Pitch and roll angles from ADXL345

Projects Programming
1

How do you calculate the pitch and roll angles from the x, y and z from the ADXL345.

I have tried using this code from here http://www.den-uijl.nl/electronics/gyro.html

void loop() {
  timer = millis();
  getGyroscopeReadings(gyroResult);
  getAccelerometerReadings(accelResult);
  
  pitchAccel = atan2((accelResult[1] - biasAccelY) / 256, (accelResult[2] - biasAccelZ) / 256) * 360.0 / (2*PI);
  pitchGyro = pitchGyro + ((gyroResult[0] - biasGyroX) / 14.375) * timeStep;
  pitchPrediction = pitchPrediction + ((gyroResult[0] - biasGyroX) / 14.375) * timeStep;
  
  rollAccel = atan2((accelResult[0] - biasAccelX) / 256, (accelResult[2] - biasAccelZ) / 256) * 360.0 / (2*PI);
  rollGyro = rollGyro - ((gyroResult[1] - biasGyroY) / 14.375) * timeStep; 
  rollPrediction = rollPrediction - ((gyroResult[1] - biasGyroY) / 14.375) * timeStep;
  
  Pxx += timeStep * (2 * Pxv + timeStep * Pvv);
  Pxv += timeStep * Pvv;
  Pxx += timeStep * giroVar;
  Pvv += timeStep * deltaGiroVar;
  kx = Pxx * (1 / (Pxx + accelVar));
  kv = Pxv * (1 / (Pxx + accelVar));
  
  pitchPrediction += (pitchAccel - pitchPrediction) * kx;
  rollPrediction += (rollAccel - rollPrediction) * kx;
  
  Pxx *= (1 - kx);
  Pxv *= (1 - kx);
  Pvv -= kv * Pxv;
  
  Serial.print(pitchGyro);
  Serial.print("\t");
  Serial.print(pitchAccel);
  Serial.print("\t");
  Serial.print(pitchPrediction);
  Serial.print("\t"); 
  Serial.print(rollGyro);
  Serial.print("\t");
  Serial.print(rollAccel);
  Serial.print("\t");
  Serial.print(rollPrediction);
  Serial.print("\n");
  
  timer = millis() - timer;
  timer = (timeStep * 1000) - timer; 
  delay(timer);
}

But it doesn't seem to work - I am getting 0 or 1 for the angles.

Here is my code:

void Adafruit_ADXL345_Unified::getAngles(sensors_event_t &event, uint16_t &nPitchAngle, uint16_t &nRollAngle)
{
  float fPitch = 0.0, fRoll = 0.0;
  
  fPitch = atan2((event.acceleration.y - m_fZeroY) / 256, (event.acceleration.z - m_fZeroZ) / 256) * 360.0 / (2*PI);
  fRoll = atan2((event.acceleration.x - m_fZeroX) / 256, (event.acceleration.z - m_fZeroZ) / 256) * 360.0 / (2*PI);
   nPitchAngle = fPitch;
  nRollAngle = fRoll;
}
2

I have tried using this code

That won't even compile. The fine folks at http://snippets-r-us.com are experts at dealing with snippets.

3

PaulS:
That won't even compile. The fine folks at http://snippets-r-us.com are experts at dealing with snippets.

It is the calculations that I am concerned with here.

How do you calculate the roll and pitch from the raw data from the ADXL234?

Are the formulas used in that code snippet correct for the ADXL345?

4

It is the calculations that I am concerned with here.

So am I. But, I can't tell if you are performing integer arithmetic and expecting other than integer results.

How do you calculate the roll and pitch from the raw data from the ADXL234?

I don't. I don't need to.

Are the formulas used in that code snippet correct for the ADXL345?

Are you getting the right results? If not, then, clearly, the answer is no.

5

This is the definitive guide to pitch and roll calculations. Depending on sensor orientation, use either eqns 25 and 26, or 28 and 29.

Note: in the formula below, there is no need to divide by 256. atan2() takes care of the scaling.

atan2((accelResult[1] - biasAccelY) / 256, (accelResult[2] - biasAccelZ) / 256)
6

I found this website that explains it better:

http://theccontinuum.com/2012/09/24/arduino-imu-pitch-roll-from-accelerometer/