Basic Tilt Sensor (MPU-6050) Example

Basic Tilt Sensor (MPU-6050) Example

Simple Arduino example to print out rotation values (in angles) using an MPU-6050 gyro and accelerometer sensor. The sensor can actually generate more data, but this basic example provides rotation about two axes (x- and y-).

Components

1 x MPU-6050 gyro + accelerometer sensor (for rotation)
1 x Arduino Uno
1 x breadboard
jumper wires
 

Setup

Arduino sketch

Inspect Serial monitor (9600) for x- and y- rotations in degrees. Note that SDA and SCL connections cannot change; these are special pins assigned to A4 and A5 on the Arduino Uno.

// uses Wire library: http://arduino.cc/en/reference/wire
// on Arduino uno:
//   VCC to 5V; GND to GND
//   SDA to A4; SCL to A5
// MPU-6050 Accelerometer + Gyro
// -----------------------------
//
// Adapted from arduino.cc user "Krodal".
// June 2012
// Open Source / Public Domain
//
// Using Arduino 1.0.1
// It will not work with an older version, 
// since Wire.endTransmission() uses a parameter 
// to hold or release the I2C bus.
//
// Documentation:
// - The InvenSense documents:
//   - "MPU-6000 and MPU-6050 Product Specification",
//     PS-MPU-6000A.pdf
//   - "MPU-6000 and MPU-6050 Register Map and Descriptions",
//     RM-MPU-6000A.pdf or RS-MPU-6000A.pdf
//   - "MPU-6000/MPU-6050 9-Axis Evaluation Board User Guide"
//     AN-MPU-6000EVB.pdf
// 
// The accuracy is 16-bits.
//
// Temperature sensor from -40 to +85 degrees Celsius
//   340 per degrees, -512 at 35 degrees.
//
// At power-up, all registers are zero, except these two:
//      Register 0x6B (PWR_MGMT_2) = 0x40  (I read zero).
//      Register 0x75 (WHO_AM_I)   = 0x68.
// 

#include 

// The name of the sensor is "MPU-6050".
// For program code, I omit the '-', 
// therefor I use the name "MPU6050....".


