 = 0100 0111 --> DR =  50Hz & enable sensor
00057 // CTRL_REG1: set to 0x57 = 0101 0111 --> DR = 100Hz & enable sensor
00058 // CTRL_REG1: set to 0x77 = 0111 0111 --> DR = 200Hz & enable sensor
00059 // CTRL_REG4: set to 0x08 = 0000 1000 --> Full Scale = +/- 2G & high resolution --> Sensitivity = 0.001G/digit.
00060     address = LSM303_A_ADDR; 
00061     tx[0] = LSM303_A_CTRL_REG1;
00062     tx[1] = 0x57; //                    --> 200 Hz Data rate speed - p.24/42 of datasheet
00063     ack |= _i2c.write(address, tx, 2);
00064     ack |= _i2c.write(address, tx, 1);
00065     ack |= _i2c.read(address+1, &rx, 1); if (rx != 0x57) ack |= 1;    
00066     tx[0] = LSM303_A_CTRL_REG4;
00067     tx[1] = 0x08; // 0000 1000 enable high resolution mode + selects default 2G scale. p.26/42
00068     ack |= _i2c.write(address, tx ,2);
00069     ack |= _i2c.write(address, tx, 1);
00070     ack |= _i2c.read(address+1, &rx, 1); if (rx != 0x08) ack |= 1;    
00071 //
00072 // 1.c enable LSM303 magnetometer and set operational mode:
00073 // CRA_REG is reset from 0x10 to 0x14 = 00010100 -->  30 Hz data output rate.
00074 // CRA_REG is reset from 0x10 to 0x18 = 00011000 -->  75 Hz data output rate.
00075 // CRA_REG is reset from 0x10 to 0x1C = 00011100 --> 220 Hz data output rate.
00076 // CRB_REG is kept at default = 00100000 = 0x20 --> range +/- 1.3 Gauss, Gain = 1100/980(Z) LSB/Gauss.
00077 // MR_REG is reset from 0x03 to 0x00 -> continuos conversion mode in stead of sleep mode.
00078     address = LSM303_M_ADDR; 
00079     tx[0] = LSM303_M_CRA_REG;
00080     tx[1] = 0x18;                       //  -->  75 Hz minimum output rate - p.36/42 of datasheet
00081     ack |= _i2c.write(address, tx, 2);
00082     ack |= _i2c.write(address, tx, 1);
00083     ack |= _i2c.read(address+1, &rx, 1); if (rx != 0x18) ack |= 1;    
00084     tx[0] = LSM303_M_MR_REG;
00085     tx[1] = 0x00; // 0000 0000 --> continuous-conversion mode 25 Hz Data rate speed - p.24/42 of datasheet
00086     ack |= _i2c.write(address, tx, 2);
00087     ack |= _i2c.write(address, tx, 1);
00088     ack |= _i2c.read(address+1, &rx, 1); if (rx != 0x00) ack |= 1;    
00089  
00090 // 2. Initialize calibration constants with predetermined values.
