I have a HMC5883L on a GY271 break out board.
I'm running the test script in the HMC588L library:
/*
HMC5883L_Example.pde - Example sketch for integration with an HMC5883L triple axis magnetomerwe.
Copyright (C) 2011 Love Electronics (loveelectronics.co.uk)
This program is free software: you can redistribute it and/or modify
it under the terms of the version 3 GNU General Public License as
published by the Free Software Foundation.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
// Reference the I2C Library
#include <Wire.h>
// Reference the HMC5883L Compass Library
#include <HMC5883L.h>
// Store our compass as a variable.
HMC5883L compass;
// Record any errors that may occur in the compass.
int error = 0;
// Out setup routine, here we will configure the microcontroller and compass.
void setup()
{
// Initialize the serial port.
Serial.begin(9600);
Serial.println("Starting the I2C interface.");
Wire.begin(); // Start the I2C interface.
Serial.println("Constructing new HMC5883L");
compass = HMC5883L(); // Construct a new HMC5883 compass.
Serial.println("Setting scale to +/- 1.3 Ga");
error = compass.SetScale(1.3); // Set the scale of the compass.
if(error != 0) // If there is an error, print it out.
Serial.println(compass.GetErrorText(error));
Serial.println("Setting measurement mode to continous.");
error = compass.SetMeasurementMode(Measurement_Continuous); // Set the measurement mode to Continuous
if(error != 0) // If there is an error, print it out.
Serial.println(compass.GetErrorText(error));
}
// Our main program loop.
void loop()
{
// Retrive the raw values from the compass (not scaled).
MagnetometerRaw raw = compass.ReadRawAxis();
// Retrived the scaled values from the compass (scaled to the configured scale).
MagnetometerScaled scaled = compass.ReadScaledAxis();
// Values are accessed like so:
int MilliGauss_OnThe_XAxis = scaled.XAxis;// (or YAxis, or ZAxis)
// Calculate heading when the magnetometer is level, then correct for signs of axis.
float heading = atan2(scaled.YAxis, scaled.XAxis);
// Once you have your heading, you must then add your 'Declination Angle', which is the 'Error' of the magnetic field in your location.
// Find yours here: http://www.magnetic-declination.com/
// Mine is: 2� 37' W, which is 2.617 Degrees, or (which we need) 0.0456752665 radians, I will use 0.0457
// If you cannot find your Declination, comment out these two lines, your compass will be slightly off.
//float declinationAngle = 0.0457;
//eading += declinationAngle;
// Correct for when signs are reversed.
if(heading < 0)
heading += 2*PI;
// Check for wrap due to addition of declination.
if(heading > 2*PI)
heading -= 2*PI;
// Convert radians to degrees for readability.
float headingDegrees = heading * 180/M_PI;
// Output the data via the serial port.
Output(raw, scaled, heading, headingDegrees);
// Normally we would delay the application by 66ms to allow the loop
// to run at 15Hz (default bandwidth for the HMC5883L).
// However since we have a long serial out (104ms at 9600) we will let
// it run at its natural speed.
// delay(66);
}
// Output the data down the serial port.
void Output(MagnetometerRaw raw, MagnetometerScaled scaled, float heading, float headingDegrees)
{
Serial.print("Raw:\t");
Serial.print(raw.XAxis);
Serial.print(" ");
Serial.print(raw.YAxis);
Serial.print(" ");
Serial.print(raw.ZAxis);
Serial.print(" \tScaled:\t");
Serial.print(scaled.XAxis);
Serial.print(" ");
Serial.print(scaled.YAxis);
Serial.print(" ");
Serial.print(scaled.ZAxis);
Serial.print(" \tHeading:\t");
Serial.print(heading);
Serial.print(" Radians \t");
Serial.print(headingDegrees);
Serial.println(" Degrees \t");
}
It's not working though, the values fluctuate with motion, I've included a sample here as the sensor is rotated.
HeadingúStarting the I2C interface.
Constructing new HMC5883L
Setting scale to +/- 1.3 Ga
Setting measurement mode to continous.
