MBED Example: How to use STMicro LSM303DLH 3 axis magnetometer with 3 axis accelerometer.

.from: http://mbed.org/users/shimniok/libraries/LSM303DLH/lpk7s5

XxXxXxXxXxXxXxXxXxXxXxXxXxXx LSM303DLH.cpp XxXxXxXxXxXxXxXxXxXxXxXxXxXx

/** LSM303DLH Interface Library
 *
 * Michael Shimniok http://bot-thoughts.com
 *
 * Based on test program by @tosihisa and
 *
 * Pololu sample library for LSM303DLH breakout by ryantm:
 *
 * Copyright (c) 2011 Pololu Corporation. For more information, see
 *
 * http://www.pololu.com/
 * http://forum.pololu.com/
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */
#include "mbed.h"
#include "LSM303DLH.h"

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

#define FILTER_SHIFT 6      // used in filtering acceleromter readings

const int addr_acc = 0x30;
const int addr_mag = 0x3c;

enum REG_ADDRS {
    /* --- Mag --- */
    CRA_REG_M   = 0x00,
    CRB_REG_M   = 0x01,
    MR_REG_M    = 0x02,
    OUT_X_M     = 0x03,
    OUT_Y_M     = 0x05,
    OUT_Z_M     = 0x07,
    /* --- Acc --- */
    CTRL_REG1_A = 0x20,
    CTRL_REG4_A = 0x23,
    OUT_X_A     = 0x28,
    OUT_Y_A     = 0x2A,
    OUT_Z_A     = 0x2C,
};

bool LSM303DLH::write_reg(int addr_i2c,int addr_reg, char v)
{
    char data[2] = {addr_reg, v};
    return LSM303DLH::_compass.write(addr_i2c, data, 2) == 0;
}

bool LSM303DLH::read_reg(int addr_i2c,int addr_reg, char *v)
{
    char data = addr_reg;
    bool result = false;
   
    __disable_irq();
    if ((_compass.write(addr_i2c, &data, 1) == 0) && (_compass.read(addr_i2c, &data, 1) == 0)){
        *v = data;
        result = true;
    }
    __enable_irq();
    return result;
}

bool LSM303DLH::read_reg_short(int addr_i2c,int addr_reg, short *v)
{
    char *pv = (char *)v;
    bool result;
   
    result =  read_reg(addr_i2c,addr_reg+0,pv+1);
    result &= read_reg(addr_i2c,addr_reg+1,pv+0);
 
    return result;
}

LSM303DLH::LSM303DLH(PinName sda, PinName scl):
    _compass(sda, scl), _offset_x(0), _offset_y(0), _offset_z(0), _scale_x(0), _scale_y(0), _scale_z(0), _filt_ax(0), _filt_ay(0), _filt_az(6000)
{
    char reg_v;
    _compass.frequency(100000);
       
    reg_v = 0;
    reg_v |= 0x01 << 5;     /* Normal mode  */
    reg_v |= 0x07;          /* X/Y/Z axis enable. */
    write_reg(addr_acc,CTRL_REG1_A,reg_v);
    reg_v = 0;
    read_reg(addr_acc,CTRL_REG1_A,&reg_v);

    reg_v = 0;
    reg_v |= 0x01 << 6;     /* 1: data MSB @ lower address */
    reg_v |= 0x01 << 4;     /* +/- 4g */
    write_reg(addr_acc,CTRL_REG4_A,reg_v);

    /* -- mag --- */
    reg_v = 0;
    reg_v |= 0x04 << 2;     /* Minimum data output rate = 15Hz */
    write_reg(addr_mag,CRA_REG_M,reg_v);

    reg_v = 0;
    //reg_v |= 0x01 << 5;     /* +-1.3Gauss */
    reg_v |= 0x07 << 5;     /* +-8.1Gauss */
    write_reg(addr_mag,CRB_REG_M,reg_v);

    reg_v = 0;              /* Continuous-conversion mode */
    write_reg(addr_mag,MR_REG_M,reg_v);
}


void LSM303DLH::setOffset(float x, float y, float z)
{
    _offset_x = x;
    _offset_y = y;
    _offset_z = z;  
}

void LSM303DLH::setScale(float x, float y, float z)
{
    _scale_x = x;
    _scale_y = y;
    _scale_z = z;
}

void LSM303DLH::read(vector &a, vector &m)
{
    short a_x, a_y, a_z;
    short m_x, m_y, m_z;
    //Timer t;
    //int usec1, usec2;
   
    //t.reset();
    //t.start();

    //usec1 = t.read_us();
    read_reg_short(addr_acc, OUT_X_A, &a_x);
    read_reg_short(addr_acc, OUT_Y_A, &a_y);
    read_reg_short(addr_acc, OUT_Z_A, &a_z);
    read_reg_short(addr_mag, OUT_X_M, &m_x);
    read_reg_short(addr_mag, OUT_Y_M, &m_y);
    read_reg_short(addr_mag, OUT_Z_M, &m_z);
    //usec2 = t.read_us();
   
    //if (debug) debug->printf("%d %d %d\n", usec1, usec2, usec2-usec1);

    // Perform simple lowpass filtering
    // Intended to stabilize heading despite
    // device vibration such as on a UGV
    _filt_ax += a_x - (_filt_ax >> FILTER_SHIFT);
    _filt_ay += a_y - (_filt_ay >> FILTER_SHIFT);
    _filt_az += a_z - (_filt_az >> FILTER_SHIFT);

    a.x = (float) (_filt_ax >> FILTER_SHIFT);
    a.y = (float) (_filt_ay >> FILTER_SHIFT);
    a.z = (float) (_filt_az >> FILTER_SHIFT);
   
