Arduino—— MPU9250

MPU9250+Arduino        sparkfun      https://learn.sparkfun.com/tutorials/mpu-9250-hookup-guide
下文的內容來自於sparkfun網站中的MPU9250教程。教程中軟硬件講的很清晰，同時還包括許多擴展閱讀，受益良多。這篇筆記會寫一下如何使用MPU9250傳感器，通過Arduino/Genuino101獲取傳感器數據，並分析該教程中提供的代碼文件提供的接口。本人菜鳥新手，這篇文章只是學習記錄一些新的知識，以供以後參考。

一、接線與庫文件配置

MPU9250傳感器和Arduino的連線方式如下：VCC->3.3V；GND->GND；SDA->A4；SCL->A5。
在Arduino IDE中的配置：在正確選擇Arduino硬件型號和連接端口之後，選擇項目->加載庫->管理庫打開庫管理器，在搜索欄中輸入“SparkFun MPU-9250”安裝該庫。

然後新建一個空白腳本，將下一節中的代碼粘貼在腳本中，編譯並上傳到Arduino中就可以正常運行代碼了。在工具->串口監視器中看到輸出的數字就是從MPU9250傳感器中讀取的信息。

二、代碼

原始代碼包含了在LCD顯示屏中的控制功能，下面的代碼不包括這一功能。另外我保留了部分原始註釋。如果只是讀取傳感器數據需要保證第三行的#define AHRS爲false，如果需要輸出傳感器位姿，則需要修改爲true。

#include "quaternionFilters.h"
#include "MPU9250.h"

#define AHRS false
#define SerialDebug true

// Pin definitions
int intPin = 12;  // These can be changed, 2 and 3 are the Arduinos ext int pins
int myLed  = 13;  // Set up pin 13 led for toggling

#define I2Cclock 400000
#define I2Cport Wire
#define MPU9250_ADDRESS MPU9250_ADDRESS_AD0   // Use either this line or the next to select which I2C address your device is using
//#define MPU9250_ADDRESS MPU9250_ADDRESS_AD1

MPU9250 myIMU(MPU9250_ADDRESS, I2Cport, I2Cclock);

void setup()
{
  Wire.begin();
  // TWBR = 12;  // 400 kbit/sec I2C speed
  Serial.begin(9600);

  while(!Serial){};

  // Set up the interrupt pin, its set as active high, push-pull
  pinMode(intPin, INPUT);
  digitalWrite(intPin, LOW);
  pinMode(myLed, OUTPUT);
  digitalWrite(myLed, HIGH);

  // Read the WHO_AM_I register, this is a good test of communication
  byte c = myIMU.readByte(MPU9250_ADDRESS, WHO_AM_I_MPU9250);
  Serial.print(F("MPU9250 I AM 0x"));
  Serial.print(c, HEX);
  Serial.print(F(" I should be 0x"));
  Serial.println(0x71, HEX);

  if (c == 0x71) // WHO_AM_I should always be 0x71
  {
    Serial.println(F("MPU9250 is online..."));

    // Start by performing self test and reporting values
    myIMU.MPU9250SelfTest(myIMU.selfTest);
    Serial.print(F("x-axis self test: acceleration trim within : "));
    Serial.print(myIMU.selfTest[0],1); Serial.println("% of factory value");
    Serial.print(F("y-axis self test: acceleration trim within : "));
    Serial.print(myIMU.selfTest[1],1); Serial.println("% of factory value");
    Serial.print(F("z-axis self test: acceleration trim within : "));
    Serial.print(myIMU.selfTest[2],1); Serial.println("% of factory value");
    Serial.print(F("x-axis self test: gyration trim within : "));
    Serial.print(myIMU.selfTest[3],1); Serial.println("% of factory value");
    Serial.print(F("y-axis self test: gyration trim within : "));
    Serial.print(myIMU.selfTest[4],1); Serial.println("% of factory value");
    Serial.print(F("z-axis self test: gyration trim within : "));
    Serial.print(myIMU.selfTest[5],1); Serial.println("% of factory value");

