Read acceleration sensor MPU-6050 with ATMega 16A

(Deutsche Version) In this post, I will show how to read the values of an MPU-6050 with an ATMega 16A. For the usage of I2C on the ATMega, I use this implementation.

If you want to use a Raspberry PI instead of an ATMega, see this post.

At first, I wrote two functions which can read from a register respectively write to a register:

void TWIM_WriteRegister(char reg, char value)
{
    TWIM_Start(addr, TWIM_WRITE); // set device address and write mode
    TWIM_Write(reg);
    TWIM_Write(value);
    TWIM_Stop();
}

char TWIM_ReadRegister(char reg)
{
    TWIM_Start(addr, TWIM_WRITE);
    TWIM_Write(reg);
    TWIM_Stop();

    TWIM_Start(addr, TWIM_READ); // set device address and read mode
    char ret = TWIM_ReadNack();
    TWIM_Stop();
    return ret;
}

As a second step, I wrote two functions which read the acceleration and gyro data from the Sensor. Please note that you have to disable the sleep mode, this can be done by using TWIM_WriteRegister(107, 0).

double MPU6050_ReadAccel(int axis)//x = 0; y = 1; z = 2
{
  char reg = axis * 2 + 59;
  char AFS_SEL = TWIM_ReadRegister(28);
  double factor = 1<<AFS_SEL;
  factor = 16384/factor;
  int val = 0;
  double double_val = 0;
  char ret = 0;

  ret = TWIM_ReadRegister(reg);
  val = ret << 8;

  ret = TWIM_ReadRegister(reg+1);  
  val += ret;

  if (val & 1<<15)
  val -= 1<<16;
  
  double_val = val;

  double_val = double_val / factor;

  return double_val;
}

double MPU6050_ReadGyro(int axis)//x = 0; y = 1; z = 2
{
  char reg = axis * 2 + 67;
  char FS_SEL = TWIM_ReadRegister(27);
  double factor = 1<<FS_SEL;
  factor = 131/factor;
  int val = 0;
  double double_val = 0;
  char ret = 0;

  ret = TWIM_ReadRegister(reg);
  val = ret << 8;

  ret = TWIM_ReadRegister(reg+1);  
  val += ret;

  if (val & 1<<15)
  val -= 1<<16;


  double_val = val;
 
  double_val = double_val / factor;

  return double_val;
}

The values for the gyrometer are in degrees per second and in units of g for the accelerometer, further information is provided in the Register Map, especially at the explaination of FS_SEL and AFS_SEL: http://www.invensense.com/mems/gyro/documents/RM-MPU-6000A.pdf