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I have an Adafruit LSM303 accelerometer and compass attached to an Arduino Uno.

I used one of Adafruit's recommended calibration sketches (see below) and got the following output:

  • Accel Minimums: -8.55 -10.16 -14.12
  • Accel Maximums: 9.89 11.26 15.26
  • Mag Minimums: -60.09 -57.55 -130.51
  • Mag Maximums: 69.64 78.09 68.88

How do I take the calibration output and use it to calibrate the compass using Adafruit's recommended code?

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_LSM303_U.h>

/* Assign a unique ID to these sensors */
Adafruit_LSM303_Accel_Unified accel = Adafruit_LSM303_Accel_Unified(54321);
Adafruit_LSM303_Mag_Unified mag = Adafruit_LSM303_Mag_Unified(12345);

float AccelMinX, AccelMaxX;
float AccelMinY, AccelMaxY;
float AccelMinZ, AccelMaxZ;

float MagMinX, MagMaxX;
float MagMinY, MagMaxY;
float MagMinZ, MagMaxZ;

long lastDisplayTime;

void setup(void) 
{
  Serial.begin(9600);
  Serial.println("LSM303 Calibration"); Serial.println("");

  /* Initialise the accelerometer */
  if(!accel.begin())
  {
    /* There was a problem detecting the ADXL345 ... check your connections */
    Serial.println("Ooops, no LSM303 detected ... Check your wiring!");
    while(1);
  }
  /* Initialise the magnetometer */
  if(!mag.begin())
  {
    /* There was a problem detecting the LSM303 ... check your connections */
    Serial.println("Ooops, no LSM303 detected ... Check your wiring!");
    while(1);
  }
  lastDisplayTime = millis();
}

void loop(void) 
{
  /* Get a new sensor event */ 
  sensors_event_t accelEvent; 
  sensors_event_t magEvent; 

  accel.getEvent(&accelEvent);
  mag.getEvent(&magEvent);

  if (accelEvent.acceleration.x < AccelMinX) AccelMinX = accelEvent.acceleration.x;
  if (accelEvent.acceleration.x > AccelMaxX) AccelMaxX = accelEvent.acceleration.x;

  if (accelEvent.acceleration.y < AccelMinY) AccelMinY = accelEvent.acceleration.y;
  if (accelEvent.acceleration.y > AccelMaxY) AccelMaxY = accelEvent.acceleration.y;

  if (accelEvent.acceleration.z < AccelMinZ) AccelMinZ = accelEvent.acceleration.z;
  if (accelEvent.acceleration.z > AccelMaxZ) AccelMaxZ = accelEvent.acceleration.z;

  if (magEvent.magnetic.x < MagMinX) MagMinX = magEvent.magnetic.x;
  if (magEvent.magnetic.x > MagMaxX) MagMaxX = magEvent.magnetic.x;

  if (magEvent.magnetic.y < MagMinY) MagMinY = magEvent.magnetic.y;
  if (magEvent.magnetic.y > MagMaxY) MagMaxY = magEvent.magnetic.y;

  if (magEvent.magnetic.z < MagMinZ) MagMinZ = magEvent.magnetic.z;
  if (magEvent.magnetic.z > MagMaxZ) MagMaxZ = magEvent.magnetic.z;

  if ((millis() - lastDisplayTime) > 1000)  // display once/second
  {
    Serial.print("Accel Minimums: "); Serial.print(AccelMinX); Serial.print("  ");Serial.print(AccelMinY); Serial.print("  "); Serial.print(AccelMinZ); Serial.println();
    Serial.print("Accel Maximums: "); Serial.print(AccelMaxX); Serial.print("  ");Serial.print(AccelMaxY); Serial.print("  "); Serial.print(AccelMaxZ); Serial.println();
    Serial.print("Mag Minimums: "); Serial.print(MagMinX); Serial.print("  ");Serial.print(MagMinY); Serial.print("  "); Serial.print(MagMinZ); Serial.println();
    Serial.print("Mag Maximums: "); Serial.print(MagMaxX); Serial.print("  ");Serial.print(MagMaxY); Serial.print("  "); Serial.print(MagMaxZ); Serial.println(); Serial.println();
    lastDisplayTime = millis();
  }
}
user8012080
  • 23
  • 3

1 Answers1

0

On the adafruit page you linked to, it says "we can use the atan2() function to compute the angle of the vector defined by the Y and X axis readings" I also found instruction from Honeywell regarding how to calculate compass heading when given a 3-axis magnetometer reading, and it corroborates that the formula should be as follows for the code above:

float magFieldRad = atan2(magEvent.magnetic.x, magEvent.magnetic.y); // compass in Radians
float magFieldDeg = (magFieldRad * 180) / 3.1415; // compass in Degrees
Blake
  • 43
  • 5