    // Calibrate gyro and accelerometers, load biases in bias registers
    myIMU.calibrateMPU9250(myIMU.gyroBias, myIMU.accelBias);

    myIMU.initMPU9250();
    // Initialize device for active mode read of acclerometer, gyroscope, and
    // temperature
    Serial.println("MPU9250 initialized for active data mode....");

    // Read the WHO_AM_I register of the magnetometer, this is a good test of
    // communication
    byte d = myIMU.readByte(AK8963_ADDRESS, WHO_AM_I_AK8963);
    Serial.print("AK8963 ");
    Serial.print("I AM 0x");
    Serial.print(d, HEX);
    Serial.print(" I should be 0x");
    Serial.println(0x48, HEX);

    if (d != 0x48)
    {
      // Communication failed, stop here
      Serial.println(F("Communication failed, abort!"));
      Serial.flush();
      abort();
    }

    // Get magnetometer calibration from AK8963 ROM
    myIMU.initAK8963(myIMU.factoryMagCalibration);
    // Initialize device for active mode read of magnetometer
    Serial.println("AK8963 initialized for active data mode....");

    if (SerialDebug)
    {
      //  Serial.println("Calibration values: ");
      Serial.print("X-Axis factory sensitivity adjustment value ");
      Serial.println(myIMU.factoryMagCalibration[0], 2);
      Serial.print("Y-Axis factory sensitivity adjustment value ");
      Serial.println(myIMU.factoryMagCalibration[1], 2);
      Serial.print("Z-Axis factory sensitivity adjustment value ");
      Serial.println(myIMU.factoryMagCalibration[2], 2);
    }

    // Get sensor resolutions, only need to do this once
    myIMU.getAres();
    myIMU.getGres();
    myIMU.getMres();

    // The next call delays for 4 seconds, and then records about 15 seconds of
    // data to calculate bias and scale.
//    myIMU.magCalMPU9250(myIMU.magBias, myIMU.magScale);
    Serial.println("AK8963 mag biases (mG)");
    Serial.println(myIMU.magBias[0]);
    Serial.println(myIMU.magBias[1]);
    Serial.println(myIMU.magBias[2]);

    Serial.println("AK8963 mag scale (mG)");
    Serial.println(myIMU.magScale[0]);
    Serial.println(myIMU.magScale[1]);
    Serial.println(myIMU.magScale[2]);
//    delay(2000); // Add delay to see results before serial spew of data

    if(SerialDebug)
    {
      Serial.println("Magnetometer:");
      Serial.print("X-Axis sensitivity adjustment value ");
      Serial.println(myIMU.factoryMagCalibration[0], 2);
      Serial.print("Y-Axis sensitivity adjustment value ");
      Serial.println(myIMU.factoryMagCalibration[1], 2);
      Serial.print("Z-Axis sensitivity adjustment value ");
      Serial.println(myIMU.factoryMagCalibration[2], 2);
    }
  } // if (c == 0x71)
  else
  {
    Serial.print("Could not connect to MPU9250: 0x");
    Serial.println(c, HEX);

    // Communication failed, stop here
    Serial.println(F("Communication failed, abort!"));
    Serial.flush();
    abort();
  }
}

void loop()
{
  // If intPin goes high, all data registers have new data
  // On interrupt, check if data ready interrupt
  if (myIMU.readByte(MPU9250_ADDRESS, INT_STATUS) & 0x01)
  {
    myIMU.readAccelData(myIMU.accelCount);  // Read the x/y/z adc values

    // Now we'll calculate the accleration value into actual g's
    // This depends on scale being set
    myIMU.ax = (float)myIMU.accelCount[0] * myIMU.aRes; // - myIMU.accelBias[0];
    myIMU.ay = (float)myIMU.accelCount[1] * myIMU.aRes; // - myIMU.accelBias[1];
    myIMU.az = (float)myIMU.accelCount[2] * myIMU.aRes; // - myIMU.accelBias[2];

