File content as of revision 2:ba7945a8d1c6:

#include "mbed.h"
#include "MPU6050.h"

/*
 Hardware setup:
 MPU6050 Breakout --------- Arduino
 3.3V --------------------- 3.3V
 SDA ----------------------- A4
 SCL ----------------------- A5
 GND ---------------------- GND
 
  Note: The MPU6050 is an I2C sensor and uses the Arduino Wire library. 
 Because the sensor is not 5V tolerant, we are using a 3.3 V 8 MHz Pro Mini or a 3.3 V Teensy 3.1.
 We have disabled the internal pull-ups used by the Wire library in the Wire.h/twi.c utility file.
 We are also using the 400 kHz fast I2C mode by setting the TWI_FREQ  to 400000L /twi.h utility file.
*/

MPU6050 mpu6050;
Timer t;
Serial pc(USBTX, USBRX); // tx, rx
float sum = 0;
uint32_t sumCount = 0;

void main ()
{
    pc.baud(9600);  

    //Set up I2C
    i2c.frequency(400000);  // use fast (400 kHz) I2C   
  
    t.start();
    // Read the WHO_AM_I register, this is a good test of communication
    uint8_t whoami = mpu6050.readByte(MPU6050_ADDRESS, WHO_AM_I_MPU6050);  // Read WHO_AM_I register for MPU-6050
    pc.printf("I AM 0x%x\n", whoami); 
    pc.printf("I SHOULD BE 0x68\n");
    
    if (whoami == 0x68) // WHO_AM_I should always be 0x68
    {
        pc.printf("MPU6050 is online")
        wait(1);
        mpu6050.MPU6050SelfTest(SelfTest); // Start by performing self test and reporting values
        pc.printf("x-axis self test: acceleration trim within : "); pc.printf("%f", SelfTest[0]); pc.printf("% of factory value \n\r");
        pc.printf("y-axis self test: acceleration trim within : "); pc.printf("%f", SelfTest[1]); pc.printf("% of factory value \n\r");
        pc.printf("z-axis self test: acceleration trim within : "); pc.printf("%f", SelfTest[2]); pc.printf("% of factory value \n\r");
        pc.printf("x-axis self test: gyration trim within : "); pc.printf("%f", SelfTest[3]); pc.printf("% of factory value \n\r");
        pc.printf("y-axis self test: gyration trim within : "); pc.printf("%f", SelfTest[4]); pc.printf("% of factory value \n\r");
        pc.printf("z-axis self test: gyration trim within : "); pc.printf("%f", SelfTest[5]); pc.printf("% of factory value \n\r");
        wait(1);
        if(SelfTest[0] < 1.0f && SelfTest[1] < 1.0f && SelfTest[2] < 1.0f && SelfTest[3] < 1.0f && SelfTest[4] < 1.0f && SelfTest[5] < 1.0f) 
        {
            mpu6050.resetMPU6050(); // Reset registers to default in preparation for device calibration
            mpu6050.calibrateMPU6050(gyroBias, accelBias); // Calibrate gyro and accelerometers, load biases in bias registers  
            mpu6050.initMPU6050(); pc.printf("MPU6050 initialized for active data mode....\n\r"); // Initialize device for active mode read of acclerometer, gyroscope, and temperature 
            wait(2);
        }
        else
        {
            pc.printf("Device did not the pass self-test!\n");
        }
    }
    else
    {
        pc.printf("Could not connect to MPU6050: \n");
        pc.printf("%#x \n",  whoami);
        while(true) ; // Loop forever if communication doesn't happen
    }
    while(true) {
    // If data ready bit set, all data registers have new data
      if(mpu6050.readByte(MPU6050_ADDRESS, INT_STATUS) & 0x01) // check if data ready interrupt
      {  
        mpu6050.readAccelData(accelCount);  // Read the x/y/z adc values
        mpu6050.getAres();
        
        // Now we'll calculate the accleration value into actual g's
        ax = (float)accelCount[0]*aRes - accelBias[0];  // get actual g value, this depends on scale being set
        ay = (float)accelCount[1]*aRes - accelBias[1];   
        az = (float)accelCount[2]*aRes - accelBias[2];  
        
        mpu6050.readGyroData(gyroCount);  // Read the x/y/z adc values
        mpu6050.getGres();
        
        // Calculate the gyro value into actual degrees per second
        gx = (float)gyroCount[0]*gRes; // - gyroBias[0];  // get actual gyro value, this depends on scale being set
        gy = (float)gyroCount[1]*gRes; // - gyroBias[1];  
        gz = (float)gyroCount[2]*gRes; // - gyroBias[2];   
        
        tempCount = mpu6050.readTempData();  // Read the x/y/z adc values
        temperature = (tempCount) / 340. + 36.53; // Temperature in degrees Centigrade
        }
        Now = t.read_us();
        deltat = (float)((Now - lastUpdate)/1000000.0f) ; // set integration time by time elapsed since last filter update
        lastUpdate = Now;
        
        sum += deltat;
        sumCount++;
        
        if(lastUpdate - firstUpdate > 10000000.0f) {
             beta = 0.04;  // decrease filter gain after stabilized
             zeta = 0.015; // increasey bias drift gain after stabilized
        }
        
        mpu6050.MadgwickQuaternionUpdate(ax, ay, az, gx*PI/180.0f, gy*PI/180.0f, gz*PI/180.0f);
        // Serial print and/or display at 0.5 s rate independent of data rates
        delt_t = t.read_ms() - count;
        
        if (delt_t > 500) // update once per half-second independent of read rate
        {
            /*
            pc.printf("ax = %f", 1000*ax); 
            pc.printf(" ay = %f", 1000*ay); 
            pc.printf(" az = %f  mg\n\r", 1000*az); 
        
            pc.printf("gx = %f", gx); 
            pc.printf(" gy = %f", gy); 
            pc.printf(" gz = %f  deg/s\n\r", gz); 
            
            pc.printf(" temperature = %f  C\n\r", temperature); 
            
            pc.printf("q0 = %f\n\r", q[0]);
            pc.printf("q1 = %f\n\r", q[1]);
            pc.printf("q2 = %f\n\r", q[2]);
            pc.printf("q3 = %f\n\r", q[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.
            yaw   = atan2(2.0f * (q[1] * q[2] + q[0] * q[3]), q[0] * q[0] + q[1] * q[1] - q[2] * q[2] - q[3] * q[3]);   
            pitch = -asin(2.0f * (q[1] * q[3] - q[0] * q[2]));
            roll  = atan2(2.0f * (q[0] * q[1] + q[2] * q[3]), q[0] * q[0] - q[1] * q[1] - q[2] * q[2] + q[3] * q[3]);
            pitch *= 180.0f / PI;
            yaw   *= 180.0f / PI; 
            roll  *= 180.0f / PI;
            //  pc.printf("Yaw, Pitch, Roll: \n\r");
            //  pc.printf("%f", yaw);
            //  pc.printf(", ");
            //  pc.printf("%f", pitch);
            //  pc.printf(", ");
            //  pc.printf("%f\n\r", roll);
            //  pc.printf("average rate = "); pc.printf("%f", (sumCount/sum)); pc.printf(" Hz\n\r");
        
            pc.printf("X, Y, Z, Yaw, Pitch, Roll: %f %f %f %f %f %f\n\r", gx, gy, gz, yaw, pitch, roll);
            //pc.printf("average rate = %f\n\r", (float) sumCount/sum);
         
            count = t.read_ms(); 
            sum = 0;
            sumCount = 0; 
        }
    }
}