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Topic: tilt compensate a compass (Read 941 times) previous topic - next topic


I have a digital compass, accelerometer and a gyroscope. I am trying to tilt compensate the compass so it continues to give readings when tilted.
how can I go about doing this?

code for accelerometer.
Code: [Select]
   Read the Memsic 2125 two-axis accelerometer.  Converts the
   pulses output by the 2125 into milli-g's (1/1000 of earth's
   gravity) and prints them over the serial connection to the
   The circuit:
* X output of accelerometer to digital pin 2
* Y output of accelerometer to digital pin 3
* +V of accelerometer to +5V
* GND of accelerometer to ground
   created 6 Nov 2008
   by David A. Mellis
   modified 30 Aug 2011
   by Tom Igoe
   This example code is in the public domain.


// these constants won't change:
const int xPin = 2; // X output of the accelerometer
const int yPin = 3; // Y output of the accelerometer

void setup() {
  // initialize serial communications:
  // initialize the pins connected to the accelerometer
  // as inputs:
  pinMode(xPin, INPUT);
  pinMode(yPin, INPUT);

void loop() {
  // variables to read the pulse widths:
  int pulseX, pulseY;
  // variables to contain the resulting accelerations
  int accelerationX, accelerationY;
  // read pulse from x- and y-axes:
  pulseX = pulseIn(xPin,HIGH); 
  pulseY = pulseIn(yPin,HIGH);
  // convert the pulse width into acceleration
  // accelerationX and accelerationY are in milli-g's:
  // earth's gravity is 1000 milli-g's, or 1g.
  accelerationX = ((pulseX / 10) - 500) * 8;
  accelerationY = ((pulseY / 10) - 500) * 8;

  // print the acceleration
  // print a tab character:


code for compass
Code: [Select]
#define HMC5883_WriteAddress 0x1E //  i.e 0x3C >> 1
#define HMC5883_ModeRegisterAddress 0x02
#define HMC5883_ContinuousModeCommand 0x00
#define HMC5883_DataOutputXMSBAddress  0x03

#include <Wire.h>

int regb=0x01;
int regbdata=0x40;
int outputData[6];

int pos = 0;    // variable to store the servo position

void setup()
    Wire.begin();       //Initiate the Wire library and join the I2C bus as a master
//  myservo.attach(9);  // attaches the servo on pin 9 to the servo object

void loop() {

    int i,x,y,z;
    double angle;
    Wire.beginTransmission(HMC5883_WriteAddress); //Initiate a transmission with HMC5883 (Write address).
    Wire.send(HMC5883_ModeRegisterAddress);       //Place the Mode Register Address in send-buffer.
    Wire.send(HMC5883_ContinuousModeCommand);     //Place the command for Continuous operation Mode in send-buffer.
    Wire.endTransmission();                       //Send the send-buffer to HMC5883 and end the I2C transmission.
    Wire.beginTransmission(HMC5883_WriteAddress);  //Initiate a transmission with HMC5883 (Write address).
    Wire.requestFrom(HMC5883_WriteAddress,6);      //Request 6 bytes of data from the address specified.
    if(6 <= Wire.available()) // If the number of bytes available for reading be <=6.
            outputData[i]=Wire.receive();  //Store the data in outputData buffer
    x=outputData[0] << 8 | outputData[1]; //Combine MSB and LSB of X Data output register
    z=outputData[2] << 8 | outputData[3]; //Combine MSB and LSB of Z Data output register
    y=outputData[4] << 8 | outputData[5]; //Combine MSB and LSB of Y Data output register
    angle= atan2((double)y,(double)x) * (180 / 3.14159265) + 180; // angle in degrees



All of my projects --> http://www.frankmagazu.com/


Dec 27, 2012, 01:48 pm Last Edit: Dec 27, 2012, 01:49 pm by AWOL Reason: 1
Tricky with a two axis accelerometer, I would have thought.

"tilt compensated compass algorithm" on Google only gave 434000 results
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.


google "sparkfun razor" and check out the example code they provide. it works like a charm. i assume you can modify it to fit your hardware setup.


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