Reading magnetometer BMX055 in I2C

[MinhNhat]

Hi everyone,

I am working with the BMX055 sensor and using I2C to communicate.

The data value of the accelerometer and gyroscope is correct but the raw data from the magnetometer is quite weird. 

I tried to change the direction of the BMX055 sensor in few degrees but its output raw value did not change and. However, when I rotated it in 90 degrees or more the output value of the magnetometer is changed a lot.

Blue: x-axis

Green: y-axis

Red: z-axis

This my code to read the value of the accelerometer, gyroscope, and magnetometer.

#include<Wire.h>
// BMX055　加速度センサのI2Cアドレス  
#define Addr_Accl 0x19  // (JP1,JP2,JP3 = Openの時)
// BMX055　ジャイロセンサのI2Cアドレス
#define Addr_Gyro 0x69  // (JP1,JP2,JP3 = Openの時)
// BMX055　磁気センサのI2Cアドレス
#define Addr_Mag 0x13   // (JP1,JP2,JP3 = Openの時)

// センサーの値を保存するグローバル関数
float xAccl = 0.00;
float yAccl = 0.00;
float zAccl = 0.00;
float xGyro = 0.00;
float yGyro = 0.00;
float zGyro = 0.00;
int   xMag  = 0;
int   yMag  = 0;
int   zMag  = 0;

void setup()
{
  // Wire(Arduino-I2C)の初期化
  Wire.begin();
  // デバック用シリアル通信は9600bps
  Serial.begin(9600);
  //BMX055 初期化
  BMX055_Init();
  delay(100);
}

void loop()
{
  Serial.println("--------------------------------------"); 

  //BMX055 加速度の読み取り
  BMX055_Accl();
  //Serial.print("Accl= ");
  Serial.println(xAccl);
  //Serial.print(",");
  Serial.println(yAccl);
  //Serial.print(",");
  Serial.println(zAccl);
  //Serial.println(""); 
  
  //BMX055 ジャイロの読み取り
  BMX055_Gyro();
  //Serial.print("Gyro= ");
  Serial.println(xGyro);
  //Serial.print(",");
  Serial.println(yGyro);
  //Serial.print(",");
  Serial.println(zGyro);
  //Serial.println(""); 
  
  //BMX055 磁気の読み取り
  BMX055_Mag();
  //Serial.print("Mag= ");
  Serial.println(xMag);
  //Serial.print(",");
  Serial.println(yMag);
  //Serial.print(",");
  Serial.println(zMag);
  //Serial.println(""); 
  
  delay(10);
}

//=====================================================================================//
void BMX055_Init()
{
  //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Accl);
  Wire.write(0x0F); // Select PMU_Range register
  Wire.write(0x03);   // Range = +/- 2g
  Wire.endTransmission();
  delay(100);
 //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Accl);
  Wire.write(0x10);  // Select PMU_BW register
  Wire.write(0x08);  // Bandwidth = 7.81 Hz
  Wire.endTransmission();
  delay(100);
  //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Accl);
  Wire.write(0x11);  // Select PMU_LPW register
  Wire.write(0x00);  // Normal mode, Sleep duration = 0.5ms
  Wire.endTransmission();
  delay(100);
 //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Gyro);
  Wire.write(0x0F);  // Select Range register
  Wire.write(0x04);  // Full scale = +/- 125 degree/s
  Wire.endTransmission();
  delay(100);
 //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Gyro);
  Wire.write(0x10);  // Select Bandwidth register
  Wire.write(0x07);  // ODR = 100 Hz
  Wire.endTransmission();
  delay(100);
 //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Gyro);
  Wire.write(0x11);  // Select LPM1 register
  Wire.write(0x00);  // Normal mode, Sleep duration = 2ms
  Wire.endTransmission();
  delay(100);
 //------------------------------------------------------------//