// Register names according to the datasheet.
// According to the InvenSense document 
// "MPU-6000 and MPU-6050 Register Map 
// and Descriptions Revision 3.2", there are no registers
// at 0x02 ... 0x18, but according other information 
// the registers in that unknown area are for gain 
// and offsets.
// 
#define MPU6050_AUX_VDDIO          0x01   // R/W
#define MPU6050_SMPLRT_DIV         0x19   // R/W
#define MPU6050_CONFIG             0x1A   // R/W
#define MPU6050_GYRO_CONFIG        0x1B   // R/W
#define MPU6050_ACCEL_CONFIG       0x1C   // R/W
#define MPU6050_FF_THR             0x1D   // R/W
#define MPU6050_FF_DUR             0x1E   // R/W
#define MPU6050_MOT_THR            0x1F   // R/W
#define MPU6050_MOT_DUR            0x20   // R/W
#define MPU6050_ZRMOT_THR          0x21   // R/W
#define MPU6050_ZRMOT_DUR          0x22   // R/W
#define MPU6050_FIFO_EN            0x23   // R/W
#define MPU6050_I2C_MST_CTRL       0x24   // R/W
#define MPU6050_I2C_SLV0_ADDR      0x25   // R/W
#define MPU6050_I2C_SLV0_REG       0x26   // R/W
#define MPU6050_I2C_SLV0_CTRL      0x27   // R/W
#define MPU6050_I2C_SLV1_ADDR      0x28   // R/W
#define MPU6050_I2C_SLV1_REG       0x29   // R/W
#define MPU6050_I2C_SLV1_CTRL      0x2A   // R/W
#define MPU6050_I2C_SLV2_ADDR      0x2B   // R/W
#define MPU6050_I2C_SLV2_REG       0x2C   // R/W
#define MPU6050_I2C_SLV2_CTRL      0x2D   // R/W
#define MPU6050_I2C_SLV3_ADDR      0x2E   // R/W
#define MPU6050_I2C_SLV3_REG       0x2F   // R/W
#define MPU6050_I2C_SLV3_CTRL      0x30   // R/W
#define MPU6050_I2C_SLV4_ADDR      0x31   // R/W
#define MPU6050_I2C_SLV4_REG       0x32   // R/W
#define MPU6050_I2C_SLV4_DO        0x33   // R/W
#define MPU6050_I2C_SLV4_CTRL      0x34   // R/W
#define MPU6050_I2C_SLV4_DI        0x35   // R  
#define MPU6050_I2C_MST_STATUS     0x36   // R
#define MPU6050_INT_PIN_CFG        0x37   // R/W
#define MPU6050_INT_ENABLE         0x38   // R/W
#define MPU6050_INT_STATUS         0x3A   // R  
#define MPU6050_ACCEL_XOUT_H       0x3B   // R  
#define MPU6050_ACCEL_XOUT_L       0x3C   // R  
#define MPU6050_ACCEL_YOUT_H       0x3D   // R  
#define MPU6050_ACCEL_YOUT_L       0x3E   // R  
#define MPU6050_ACCEL_ZOUT_H       0x3F   // R  
#define MPU6050_ACCEL_ZOUT_L       0x40   // R  
#define MPU6050_TEMP_OUT_H         0x41   // R  
#define MPU6050_TEMP_OUT_L         0x42   // R  
#define MPU6050_GYRO_XOUT_H        0x43   // R  
#define MPU6050_GYRO_XOUT_L        0x44   // R  
#define MPU6050_GYRO_YOUT_H        0x45   // R  
#define MPU6050_GYRO_YOUT_L        0x46   // R  
#define MPU6050_GYRO_ZOUT_H        0x47   // R  
#define MPU6050_GYRO_ZOUT_L        0x48   // R  
#define MPU6050_EXT_SENS_DATA_00   0x49   // R  
#define MPU6050_EXT_SENS_DATA_01   0x4A   // R  
#define MPU6050_EXT_SENS_DATA_02   0x4B   // R  
#define MPU6050_EXT_SENS_DATA_03   0x4C   // R  
#define MPU6050_EXT_SENS_DATA_04   0x4D   // R  
#define MPU6050_EXT_SENS_DATA_05   0x4E   // R  
#define MPU6050_EXT_SENS_DATA_06   0x4F   // R  
#define MPU6050_EXT_SENS_DATA_07   0x50   // R  
#define MPU6050_EXT_SENS_DATA_08   0x51   // R  
#define MPU6050_EXT_SENS_DATA_09   0x52   // R  
#define MPU6050_EXT_SENS_DATA_10   0x53   // R  
#define MPU6050_EXT_SENS_DATA_11   0x54   // R  
#define MPU6050_EXT_SENS_DATA_12   0x55   // R  
#define MPU6050_EXT_SENS_DATA_13   0x56   // R  
#define MPU6050_EXT_SENS_DATA_14   0x57   // R  
#define MPU6050_EXT_SENS_DATA_15   0x58   // R  
#define MPU6050_EXT_SENS_DATA_16   0x59   // R  
#define MPU6050_EXT_SENS_DATA_17   0x5A   // R  
#define MPU6050_EXT_SENS_DATA_18   0x5B   // R  
#define MPU6050_EXT_SENS_DATA_19   0x5C   // R  
#define MPU6050_EXT_SENS_DATA_20   0x5D   // R  
#define MPU6050_EXT_SENS_DATA_21   0x5E   // R  
#define MPU6050_EXT_SENS_DATA_22   0x5F   // R  
#define MPU6050_EXT_SENS_DATA_23   0x60   // R  
#define MPU6050_MOT_DETECT_STATUS  0x61   // R  
#define MPU6050_I2C_SLV0_DO        0x63   // R/W
#define MPU6050_I2C_SLV1_DO        0x64   // R/W
#define MPU6050_I2C_SLV2_DO        0x65   // R/W
#define MPU6050_I2C_SLV3_DO        0x66   // R/W
#define MPU6050_I2C_MST_DELAY_CTRL 0x67   // R/W
#define MPU6050_SIGNAL_PATH_RESET  0x68   // R/W
#define MPU6050_MOT_DETECT_CTRL    0x69   // R/W
#define MPU6050_USER_CTRL          0x6A   // R/W
#define MPU6050_PWR_MGMT_1         0x6B   // R/W
#define MPU6050_PWR_MGMT_2         0x6C   // R/W
#define MPU6050_FIFO_COUNTH        0x72   // R/W
#define MPU6050_FIFO_COUNTL        0x73   // R/W
#define MPU6050_FIFO_R_W           0x74   // R/W
#define MPU6050_WHO_AM_I           0x75   // R