Raw: 557 165 -265 Scaled: 512.44 151.80 -243.80 Heading: 0.29 Radians 16.50 Degrees
Raw: 557 165 -265 Scaled: 512.44 151.80 -243.80 Heading: 0.29 Radians 16.50 Degrees
Raw: 558 163 -264 Scaled: 513.36 149.96 -242.88 Heading: 0.28 Radians 16.28 Degrees
Raw: 539 56 -277 Scaled: 495.88 51.52 -254.84 Heading: 0.10 Radians 5.93 Degrees
Raw: 565 -23 -230 Scaled: 519.80 -21.16 -211.60 Heading: 6.24 Radians 357.67 Degrees
Raw: 556 -20 -194 Scaled: 511.52 -18.40 -178.48 Heading: 6.25 Radians 357.94 Degrees
Raw: 520 5 -194 Scaled: 478.40 4.60 -178.48 Heading: 0.01 Radians 0.55 Degrees
Raw: 495 -2 -191 Scaled: 455.40 -1.84 -175.72 Heading: 6.28 Radians 359.77 Degrees
Raw: 487 -53 -182 Scaled: 448.04 -48.76 -167.44 Heading: 6.17 Radians 353.79 Degrees
Raw: 435 -115 -167 Scaled: 400.20 -105.80 -153.64 Heading: 6.02 Radians 345.19 Degrees
Raw: 428 -87 -174 Scaled: 393.76 -80.04 -160.08 Heading: 6.08 Radians 348.51 Degrees
Raw: 380 -42 -169 Scaled: 349.60 -38.64 -155.48 Heading: 6.17 Radians 353.69 Degrees
Raw: 388 -23 -176 Scaled: 356.96 -21.16 -161.92 Heading: 6.22 Radians 356.61 Degrees
Raw: 356 2 -164 Scaled: 327.52 1.84 -150.88 Heading: 0.01 Radians 0.32 Degrees
Raw: 346 26 -158 Scaled: 318.32 35.88 -143.52 Heading: 0.11 Radians 6.43 Degrees
Raw: 351 59 -158 Scaled: 322.92 54.28 -145.36 Heading: 0.17 Radians 9.54 Degrees
Raw: 351 82 -158 Scaled: 322.92 75.44 -145.36 Heading: 0.23 Radians 13.15 Degrees
Raw: 353 94 -155 Scaled: 324.76 86.48 -142.60 Heading: 0.26 Radians 14.91 Degrees
Raw: 360 113 -153 Scaled: 331.20 103.96 -140.76 Heading: 0.30 Radians 17.43 Degrees
Raw: 374 124 -153 Scaled: 344.08 114.08 -140.76 Heading: 0.32 Radians 18.34 Degrees
Raw: 335 120 -146 Scaled: 308.20 110.40 -134.32 Heading: 0.34 Radians 19.71 Degrees
Raw: 296 141 -127 Scaled: 272.32 129.72 -116.84 Heading: 0.44 Radians 25.47 Degrees
Raw: 291 170 -121 Scaled: 267.72 156.40 -111.32 Heading: 0.53 Radians 30.29 Degrees
Raw: 293 187 -114 Scaled: 269.56 172.04 -104.88 Heading: 0.57 Radians 32.55 Degrees
Raw: 305 217 -107 Scaled: 280.60 199.64 -98.44 Heading: 0.62 Radians 35.43 Degrees
Raw: 317 260 -96 Scaled: 291.64 239.20 -88.32 Heading: 0.69 Radians 39.36 Degrees
Raw: 499 325 -82 Scaled: 459.08 299.00 -75.44 Heading: 0.58 Radians 33.08 Degrees
Raw: 578 304 -78 Scaled: 531.76 279.68 -71.76 Heading: 0.48 Radians 27.74 Degrees
Raw: 595 290 -83 Scaled: 547.40 266.80 -76.36 Heading: 0.45 Radians 25.98 Degrees
Raw: 646 238 -88 Scaled: 594.32 218.96 -80.96 Heading: 0.35 Radians 20.22 Degrees
Raw: 668 213 -89 Scaled: 614.56 195.96 -81.88 Heading: 0.31 Radians 17.69 Degrees
Raw: 662 194 -101 Scaled: 609.04 178.48 -92.92 Heading: 0.29 Radians 16.33 Degrees
Raw: 673 156 -107 Scaled: 619.16 143.52 -98.44 Heading: 0.23 Radians 13.05 Degrees
Raw: 689 122 -108 Scaled: 633.88 112.24 -99.36 Heading: 0.18 Radians 10.04 Degrees
Raw: 651 66 -137 Scaled: 598.92 60.72 -126.04 Heading: 0.10 Radians 5.79 Degrees
Raw: 637 40 -146 Scaled: 586.04 36.80 -134.32 Heading: 0.06 Radians 3.59 Degrees
Raw: 613 -9 -153 Scaled: 563.96 -8.28 -140.76 Heading: 6.27 Radians 359.16 Degrees
Raw: 556 -88 -160 Scaled: 511.52 -80.96 -147.20 Heading: 6.13 Radians 351.01 Degrees
The heading values fluctuate approximately from 350 -> 360 and between 10 and 30 degrees but never anything outside of this. It appears that the x value (col one above) never becomes negative (you would expect it be be negative for 50% of the time) assuming an even rotation.
Has anyone seen this behaviour before? Can anyone think of why this might happen?