//// Addr_Mag 0x13
  Wire.beginTransmission(Addr_Mag);
  Wire.write(0x4B);  // Select Mag register
  Wire.write(0x83);  // Soft reset
  Wire.endTransmission();
  delay(100);
  //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Mag);
  Wire.write(0x4B);  // Select Mag register
  Wire.write(0x01);  // Soft reset
  Wire.endTransmission();
  delay(100);
  //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Mag);
  Wire.write(0x4C);  // Select Mag register
  Wire.write(0x00);  // Normal Mode, ODR = 10 Hz
  Wire.endTransmission();
 //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Mag);
  Wire.write(0x4E);  // Select Mag register
  Wire.write(0x84);  // X, Y, Z-Axis enabled
  Wire.endTransmission();
 //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Mag);
  Wire.write(0x51);  // Select Mag register
  Wire.write(0x04);  // No. of Repetitions for X-Y Axis = 9
  Wire.endTransmission();
 //------------------------------------------------------------//
  Wire.beginTransmission(Addr_Mag);
  Wire.write(0x52);  // Select Mag register
  Wire.write(0x16);  // No. of Repetitions for Z-Axis = 15
  Wire.endTransmission();
}
//=====================================================================================//
void BMX055_Accl()
{
  int data[6];
  for (int i = 0; i < 6; i++)
  {
    Wire.beginTransmission(Addr_Accl);
    Wire.write((2 + i));// Select data register
    Wire.endTransmission();
    Wire.requestFrom(Addr_Accl, 1);// Request 1 byte of data
    // Read 6 bytes of data
    // xAccl lsb, xAccl msb, yAccl lsb, yAccl msb, zAccl lsb, zAccl msb
    if (Wire.available() == 1)
      data[i] = Wire.read();
  }
  // Convert the data to 12-bits
  xAccl = ((data[1] * 256) + (data[0] & 0xF0)) / 16;
  Serial.println("here");
  if (xAccl > 2047)  xAccl -= 4096;
  yAccl = ((data[3] * 256) + (data[2] & 0xF0)) / 16;
  if (yAccl > 2047)  yAccl -= 4096;
  zAccl = ((data[5] * 256) + (data[4] & 0xF0)) / 16;
  if (zAccl > 2047)  zAccl -= 4096;
  xAccl = xAccl * 0.0098; // renge +-2g
  yAccl = yAccl * 0.0098; // renge +-2g
  zAccl = zAccl * 0.0098; // renge +-2g
}
//=====================================================================================//
void BMX055_Gyro()
{
  int data[6];
  for (int i = 0; i < 6; i++)
  {
    Wire.beginTransmission(Addr_Gyro);
    Wire.write((2 + i));    // Select data register
    Wire.endTransmission();
    Wire.requestFrom(Addr_Gyro, 1);    // Request 1 byte of data
    // Read 6 bytes of data
    // xGyro lsb, xGyro msb, yGyro lsb, yGyro msb, zGyro lsb, zGyro msb
    if (Wire.available() == 1)
      data[i] = Wire.read();
  }
  // Convert the data
  xGyro = (data[1] * 256) + data[0];
  if (xGyro > 32767)  xGyro -= 65536;
  yGyro = (data[3] * 256) + data[2];
  if (yGyro > 32767)  yGyro -= 65536;
  zGyro = (data[5] * 256) + data[4];
  if (zGyro > 32767)  zGyro -= 65536;

  xGyro = xGyro * 0.0038; //  Full scale = +/- 125 degree/s
  yGyro = yGyro * 0.0038; //  Full scale = +/- 125 degree/s
  zGyro = zGyro * 0.0038; //  Full scale = +/- 125 degree/s
}
//=====================================================================================//
void BMX055_Mag()
{
  int data[8];
  for (int i = 0; i < 8; i++)
  {
    Wire.beginTransmission(Addr_Mag);
    Wire.write((0x42 + i));    // Select data register
    Wire.endTransmission();
    Wire.requestFrom(Addr_Mag, 1);    // Request 1 byte of data
    // Read 6 bytes of data
    // xMag lsb, xMag msb, yMag lsb, yMag msb, zMag lsb, zMag msb
    if (Wire.available() == 1)
      data[i] = Wire.read();
  }
  // Convert the data
  xMag = ((data[1] <<8) | (data[0]>>3));
  if (xMag > 4095)  xMag -= 8192;
  yMag = ((data[3] <<8) | (data[2]>>3));
  if (yMag > 4095)  yMag -= 8192;
  zMag = ((data[5] <<8) | (data[4]>>3));
  if (zMag > 16383)  zMag -= 32768;
}

My question is:

1> Is this the correct way(correct registers) to read the magnetometer data?

2> If my code is correct, what happens to my magnetometer raw data?

Thank you

[Jet]

Hi Sir:

     Recommend you to read the offecial BMM150 api code to know how to get the magetometer data.  I don't see you to use trim values after you read the mag data registers.

     Please see the following link:

     https://www.bosch-sensortec.com/products/motion-sensors/absolute-orientation-sensors/absolute-orient...

     Hopefully, it can help you.