// Defines for the bits, to be able to change 
// between bit number and binary definition.
// By using the bit number, programming the sensor 
// is like programming the AVR microcontroller.
// But instead of using "(1< 40 )
     digitalWrite( xLED_PIN, HIGH );
  else
    digitalWrite( xLED_PIN, LOW );
    
  if ( yRotation > 40 )
     digitalWrite( yLED_PIN, HIGH );
  else
    digitalWrite( yLED_PIN, LOW );

  // Delay so we don't swamp the serial port
  delay(1000);
}








void set_last_read_angle_data(unsigned long time, float x, float y, float z, float x_gyro, float y_gyro, float z_gyro) {
  last_read_time = time;
  last_x_angle = x;
  last_y_angle = y;
  last_z_angle = z;
  last_gyro_x_angle = x_gyro;
  last_gyro_y_angle = y_gyro;
  last_gyro_z_angle = z_gyro;
}

inline unsigned long get_last_time() {return last_read_time;}
inline float get_last_x_angle() {return last_x_angle;}
inline float get_last_y_angle() {return last_y_angle;}
inline float get_last_z_angle() {return last_z_angle;}
inline float get_last_gyro_x_angle() {return last_gyro_x_angle;}
inline float get_last_gyro_y_angle() {return last_gyro_y_angle;}
inline float get_last_gyro_z_angle() {return last_gyro_z_angle;}

//  Use the following global variables and access functions
//  to calibrate the acceleration sensor
float    base_x_accel;
float    base_y_accel;
float    base_z_accel;

float    base_x_gyro;
float    base_y_gyro;
float    base_z_gyro;


int read_gyro_accel_vals(uint8_t* accel_t_gyro_ptr) {
  // Read the raw values.
  // Read 14 bytes at once, 
  // containing acceleration, temperature and gyro.
  // With the default settings of the MPU-6050,
  // there is no filter enabled, and the values
  // are not very stable.  Returns the error value
  
  accel_t_gyro_union* accel_t_gyro = (accel_t_gyro_union *) accel_t_gyro_ptr;
   
  int error = MPU6050_read (MPU6050_ACCEL_XOUT_H, (uint8_t *) accel_t_gyro, sizeof(*accel_t_gyro));

  // Swap all high and low bytes.
  // After this, the registers values are swapped, 
  // so the structure name like x_accel_l does no 
  // longer contain the lower byte.
  uint8_t swap;
  #define SWAP(x,y) swap = x; x = y; y = swap

  SWAP ((*accel_t_gyro).reg.x_accel_h, (*accel_t_gyro).reg.x_accel_l);
  SWAP ((*accel_t_gyro).reg.y_accel_h, (*accel_t_gyro).reg.y_accel_l);
  SWAP ((*accel_t_gyro).reg.z_accel_h, (*accel_t_gyro).reg.z_accel_l);
  SWAP ((*accel_t_gyro).reg.t_h, (*accel_t_gyro).reg.t_l);
  SWAP ((*accel_t_gyro).reg.x_gyro_h, (*accel_t_gyro).reg.x_gyro_l);
  SWAP ((*accel_t_gyro).reg.y_gyro_h, (*accel_t_gyro).reg.y_gyro_l);
  SWAP ((*accel_t_gyro).reg.z_gyro_h, (*accel_t_gyro).reg.z_gyro_l);

  return error;
}

// The sensor should be motionless on a horizontal surface 
//  while calibration is happening
void calibrate_sensors() {
  int                   num_readings = 10;
  float                 x_accel = 0;
  float                 y_accel = 0;
  float                 z_accel = 0;
  float                 x_gyro = 0;
  float                 y_gyro = 0;
  float                 z_gyro = 0;
  accel_t_gyro_union    accel_t_gyro;
  
