ADXL335Calibration.ino

// Calibration Sketch for the ADXL335 
// For use with calibration instructions found at:
//   http://codergirljp.blogspot.com/2014/05/adxl335-accelerometer-on-teensy-31.html
//
// Modified from instructions found https://learn.adafruit.com/adafruit-analog-accelerometer-breakouts/programming 
// to run on the Teensy 3.1 without requiring any additional hardware setup
//
// Uses the Arduino Serial Monitor to trigger calibrations
// Runs a calibration each time it receives a "1" from the USB serial 
// The calibration should be performed with the accelerometer rotated to min and max positions for each Axis
// - calibrations for the same Axis can be repeated
// - Results for each calibration are retained through the entire calibration procedure
// - Mix/Max Values of 512 indicate that an axis has not been calibrated.

// Teensy 3.1 Analog pins for the X, Y, Z outputs of the Accelerometer
const int xInput = 0;
const int yInput = 1;
const int zInput = 2;

// Raw Ranges:
// initialize to mid-range and allow calibration to
// find the minimum and maximum for each axis
int xRawMin = 512;
int xRawMax = 512;
 
int yRawMin = 512;
int yRawMax = 512;
 
int zRawMin = 512;
int zRawMax = 512;
 
 
// Take multiple samples
const int sampleSize = 10;
 

void setup() 
{
  Serial.begin(38400);
}
 
void loop() 
{
  
   char startByte = '0';
   if (Serial.available() > 0) 
   {
                // read the byte
                startByte = Serial.read();
                Serial.print("Begin Calibration - received ");
                Serial.println(startByte);
   }
  
  if((int)startByte == '1')
  {
    delay(250);
    int xRaw = ReadAxis(xInput);
    int yRaw = ReadAxis(yInput);
    int zRaw = ReadAxis(zInput);
  
    AutoCalibrate(xRaw, yRaw, zRaw);

    Serial.print("Raw Ranges: X: ");
    Serial.print(xRawMin);
    Serial.print("-");
    Serial.print(xRawMax);
    
    Serial.print(", Y: ");
    Serial.print(yRawMin);
    Serial.print("-");
    Serial.print(yRawMax);
    
    Serial.print(", Z: ");
    Serial.print(zRawMin);
    Serial.print("-");
    Serial.print(zRawMax);
    Serial.println();
    Serial.print(xRaw);
    Serial.print(", ");
    Serial.print(yRaw);
    Serial.print(", ");
    Serial.print(zRaw);
    
    // Convert raw values to 'milli-Gs"
    long xScaled = map(xRaw, xRawMin, xRawMax, -1000, 1000);
    long yScaled = map(yRaw, yRawMin, yRawMax, -1000, 1000);
    long zScaled = map(zRaw, zRawMin, zRawMax, -1000, 1000);
  
    // re-scale to fractional Gs
    float xAccel = xScaled / 1000.0;
    float yAccel = yScaled / 1000.0;
    float zAccel = zScaled / 1000.0;
  
    Serial.print(" :: ");
    Serial.print(xAccel);
    Serial.print("G, ");
    Serial.print(yAccel);
    Serial.print("G, ");
    Serial.print(zAccel);
    Serial.println("G");
    
    //reset the startByte
    startByte = '0';
  }
}
 
//
// Read "sampleSize" samples and report the average
//
int ReadAxis(int axisPin)
{
  long reading = 0;
  analogRead(axisPin);
  delay(1);
  for (int i = 0; i < sampleSize; i++)
  {
    reading += analogRead(axisPin);
  }
  return reading/sampleSize;
}
 
//
// Find the extreme raw readings from each axis
//
void AutoCalibrate(int xRaw, int yRaw, int zRaw)
{
  Serial.println("Calibrate");
  if (xRaw < xRawMin)
  {
    xRawMin = xRaw;
  }
  if (xRaw > xRawMax)
  {
    xRawMax = xRaw;
  }
  
  if (yRaw < yRawMin)
  {
    yRawMin = yRaw;
  }
  if (yRaw > yRawMax)
  {
    yRawMax = yRaw;
  }
 
  if (zRaw < zRawMin)
  {
    zRawMin = zRaw;
  }
  if (zRaw > zRawMax)
  {
    zRawMax = zRaw;
  }
}