enhancement proposals: float instead of double, init_MPU6050() and read_MPU6050() in dedicated functions

[dsyleixa]

hi,
As I got my new MPU6050 (addr 0x68), I have 2 proposals:

1st, in order to make the code quicker by calculation and execution, I would suggest to use float instead of double (on ARM MCUs >2x as fast).

2nd, additionally, I would suggest to put
init_MPU6050() and
read_MPU6050(float &yaw, float &pitch, float &roll)) // yaw: wishful enhancement
into 2 dedicated functions, to make the code more readable and more versatile for arbitrary calls in arbitrary setup() and loop() functions, perhaps even for usage by different IMUs, other than MPU6050:

/* Copyright (C) 2012 Kristian Lauszus, TKJ Electronics. All rights reserved.

 This software may be distributed and modified under the terms of the GNU
 General Public License version 2 (GPL2) as published by the Free Software
 Foundation and appearing in the file GPL2.TXT included in the packaging of
 this file. Please note that GPL2 Section 2[b] requires that all works based
 on this software must also be made publicly available under the terms of
 the GPL2 ("Copyleft").

 Contact information
 -------------------

 Kristian Lauszus, TKJ Electronics
 Web      :  http://www.tkjelectronics.com
 e-mail   :  [email protected]
 */

#include <Wire.h>
#include <Kalman.h> // Source: https://github.com/TKJElectronics/KalmanFilter

//#define RESTRICT_PITCH // Comment out to restrict roll to ±90deg instead - please read: http://www.freescale.com/files/sensors/doc/app_note/AN3461.pdf

Kalman kalmanX; // Create the Kalman instances
Kalman kalmanY;

/* IMU Data */
float accX, accY, accZ;
float gyroX, gyroY, gyroZ;
int16_t tempRaw;

float gyroXangle, gyroYangle; // Angle calculate using the gyro only
float compAngleX, compAngleY; // Calculated angle using a complementary filter
float kalAngleX, kalAngleY; // Calculated angle using a Kalman filter

uint32_t timer;
uint8_t i2cData[14]; // Buffer for I2C data

// TODO: Make calibration routine


void init_MPU6050() {
   
  i2cData[0] = 7; // Set the sample rate to 1000Hz - 8kHz/(7+1) = 1000Hz
  i2cData[1] = 0x00; // Disable FSYNC and set 260 Hz Acc filtering, 256 Hz Gyro filtering, 8 KHz sampling
  i2cData[2] = 0x00; // Set Gyro Full Scale Range to ±250deg/s
  i2cData[3] = 0x00; // Set Accelerometer Full Scale Range to ±2g
  while (i2cWrite(0x19, i2cData, 4, false)); // Write to all four registers at once
  while (i2cWrite(0x6B, 0x01, true)); // PLL with X axis gyroscope reference and disable sleep mode

  while (i2cRead(0x75, i2cData, 1));
  if (i2cData[0] != 0x68) { // Read "WHO_AM_I" register
    Serial.print(F("Error reading sensor"));
    while (1);
  }

  delay(100); // Wait for sensor to stabilize

  /* Set kalman and gyro starting angle */
  while (i2cRead(0x3B, i2cData, 6));
  accX = (int16_t)((i2cData[0] << 8) | i2cData[1]);
  accY = (int16_t)((i2cData[2] << 8) | i2cData[3]);
  accZ = (int16_t)((i2cData[4] << 8) | i2cData[5]);

  // Source: http://www.freescale.com/files/sensors/doc/app_note/AN3461.pdf eq. 25 and eq. 26
  // atan2 outputs the value of -π to π (radians) - see http://en.wikipedia.org/wiki/Atan2
  // It is then converted from radians to degrees
#ifdef RESTRICT_PITCH // Eq. 25 and 26
  float roll  = atan2(accY, accZ) * RAD_TO_DEG;
  float pitch = atan(-accX / sqrt(accY * accY + accZ * accZ)) * RAD_TO_DEG;
#else // Eq. 28 and 29
  float roll  = atan(accY / sqrt(accX * accX + accZ * accZ)) * RAD_TO_DEG;
  float pitch = atan2(-accX, accZ) * RAD_TO_DEG;
#endif

  kalmanX.setAngle(roll); // Set starting angle
  kalmanY.setAngle(pitch);
  gyroXangle = roll;
  gyroYangle = pitch;
  compAngleX = roll;
  compAngleY = pitch;

  timer = micros();
  
}


void read_MPU6050(float &yaw, float &pitch, float &roll) {
  /* Update all the values */
  while (i2cRead(0x3B, i2cData, 14));
  accX = (int16_t)((i2cData[0] << 8) | i2cData[1]);
  accY = (int16_t)((i2cData[2] << 8) | i2cData[3]);
  accZ = (int16_t)((i2cData[4] << 8) | i2cData[5]);
  tempRaw = (int16_t)((i2cData[6] << 8) | i2cData[7]);
  gyroX = (int16_t)((i2cData[8] << 8) | i2cData[9]);
  gyroY = (int16_t)((i2cData[10] << 8) | i2cData[11]);
  gyroZ = (int16_t)((i2cData[12] << 8) | i2cData[13]);;

  float dt = (float)(micros() - timer) / 1000000; // Calculate delta time
  timer = micros();

