File content as of revision 1:3b2260aff305:

// MBED reference code for the ST Micro STEVAL-MKI124V1 header board
// This board has: LPS331 pressure/temperature sensor, L3GD20 gyroscope and LSM303DLHC magnetometer/accelerometer
// Code accesses each of the 3 MEMS sensors and calculates pressure, temp, heading, tilt, roll and angular velocity
// Code is not optimized for efficienecy but instead for clarity of how you use the sensors
// ST application note AN3192 was key in developing the tilt-corrected compass
// Developed on an LPC1768
// By Liam Goudge. March 2014

#define LSM303_on
#define L3GD20_on
#define LPS301_on

#include "mbed.h"
#include "MKI124V1.h"
#include "math.h"

DigitalOut myled(LED1);
Serial pc(USBTX, USBRX);    // tx, rx for USB debug printf to terminal console
I2C i2c(p28, p27);          // LPC1768 I2C pin allocation

// Globals
int16_t const   Offset_mX=-40.0;
int16_t const   Offset_mY=-115.0;
float const     RadtoDeg=(180.0/3.141592654);


char readByte(char address, char reg)
// Reads one byte from an I2C address
// Didn't bother to make a multi-byte version to read in X,Y,Z low/high series of registers because...
// the data registers of all sensors they are in the same XL,XH,YL,YH,ZL,ZH order apart from the magnetometer which is XH,XL,ZH,ZL,YH,YL...
{
    char result;
    
    i2c.start();
    i2c.write(address);         // Slave address with direction=write
    i2c.write(reg);             // Subaddress (register)
    
    i2c.start();                // Break transmission to change bus direction
    i2c.write(address + 1);     // Slave address with direction=read [bit0=1]
    
    result = i2c.read(0);
    i2c.stop();
    return (result);
    }
    
void writeByte(char address, char reg,char value)
// Sends 1 byte to an I2C address
{    
    i2c.start();
    i2c.write(address);         // Slave address
    i2c.write(reg);             // Subaddress (register)
    i2c.write(value);
    i2c.stop();
    
    }
    
void initSensors (void)
// Switch on and set up the 3 on-board sensors
{
    pc.printf("--------------------------------------\n");
    pc.printf("\nSTM MEMS eval board sensor init \n");
    
#ifdef LSM303_on
    // LSM303DLHC Magnetic sensor
    pc.printf("LSM303DLHC ping (should reply 0x48): %x \n",readByte(LSM303_m,mIRA_REG_M));
    writeByte(LSM303_m,mCRA_REG_M,0x94);     //switch on temperature sensor and set Output Data Rate to 30Hz
    writeByte(LSM303_m,mCRB_REG_M,0x20);     // Set the gain for +/- 1.3 Gauss full scale range
    writeByte(LSM303_m,mMR_REG_M,0x0);       // Continuous convertion mode
    
    // LSM303DLHC Accelerometer
    writeByte(LSM303_a,aCTRL_REG1_A ,0x37); // Set 25Hz ODR, everything else on
    writeByte(LSM303_a,aCTRL_REG4_A ,0x08); // Set full scale to +/- 2g sensitivity and high rez mode
#endif

#ifdef LPS331
    // LPS331 Pressure sensor
    pc.printf("LPS331 ping (should reply 0xBB): %x \n",readByte(LPS331addr,pWHO_AM_I));
    writeByte(LPS331addr,pCTRL_REG1,0x90);  // Switch on pressure sensor and select 1Hz ODR. If you select one-shot then sensor powers itself down after every reading...
    writeByte(LPS331addr,pRES_CONF,0x70);   // Temp and pressure noise reduction. Sets # of internal measurements that are averaged to 1 reading. Default is 0x7A (temp rez=128, press=512)
#endif

#ifdef L3GD20
    // L3GD20 gyro
    printf("Ping L3GD20 (should reply 0xD4): %x \n",readByte(L3GD20_ADDR,gWHO_AM_I));
    writeByte(L3GD20_ADDR,gCTRL_REG1,0x0F); // Set ODR to 95Hz, BW to 12.5Hz, enable axes and turn on device
    writeByte(L3GD20_ADDR,gCTRL_REG4,0x10); // Full scale selected at 500dps (degrees per second)
    printf("L3GD20 gyro Temp: %x degrees C \n",readByte(L3GD20_ADDR,gOUT_TEMP));
#endif
    
    pc.printf("--------------------------------------\n \n");
    wait(1); // Wait for settings to stabilize
    }    
    
void LPS331(SensorState_t state)
// Read the pressure sensor
{
    uint8_t             tempL,tempH,pressXL,pressL,pressH;
    int16_t             temp;
    int32_t             press24;
    float               pressure;
    
    // Measure temperature
    tempL=readByte(LPS331addr,pTEMP_OUT_L);
    tempH=readByte(LPS331addr,pTEMP_OUT_H);
    temp=(tempH << 8) | tempL; // 16-bit 2's complement data
    
    state.tempC=((float) temp / 480.0) + 42.5; // per equation on page 29 of the spec

    pc.printf("Pressure sensor temperature %.1f degreesC \n",state.tempC);
    
    // Pressure test
    pressXL=readByte(LPS331addr,pPRESS_OUT_XL);
    pressL=readByte(LPS331addr,pPRESS_OUT_L);
    pressH=readByte(LPS331addr,pPRESS_OUT_H);
    
    press24=(pressH << 16) | (pressL << 8) | pressXL ; // 24-bit 2's complement data
    pressure = (float)press24/4096.0; // Sensitivity is 4096 LSB per milibar
    
    pc.printf("Pressure %.1f mbars or %.1f inches Hg\n", pressure, (pressure*0.0295)+0.029);