    // offset and scale
    m.x = (m_x + _offset_x) * _scale_x;
    m.y = (m_y + _offset_y) * _scale_y;
    m.z = (m_z + _offset_z) * _scale_z;
}


// Returns the number of degrees from the -Y axis that it
// is pointing.
float LSM303DLH::heading()
{
    return heading((vector){0,-1,0});
}

float LSM303DLH::heading(vector from)
{
    vector a, m;

    this->read(a, m);
   
    ////////////////////////////////////////////////
    // compute heading      
    ////////////////////////////////////////////////

    vector temp_a = a;
    // normalize
    vector_normalize(&temp_a);
    //vector_normalize(&m);

    // compute E and N
    vector E;
    vector N;
    vector_cross(&m,&temp_a,&E);
    vector_normalize(&E);
    vector_cross(&temp_a,&E,&N);
   
    // compute heading
    float heading = atan2(vector_dot(&E,&from), vector_dot(&N,&from)) * 180/M_PI;
    if (heading < 0) heading += 360;
   
    return heading;
}

void LSM303DLH::frequency(int hz)
{
    _compass.frequency(hz);
}

XxXxXxXxXxXxXxXxXxXxXxXxXxXx LSM303DLH.h XxXxXxXxXxXxXxXxXxXxXxXxXxXx

#include "mbed.h"
#include "vector.h"

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

/** Tilt-compensated compass interface Library for the STMicro LSM303DLH 3-axis magnetometer, 3-axis acceleromter
 *
 * Michael Shimniok http://bot-thoughts.com
 *
 * Based on test program by @tosihisa and
 *
 * Pololu sample library for LSM303DLH breakout by ryantm:
 *
 * Copyright (c) 2011 Pololu Corporation. For more information, see
 *
 * http://www.pololu.com/
 * http://forum.pololu.com/
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * @code
 * #include "mbed.h"
 * #include "LSM303DLH.h"
 *
 * Serial debug(USBTX,USBRX);
 * LSM303DLH compass(p28, p27);
 *
 * int main() {
 *   float hdg;
 *   debug.format(8,Serial::None,1);
 *   debug.baud(115200);
 *   debug.printf("LSM303DLH Test\x0d\x0a");
 *   compass.setOffset(29.50, -0.50, 4.00); // example calibration
 *   compass.setScale(1.00, 1.03, 1.21);    // example calibration
 *   while(1) {
 *     hdg = compass.heading();
 *     debug.printf("Heading: %.2f\n", hdg);
 *     wait(0.1);
 *   }
 * }
 * @endcode
 */
class LSM303DLH {
    public:
        /** Create a new interface for an LSM303DLH
         *
         * @param sda is the pin for the I2C SDA line
         * @param scl is the pin for the I2C SCL line
         */
        LSM303DLH(PinName sda, PinName scl);

        /** sets the x, y, and z offset corrections for hard iron calibration
         *
         * Calibration details here:
         *  http://mbed.org/users/shimniok/notebook/quick-and-dirty-3d-compass-calibration/
         *
         * If you gather raw magnetometer data and find, for example, x is offset
         * by hard iron by -20 then pass +20 to this member function to correct
         * for hard iron.
         *
         * @param x is the offset correction for the x axis
         * @param y is the offset correction for the y axis
         * @param z is the offset correction for the z axis
         */
        void setOffset(float x, float y, float z);
       
        /** sets the scale factor for the x, y, and z axes
         *
         * Calibratio details here:
         *  http://mbed.org/users/shimniok/notebook/quick-and-dirty-3d-compass-calibration/
         *
         * Sensitivity of the three axes is never perfectly identical and this
         * function can help to correct differences in sensitivity.  You're
         * supplying a multipler such that x, y and z will be normalized to the
         * same max/min values
         */
        void setScale(float x, float y, float z);

        /** read the raw accelerometer and compass values
         *
         * @param a is the accelerometer 3d vector, written by the function
         * @param m is the magnetometer 3d vector, written by the function
         */
        void read(vector &a, vector &m);
       
        /** returns the magnetic heading with respect to the y axis
         *
         */
        float heading(void);
       
        /** returns the heading with respect to the specified vector
         *
         */
        float heading(vector from);
   
        /** sets the I2C bus frequency
         *
         * @param frequency is the I2C bus/clock frequency, either standard (100000) or fast (400000)
         */
        void frequency(int hz);
   
    private:
        I2C _compass;
        float _offset_x;
        float _offset_y;
        float _offset_z;
        float _scale_x;
        float _scale_y;
        float _scale_z;
        long _filt_ax;
        long _filt_ay;
        long _filt_az;
      
        bool write_reg(int addr_i2c,int addr_reg, char v);
        bool read_reg(int addr_i2c,int addr_reg, char *v);
        bool read_reg_short(int addr_i2c,int addr_reg, short *v);
};
 

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 #include <vector.h>
#include <math.h>

void vector_cross(const vector *a,const vector *b, vector *out)
{
  out->x = a->y*b->z - a->z*b->y;
  out->y = a->z*b->x - a->x*b->z;
  out->z = a->x*b->y - a->y*b->x;
}

float vector_dot(const vector *a,const vector *b)
{
  return a->x*b->x+a->y*b->y+a->z*b->z;
}

void vector_normalize(vector *a)
{
  float mag = sqrt(vector_dot(a,a));
  a->x /= mag;
  a->y /= mag;
  a->z /= mag;
}

XxXxXxXxXxXxXxXxXxXxXxXxXxXx vector.h XxXxXxXxXxXxXxXxXxXxXxXxXxXx

 #ifndef vector_h
#define vector_h
typedef struct vector
{
  float x, y, z;
} vector;

extern void vector_cross(const vector *a, const vector *b, vector *out);
extern float vector_dot(const vector *a,const vector *b);
extern void vector_normalize(vector *a);
#endif

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