compass

 //compass


  if (millis() - throttle > 500) {
    throttle = millis();
    sensors_event_t event;
    accel.getEvent(&event);

    /* Display the results (acceleration is measured in m/s^2) */

    if (accelerometer_x > accelerometer_x + 1 || event.acceleration.x < accelerometer_x - 1) {
      accelerometer_x = accelerometer_x;
      Serial.print("accelerometer_x:");
      Serial.println(event.acceleration.x);
    }
    if (accelerometer_y > accelerometer_y + 1 || event.acceleration.y < accelerometer_y - 1) {
      accelerometer_y = accelerometer_y;
      Serial.print("accelerometer_y:");
      Serial.println(event.acceleration.y);
    }
    if (accelerometer_z > accelerometer_z + 1 || event.acceleration.x < accelerometer_z - 1) {
      accelerometer_z = accelerometer_z;
      Serial.print("accelerometer_z:");
      Serial.println(event.acceleration.z);
    }


    float Pi = 3.14159;

    // Calculate the angle of the vector y,x
    float heading = (atan2(event.magnetic.y, event.magnetic.x) * 180) / Pi;

    // Normalize to 0-360
    if (heading < 0)
    {
      heading = 360 + heading;
    }

    if (heading > lastHeading + 3 || heading < lastHeading - 3) {
      lastHeading = heading;

      Serial.print("compass_heading:");
      Serial.println(heading);
    }

  }
}