    }

void LSM303 (SensorState_t * state)
// Magnetometer and accelerometer
{
    char        xL, xH, yL, yH, zL, zH;
    int16_t     mX, mY, mZ,aX,aY,aZ;
    float       pitch,roll,faX,faY;

    xL=readByte(LSM303_m,mOUT_X_L_M);
    xH=readByte(LSM303_m,mOUT_X_H_M);
    yL=readByte(LSM303_m,mOUT_Y_L_M);
    yH=readByte(LSM303_m,mOUT_Y_H_M);
    zL=readByte(LSM303_m,mOUT_Z_L_M);
    zH=readByte(LSM303_m,mOUT_Z_H_M);
    
    mX=(xH<<8) | (xL); // 16-bit 2's complement data
    mY=(yH<<8) | (yL);
    mZ=(zH<<8) | (zL);
    
    //pc.printf("mX=%hd   %X          mY=%hd  %X      mZ=%hd  %X      \n",mX,mX,mY,mY,mZ,mZ);
    
    mX=mX-Offset_mX; // These are callibration co-efficients to deal with non-zero soft iron magnetic offset
    mY=mY-Offset_mY; 
    
    xL=readByte(LSM303_a,aOUT_X_L_A);
    xH=readByte(LSM303_a,aOUT_X_H_A);
    yL=readByte(LSM303_a,aOUT_Y_L_A);
    yH=readByte(LSM303_a,aOUT_Y_H_A);
    zL=readByte(LSM303_a,aOUT_Z_L_A);
    zH=readByte(LSM303_a,aOUT_Z_H_A);

    aX=(signed short) ( (xH<<8) | (xL) ) >> 4; // 12-bit data from ADC. Cast ensures that the 2's complement sign is not lost in the right shift.
    aY=(signed short) ( (yH<<8) | (yL) ) >> 4;
    aZ=(signed short) ( (zH<<8) | (zL) ) >> 4;
    
    //pc.printf("aX=%hd   %X          aY=%hd  %X      aZ=%hd  %X      \n",aX,aX,aY,aY,aZ,aZ);
    
    faX=((float) aX) /2000.0; // Accelerometer scale I chose is 1mg per LSB with range +/-2g. So to normalize for full scale need to divide by 2000.
    faY=((float) aY) /2000.0; // If you don't do this the pitch and roll calcs will not work (inverse cosine of a value greater than 1)
    //faZ=((float) aZ) /2000.0; // Not used in a calc so comment out to avoid the compiler warning
        
    // Trigonometry derived from STM app note AN3192 and from WikiRobots
   pitch = asin((float) -faX*2); // Dividing faX and faY by 1000 rather than 2000 seems to give better tilt immunity. Do it here rather than above to preserve true mg units of faX etc
   roll = asin(faY*2/cos(pitch));
   
  float xh = mX * cos(pitch) + mZ * sin(pitch);
  float yh = mX * sin(roll) * sin(pitch) + mY * cos(roll) - mZ * sin(roll) * cos(pitch);
  float zh = -mX * cos(roll) * sin(pitch) + mY * sin(roll) + mZ * cos(roll) * cos(pitch);
 
  float heading = atan2(yh, xh) * RadtoDeg; // Note use of atan2 rather than atan since better for working with quadrants
  if (yh < 0)
    heading=360+heading;
    
    state->heading=heading;
    state->pitch=pitch;
    state->roll=roll;
    
    pc.printf("Orientation (deg):       Pitch: %5.1f         Roll: %5.1f          Heading: %5.1f     \n",pitch*RadtoDeg,roll*RadtoDeg,heading);
    pc.printf("Acceleration (mg):       Forward: %5hd       Left: %5hd          Up: %5hd \n",aX,aY,aZ);    
    
}

void    L3GD20(void) // Gyro
{
    char        xL, xH, yL, yH, zL, zH;
    int16_t     gX, gY, gZ;
    float       rorX,rorY,rorZ;
    
    xL=readByte(L3GD20_ADDR,gOUT_X_L);
    xH=readByte(L3GD20_ADDR,gOUT_X_H);
    yL=readByte(L3GD20_ADDR,gOUT_Y_L);
    yH=readByte(L3GD20_ADDR,gOUT_Y_H);
    zL=readByte(L3GD20_ADDR,gOUT_Z_L);
    zH=readByte(L3GD20_ADDR,gOUT_Z_H);
    
    gX=(xH<<8) | (xL); // 16-bit 2's complement data
    gY=(yH<<8) | (yL);
    gZ=(zH<<8) | (zL);
    
    rorX=(float) gX * (17.5/1000.0);    // At 500dps sensitivity, L3GD20 returns 17.5/1000 dps per digit
    rorY=(float) gY * (17.5/1000.0);
    rorZ=(float) gZ * (17.5/1000.0);

    pc.printf("Rate of rotation (dps):  X:%5.1f               Y:%5.1f              Z:%5.1f \n",rorX,rorY,rorZ);
    //pc.printf("gX: %x           gY: %x          gZ: %x \n",gX,gY,gZ);
    
}

int main()
{
    SensorState_t   state;
    initSensors();

    while(1)
    {
        
#ifdef LPS331_on
    LPS331(state);
#endif

#ifdef LSM303_on
    LSM303(&state);
#endif

#ifdef L3GD20
    L3GD20();
#endif
    
    pc.printf("\n");
    wait(.5);
    } 
}