00091 // acceleration:
00092 // My calibration values, vs. the website http://rwsarduino.blogspot.be/2013/01/inertial-orientation-sensing.html
00093 
00094 /* my predetermined static bias counts */
00095     L3GD20_biasX = (int16_t)   90;  /* digit counts */
00096     L3GD20_biasY = (int16_t) -182;
00097     L3GD20_biasZ = (int16_t)  -10;
00098 
00099 /* reference gravity acceleration */
00100     g_0 = 9.815;
00101 
00102 /* filter parameters: assume 50 Hz sampling rare and 2nd orcer Butterworth filter with fc = 6Hz. */
00103     pi = 3.1415926536;     
00104     A = tan(pi*6/50); a = 1 + sqrt(2.0)*A + A*A;
00105     FF[1] = 2*(A*A-1)/a;
00106     FF[2] = (1-sqrt(2.0)*A+A*A)/a;
00107     FF[0] = (1+FF[1]+FF[2])/4;
00108 
00109     return ack;
00110 }
00111 
00112 char IMU::readData(float *d) 
00113 {
00114       char ack, reg, D[6];
00115       int16_t W[3];
00116 
00117 // report the data in rad/s
00118 // gyro data are 16 bit readings per axis, stored: X_l, X_h, Y_l, Y_h, Z_l, Z_h
00119 // #define L3GD20_SENSITIVITY_250DPS 0.00875  ---  #define L3GD20_DPS_TO_RADS  0.017453293
00120          address = L3GD20_ADDR;
00121          reg = L3GD20_OUT_X_L | 0x80; // set address auto-increment bit
00122          ack = _i2c.write(address,&reg,1);  ack |= _i2c.read(address+1,D,6); 
00123          W[0] = (int16_t) (D[1] << 8 | D[0]); 
00124          W[1] = (int16_t) (D[3] << 8 | D[2]); 
00125          W[2] = (int16_t) (D[5] << 8 | D[4]); 
00126          *(d+0) = (float) 0.971*(W[0]-L3GD20_biasX)*L3GD20_SENSITIVITY_250DPS*L3GD20_DPS_TO_RADS;
00127          *(d+1) = (float) 0.998*(W[1]-L3GD20_biasY)*L3GD20_SENSITIVITY_250DPS*L3GD20_DPS_TO_RADS;
00128          *(d+2) = (float) 1.002*(W[2]-L3GD20_biasZ)*L3GD20_SENSITIVITY_250DPS*L3GD20_DPS_TO_RADS;
00129          
00130 // Accelerometer data are stored as 12 bit readings, left justified per axis.
00131 // The data needs to be shifted 4 digits to the right! This is not general, only for the A measurement.
00132          address = LSM303_A_ADDR; 
00133          reg = LSM303_A_OUT_X_L | 0x80; // set address auto-increment bit
00134          ack |= _i2c.write(address,&reg,1);  ack |= _i2c.read(address+1,D,6); 
00135          W[0] = ((int16_t) (D[1] << 8 | D[0])) >> 4;
00136          W[1] = ((int16_t) (D[3] << 8 | D[2])) >> 4;
00137          W[2] = ((int16_t) (D[5] << 8 | D[4])) >> 4;
00138          *(d+3) = (float) g_0*0.991*(W[0]+34)/1000; 
00139          *(d+4) = (float) g_0*0.970*(W[1]+2)/1000; 
00140          *(d+5) = (float) g_0*0.983*(W[2]+28)/1000;  
00141 // GN = 001  
00142 // Magnetometer; are stored as 12 bit readings, right justified per axis.
00143          address = LSM303_M_ADDR; 
00144          reg = LSM303_M_OUT_X_H | 0x80; // set address auto-increment bit
00145          ack |= _i2c.write(address,&reg,1);  ack |= _i2c.read(address+1,D,6); 
00146          W[0] = ((int16_t) (D[0] << 8 | D[1]));
00147          W[1] = ((int16_t) (D[4] << 8 | D[5]));
00148          W[2] = ((int16_t) (D[2] << 8 | D[3]));
00149          *(d+6) = (float) 2.813*(W[0]-264)/1100; 
00150          *(d+7) = (float) 2.822*(W[1]- 98)/1100; 
00151          *(d+8) = (float) 2.880*(W[2]-305)/980; 
00152 
00153          return ack;
00154 }
00155 
00156 void IMU::filterData(float *d, double *D) 
00157 // 2nd order Butterworth filter. Filter coefficients FF computed in function init.
00158 {
00159     for (int i=0; i<9; ++i) {
00160 //        *(FD+9*i+2) = *(FD+9*i+1); *(FD+9*i+1) = *(FD+9*i); *(FD+9*i) = (double) d[i];
00161          FD[2][i] = FD[1][i]; FD[1][i] = FD[0][i]; FD[0][i] = (double) d[i];
00162          FD[5][i] = FD[4][i]; FD[4][i] = FD[3][i]; 
00163          FD[3][i] = FF[0]*(FD[0][i] + 2*FD[1][i] + FD[2][i]) - FF[1]*FD[4][i] - FF[2]*FD[5][i];
00164          D[i] = FD[3][i]; 
00165     }
00166 //         D[0] = FD[0][2]; D[1] = FD[1][2]; D[2] = FD[2][2];
00167 }