  //Serial.println("Starting Calibration");

  // Discard the first set of values read from the IMU
  read_gyro_accel_vals((uint8_t *) &accel_t_gyro);
  
  // Read and average the raw values from the IMU
  for (int i = 0; i < num_readings; i++) {
    read_gyro_accel_vals((uint8_t *) &accel_t_gyro);
    x_accel += accel_t_gyro.value.x_accel;
    y_accel += accel_t_gyro.value.y_accel;
    z_accel += accel_t_gyro.value.z_accel;
    x_gyro += accel_t_gyro.value.x_gyro;
    y_gyro += accel_t_gyro.value.y_gyro;
    z_gyro += accel_t_gyro.value.z_gyro;
    delay(100);
  }
  x_accel /= num_readings;
  y_accel /= num_readings;
  z_accel /= num_readings;
  x_gyro /= num_readings;
  y_gyro /= num_readings;
  z_gyro /= num_readings;
  
  // Store the raw calibration values globally
  base_x_accel = x_accel;
  base_y_accel = y_accel;
  base_z_accel = z_accel;
  base_x_gyro = x_gyro;
  base_y_gyro = y_gyro;
  base_z_gyro = z_gyro;
  
  Serial.println("Finishing Calibration");
}


void initTiltSensor()
{      
  int error;
  uint8_t c;

  // Initialize the 'Wire' class for the I2C-bus.
  Wire.begin();

  pinMode( xLED_PIN, OUTPUT );
  pinMode( yLED_PIN, OUTPUT );

  // default at power-up:
  //    Gyro at 250 degrees second
  //    Acceleration at 2g
  //    Clock source at internal 8MHz
  //    The device is in sleep mode.
  //

  error = MPU6050_read (MPU6050_WHO_AM_I, &c, 1);
  
  // According to the datasheet, the 'sleep' bit
  // should read a '1'. But I read a '0'.
  // That bit has to be cleared, since the sensor
  // is in sleep mode at power-up. Even if the
  // bit reads '0'.
  error = MPU6050_read (MPU6050_PWR_MGMT_2, &c, 1);
  // Clear the 'sleep' bit to start the sensor.
  MPU6050_write_reg (MPU6050_PWR_MGMT_1, 0);
  
  //Initialize the angles
  calibrate_sensors();  
  set_last_read_angle_data(millis(), 0, 0, 0, 0, 0, 0);
}


void readTiltData()
{
  int error;
  double dT;
  accel_t_gyro_union accel_t_gyro;

  // Read the raw values.
  error = read_gyro_accel_vals((uint8_t*) &accel_t_gyro);
  
  // Get the time of reading for rotation computations
  unsigned long t_now = millis();
   
  // Convert gyro values to degrees/sec
  float FS_SEL = 131;
  float gyro_x = (accel_t_gyro.value.x_gyro - base_x_gyro)/FS_SEL;
  float gyro_y = (accel_t_gyro.value.y_gyro - base_y_gyro)/FS_SEL;
  float gyro_z = (accel_t_gyro.value.z_gyro - base_z_gyro)/FS_SEL;
  
  
  // Get raw acceleration values
  //float G_CONVERT = 16384;
  float accel_x = accel_t_gyro.value.x_accel;
  float accel_y = accel_t_gyro.value.y_accel;
  float accel_z = accel_t_gyro.value.z_accel;
  
  // Get angle values from accelerometer
  float RADIANS_TO_DEGREES = 180/3.14159;
//  float accel_vector_length = sqrt(pow(accel_x,2) + pow(accel_y,2) + pow(accel_z,2));
  float accel_angle_y = atan(-1*accel_x/sqrt(pow(accel_y,2) + pow(accel_z,2)))*RADIANS_TO_DEGREES;
  float accel_angle_x = atan(accel_y/sqrt(pow(accel_x,2) + pow(accel_z,2)))*RADIANS_TO_DEGREES;

  float accel_angle_z = 0;
  