    myIMU.readGyroData(myIMU.gyroCount);  // Read the x/y/z adc values

    // Calculate the gyro value into actual degrees per second
    // This depends on scale being set
    myIMU.gx = (float)myIMU.gyroCount[0] * myIMU.gRes;
    myIMU.gy = (float)myIMU.gyroCount[1] * myIMU.gRes;
    myIMU.gz = (float)myIMU.gyroCount[2] * myIMU.gRes;

    myIMU.readMagData(myIMU.magCount);  // Read the x/y/z adc values

    // Calculate the magnetometer values in milliGauss
    // Include factory calibration per data sheet and user environmental
    // corrections
    // Get actual magnetometer value, this depends on scale being set
    myIMU.mx = (float)myIMU.magCount[0] * myIMU.mRes
               * myIMU.factoryMagCalibration[0] - myIMU.magBias[0];
    myIMU.my = (float)myIMU.magCount[1] * myIMU.mRes
               * myIMU.factoryMagCalibration[1] - myIMU.magBias[1];
    myIMU.mz = (float)myIMU.magCount[2] * myIMU.mRes
               * myIMU.factoryMagCalibration[2] - myIMU.magBias[2];
  } // if (readByte(MPU9250_ADDRESS, INT_STATUS) & 0x01)

  // Must be called before updating quaternions!
  myIMU.updateTime();

  // Sensors x (y)-axis of the accelerometer is aligned with the y (x)-axis of
  // the magnetometer; the magnetometer z-axis (+ down) is opposite to z-axis
  // (+ up) of accelerometer and gyro! We have to make some allowance for this
  // orientationmismatch in feeding the output to the quaternion filter. For the
  // MPU-9250, we have chosen a magnetic rotation that keeps the sensor forward
  // along the x-axis just like in the LSM9DS0 sensor. This rotation can be
  // modified to allow any convenient orientation convention. This is ok by
  // aircraft orientation standards! Pass gyro rate as rad/s
  MahonyQuaternionUpdate(myIMU.ax, myIMU.ay, myIMU.az, myIMU.gx * DEG_TO_RAD,
                         myIMU.gy * DEG_TO_RAD, myIMU.gz * DEG_TO_RAD, myIMU.my,
                         myIMU.mx, myIMU.mz, myIMU.deltat);

  if (!AHRS)
  {
    myIMU.delt_t = millis() - myIMU.count;
    if (myIMU.delt_t > 500)
    {
      if(SerialDebug)
      {
        // Print acceleration values in milligs!
        Serial.print("X-acceleration: "); Serial.print(1000 * myIMU.ax);
        Serial.print(" mg ");
        Serial.print("Y-acceleration: "); Serial.print(1000 * myIMU.ay);
        Serial.print(" mg ");
        Serial.print("Z-acceleration: "); Serial.print(1000 * myIMU.az);
        Serial.println(" mg ");

        // Print gyro values in degree/sec
        Serial.print("X-gyro rate: "); Serial.print(myIMU.gx, 3);
        Serial.print(" degrees/sec ");
        Serial.print("Y-gyro rate: "); Serial.print(myIMU.gy, 3);
        Serial.print(" degrees/sec ");
        Serial.print("Z-gyro rate: "); Serial.print(myIMU.gz, 3);
        Serial.println(" degrees/sec");

        // Print mag values in degree/sec
        Serial.print("X-mag field: "); Serial.print(myIMU.mx);
        Serial.print(" mG ");
        Serial.print("Y-mag field: "); Serial.print(myIMU.my);
        Serial.print(" mG ");
        Serial.print("Z-mag field: "); Serial.print(myIMU.mz);
        Serial.println(" mG");

        myIMU.tempCount = myIMU.readTempData();  // Read the adc values
        // Temperature in degrees Centigrade
        myIMU.temperature = ((float) myIMU.tempCount) / 333.87 + 21.0;
        // Print temperature in degrees Centigrade
        Serial.print("Temperature is ");  Serial.print(myIMU.temperature, 1);
        Serial.println(" degrees C");
      }

      myIMU.count = millis();
      digitalWrite(myLed, !digitalRead(myLed));  // toggle led
    } // if (myIMU.delt_t > 500)
  } // if (!AHRS)
  else
  {
    // Serial print and/or display at 0.5 s rate independent of data rates
    myIMU.delt_t = millis() - myIMU.count;

