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Topic: HMC5883L magnetometer problem (Read 1 time) previous topic - next topic


Feb 20, 2013, 01:00 am Last Edit: Feb 20, 2013, 01:03 am by aen3 Reason: 1
Hey I'm having a problem with my HMC5883L sainsmart breakout board where I only get degree values between 139 and 155.  I have it mounted vertically and thus I changed this: float heading = atan2(scaled.YAxis, scaled.XAxis);   to this:   float heading = atan2(scaled.ZAxis, scaled.XAxis);

I ordered another one thinking that I had damaged the module but I am having the same problem.  I had it working before and I cant seem to figure out what is different.  The example code is below.  I also get the error "Entered scale was not valid, valid gauss values are: 0.88, 1.3, 1.9, 2.5, 4.0, 4.7, 5.6, 8.1" even though it is set to 1.3.

Code: [Select]
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
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.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("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.

// 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.ZAxis, 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;
 heading += 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("   ");  
  Serial.print("   ");  
  Serial.print("   \tScaled:\t");
  Serial.print("   ");  
  Serial.print("   ");  

  Serial.print("   \tHeading:\t");
  Serial.print(" Radians   \t");
  Serial.println(" Degrees   \t");



Code: [Select]
HMC5883L compass;
u get a fresh instance of HMC5883L.

And here in setup()
Code: [Select]
 Serial.println("Constructing new HMC5883L");
compass = HMC5883L(); // Construct a new HMC5883 compass.

u overwrite it with a second instance.

I think now u have 2 instances that deal with the same chip...

Did u try to test ur chip again without ur software changes?



That is the example that comes with the hmc5883l library. The first instance is a declaration that is needed. The only change I made was from y,x axis to z, x axis but I have tried every other combination.


I also get the error "Entered scale was not valid, valid gauss values are: 0.88, 1.3, 1.9, 2.5, 4.0, 4.7, 5.6, 8.1" even though it is set to 1.3.

That is a bug in the library.
Code: [Select]

char* HMC5883L::GetErrorText(int errorCode)
if(errorCode == ErrorCode_1_Num)
return ErrorCode_1;

return "Error not defined.";


Have you experienced the same issue where the bearing only changes minimally when rotating 360 degrees?

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