  // Compute the (filtered) gyro angles
  float dt =(t_now - get_last_time())/1000.0;
  float gyro_angle_x = gyro_x*dt + get_last_x_angle();
  float gyro_angle_y = gyro_y*dt + get_last_y_angle();
  float gyro_angle_z = gyro_z*dt + get_last_z_angle();
  
  // Compute the drifting gyro angles
  float unfiltered_gyro_angle_x = gyro_x*dt + get_last_gyro_x_angle();
  float unfiltered_gyro_angle_y = gyro_y*dt + get_last_gyro_y_angle();
  float unfiltered_gyro_angle_z = gyro_z*dt + get_last_gyro_z_angle();
  
  // Apply the complementary filter to figure out the change in angle - choice of alpha is
  // estimated now.  Alpha depends on the sampling rate...
  float alpha = 0.96;
  float angle_x = alpha*gyro_angle_x + (1.0 - alpha)*accel_angle_x;
  float angle_y = alpha*gyro_angle_y + (1.0 - alpha)*accel_angle_y;
  float angle_z = gyro_angle_z;  //Accelerometer doesn't give z-angle
  
  // Update the saved data with the latest values
  set_last_read_angle_data(t_now, angle_x, angle_y, angle_z, unfiltered_gyro_angle_x, unfiltered_gyro_angle_y, unfiltered_gyro_angle_z);

  // save in global variables
  xRotation = angle_x;
  yRotation = angle_y;
}


// --------------------------------------------------------
// MPU6050_read
//
// This is a common function to read multiple bytes 
// from an I2C device.
//
// It uses the boolean parameter for Wire.endTransMission()
// to be able to hold or release the I2C-bus. 
// This is implemented in Arduino 1.0.1.
//
// Only this function is used to read. 
// There is no function for a single byte.
//
int MPU6050_read(int start, uint8_t *buffer, int size)
{
  int i, n, error;

  Wire.beginTransmission(MPU6050_I2C_ADDRESS);
  n = Wire.write(start);
  if (n != 1)
    return (-10);

  n = Wire.endTransmission(false);    // hold the I2C-bus
  if (n != 0)
    return (n);

  // Third parameter is true: relase I2C-bus after data is read.
  Wire.requestFrom(MPU6050_I2C_ADDRESS, size, true);
  i = 0;
  while(Wire.available() && i< size)
  {
    buffer[i++]=Wire.read();
  }
  if ( i != size)
    return (-11);

  return (0);  // return : no error
}


// --------------------------------------------------------
// MPU6050_write
//
// This is a common function to write multiple bytes to an I2C device.
//
// If only a single register is written,
// use the function MPU_6050_write_reg().
//
// Parameters:
//   start : Start address, use a define for the register
//   pData : A pointer to the data to write.
//   size  : The number of bytes to write.
//
// If only a single register is written, a pointer
// to the data has to be used, and the size is
// a single byte:
//   int data = 0;        // the data to write
//   MPU6050_write (MPU6050_PWR_MGMT_1, &c, 1);
//
int MPU6050_write(int start, const uint8_t *pData, int size)
{
  int n, error;

  Wire.beginTransmission(MPU6050_I2C_ADDRESS);
  n = Wire.write(start);        // write the start address
  if (n != 1)
    return (-20);

  n = Wire.write(pData, size);  // write data bytes
  if (n != size)
    return (-21);

  error = Wire.endTransmission(true); // release the I2C-bus
  if (error != 0)
    return (error);

  return (0);         // return : no error
}

// --------------------------------------------------------
// MPU6050_write_reg
//
// An extra function to write a single register.
// It is just a wrapper around the MPU_6050_write()
// function, and it is only a convenient function
// to make it easier to write a single register.
//
int MPU6050_write_reg(int reg, uint8_t data)
{
  int error;

  error = MPU6050_write(reg, &data, 1);

  return (error);
}