    // update LCD once per half-second independent of read rate
    if (myIMU.delt_t > 500)
    {
      if(SerialDebug)
      {
        Serial.print("ax = ");  Serial.print((int)1000 * myIMU.ax);
        Serial.print(" ay = "); Serial.print((int)1000 * myIMU.ay);
        Serial.print(" az = "); Serial.print((int)1000 * myIMU.az);
        Serial.println(" mg");

        Serial.print("gx = ");  Serial.print(myIMU.gx, 2);
        Serial.print(" gy = "); Serial.print(myIMU.gy, 2);
        Serial.print(" gz = "); Serial.print(myIMU.gz, 2);
        Serial.println(" deg/s");

        Serial.print("mx = ");  Serial.print((int)myIMU.mx);
        Serial.print(" my = "); Serial.print((int)myIMU.my);
        Serial.print(" mz = "); Serial.print((int)myIMU.mz);
        Serial.println(" mG");

        Serial.print("q0 = ");  Serial.print(*getQ());
        Serial.print(" qx = "); Serial.print(*(getQ() + 1));
        Serial.print(" qy = "); Serial.print(*(getQ() + 2));
        Serial.print(" qz = "); Serial.println(*(getQ() + 3));
      }

// Define output variables from updated quaternion---these are Tait-Bryan
// angles, commonly used in aircraft orientation. In this coordinate system,
// the positive z-axis is down toward Earth. Yaw is the angle between Sensor
// x-axis and Earth magnetic North (or true North if corrected for local
// declination, looking down on the sensor positive yaw is counterclockwise.
// Pitch is angle between sensor x-axis and Earth ground plane, toward the
// Earth is positive, up toward the sky is negative. Roll is angle between
// sensor y-axis and Earth ground plane, y-axis up is positive roll. These
// arise from the definition of the homogeneous rotation matrix constructed
// from quaternions. Tait-Bryan angles as well as Euler angles are
// non-commutative; that is, the get the correct orientation the rotations
// must be applied in the correct order which for this configuration is yaw,
// pitch, and then roll.
// For more see
// http://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles
// which has additional links.
      myIMU.yaw   = atan2(2.0f * (*(getQ()+1) * *(getQ()+2) + *getQ()
                    * *(getQ()+3)), *getQ() * *getQ() + *(getQ()+1)
                    * *(getQ()+1) - *(getQ()+2) * *(getQ()+2) - *(getQ()+3)
                    * *(getQ()+3));
      myIMU.pitch = -asin(2.0f * (*(getQ()+1) * *(getQ()+3) - *getQ()
                    * *(getQ()+2)));
      myIMU.roll  = atan2(2.0f * (*getQ() * *(getQ()+1) + *(getQ()+2)
                    * *(getQ()+3)), *getQ() * *getQ() - *(getQ()+1)
                    * *(getQ()+1) - *(getQ()+2) * *(getQ()+2) + *(getQ()+3)
                    * *(getQ()+3));
      myIMU.pitch *= RAD_TO_DEG;
      myIMU.yaw   *= RAD_TO_DEG;

      // Declination of SparkFun Electronics (40°05'26.6"N 105°11'05.9"W) is
      //    8° 30' E  ± 0° 21' (or 8.5°) on 2016-07-19
      // - http://www.ngdc.noaa.gov/geomag-web/#declination
      myIMU.yaw  -= 8.5;
      myIMU.roll *= RAD_TO_DEG;

      if(SerialDebug)
      {
        Serial.print("Yaw, Pitch, Roll: ");
        Serial.print(myIMU.yaw, 2);
        Serial.print(", ");
        Serial.print(myIMU.pitch, 2);
        Serial.print(", ");
        Serial.println(myIMU.roll, 2);

        Serial.print("rate = ");
        Serial.print((float)myIMU.sumCount / myIMU.sum, 2);
        Serial.println(" Hz");
      }

      myIMU.count = millis();
      myIMU.sumCount = 0;
      myIMU.sum = 0;
    } // if (myIMU.delt_t > 500)
  } // if (AHRS)
}

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