  // Source: http://www.freescale.com/files/sensors/doc/app_note/AN3461.pdf eq. 25 and eq. 26
  // atan2 outputs the value of -π to π (radians) - see http://en.wikipedia.org/wiki/Atan2
  // It is then converted from radians to degrees
#ifdef RESTRICT_PITCH // Eq. 25 and 26
  roll  = atan2(accY, accZ) * RAD_TO_DEG;
  pitch = atan(-accX / sqrt(accY * accY + accZ * accZ)) * RAD_TO_DEG;
#else // Eq. 28 and 29
  roll  = atan(accY / sqrt(accX * accX + accZ * accZ)) * RAD_TO_DEG;
  pitch = atan2(-accX, accZ) * RAD_TO_DEG;
#endif

  float gyroXrate = gyroX / 131.0; // Convert to deg/s
  float gyroYrate = gyroY / 131.0; // Convert to deg/s

#ifdef RESTRICT_PITCH
  // This fixes the transition problem when the accelerometer angle jumps between -180 and 180 degrees
  if ((roll < -90 && kalAngleX > 90) || (roll > 90 && kalAngleX < -90)) {
    kalmanX.setAngle(roll);
    compAngleX = roll;
    kalAngleX = roll;
    gyroXangle = roll;
  } else
    kalAngleX = kalmanX.getAngle(roll, gyroXrate, dt); // Calculate the angle using a Kalman filter

  if (abs(kalAngleX) > 90)
    gyroYrate = -gyroYrate; // Invert rate, so it fits the restriced accelerometer reading
  kalAngleY = kalmanY.getAngle(pitch, gyroYrate, dt);
#else
  // This fixes the transition problem when the accelerometer angle jumps between -180 and 180 degrees
  if ((pitch < -90 && kalAngleY > 90) || (pitch > 90 && kalAngleY < -90)) {
    kalmanY.setAngle(pitch);
    compAngleY = pitch;
    kalAngleY = pitch;
    gyroYangle = pitch;
  } else
    kalAngleY = kalmanY.getAngle(pitch, gyroYrate, dt); // Calculate the angle using a Kalman filter

  if (abs(kalAngleY) > 90)
    gyroXrate = -gyroXrate; // Invert rate, so it fits the restriced accelerometer reading
  kalAngleX = kalmanX.getAngle(roll, gyroXrate, dt); // Calculate the angle using a Kalman filter
#endif

  gyroXangle += gyroXrate * dt; // Calculate gyro angle without any filter
  gyroYangle += gyroYrate * dt;
  //gyroXangle += kalmanX.getRate() * dt; // Calculate gyro angle using the unbiased rate
  //gyroYangle += kalmanY.getRate() * dt;

  compAngleX = 0.93 * (compAngleX + gyroXrate * dt) + 0.07 * roll; // Calculate the angle using a Complimentary filter
  compAngleY = 0.93 * (compAngleY + gyroYrate * dt) + 0.07 * pitch;

  // Reset the gyro angle when it has drifted too much
  if (gyroXangle < -180 || gyroXangle > 180)
    gyroXangle = kalAngleX;
  if (gyroYangle < -180 || gyroYangle > 180)
    gyroYangle = kalAngleY;
}

 


void setup() {
  Serial.begin(115200);
  Wire.begin();
#if ARDUINO >= 157
  Wire.setClock(400000UL); // Set I2C frequency to 400kHz
#else
  TWBR = ((F_CPU / 400000UL) - 16) / 2; // Set I2C frequency to 400kHz
#endif

  init_MPU6050();

}


void loop() {

  float yaw=0, pitch=0, roll=0; // yaw: wishful enhancement

  read_MPU6050(yaw, pitch, roll);

    /* Print Data */
  #if 0 // Set to 1 to activate
  Serial.print(accX); Serial.print("\t");
  Serial.print(accY); Serial.print("\t");
  Serial.print(accZ); Serial.print("\t");

  Serial.print(gyroX); Serial.print("gyroX\t");
  Serial.print(gyroY); Serial.print("gyroY\t");
  Serial.print(gyroZ); Serial.print("gyroZ\t");

  Serial.print("\t");
#endif

  Serial.print("roll="); Serial.print(roll); Serial.print(" \t");
  //Serial.print(gyroXangle); Serial.print("\t");
  //Serial.print(compAngleX); Serial.print("\t");
  //Serial.print(kalAngleX); Serial.print("\t");

  Serial.print("\t");

  Serial.print("pitch="); Serial.print(pitch); Serial.print(" \t");
  
  //Serial.print(gyroYangle); Serial.print("\t");
  //Serial.print(compAngleY); Serial.print("\t");
  //Serial.print(kalAngleY); Serial.print("\t");

#if 0 // Set to 1 to print the temperature
  Serial.print("\t");

  float temperature = (float)tempRaw / 340.0 + 36.53;
  Serial.print(temperature); Serial.print("\t");
#endif

  Serial.print("\r\n");
  delay(2);
  
}

what would you think?

[Lauszus]

@dsyleixa sure, you're more than welcome to open up a PR.

[dsyleixa]

as stated, I have no idea how a PR works, I just use github to download files and libs. But feel free to use that for your next lib update if you agree to me and if you like that!

[Theara-Seng]

@Lauszus @dsyleixa If I want to read the yaw angle, can you recommend me something? I want to use it in 4 wheeled mobile robot