I am using the inbuilt compass of the BN-880 GPS Module. I have used the Adafruit code to get readings, and have put in my declination angle. However, the readings are completely off from the compass angles shown on an iphone. I thought this was a calibration error, so I created a table with all the readings.
However, when I checked again today, the numbers are off by +/- 20 degrees. How can I calibrate this, and am I doing something wrong with this code?
/***************************************************************************
This is a library example for the HMC5883 magnentometer/compass
Designed specifically to work with the Adafruit HMC5883 Breakout
http://www.adafruit.com/products/1746
*** You will also need to install the Adafruit_Sensor library! ***
These displays use I2C to communicate, 2 pins are required to interface.
Adafruit invests time and resources providing this open source code,
please support Adafruit andopen-source hardware by purchasing products
from Adafruit!
Written by Kevin Townsend for Adafruit Industries with some heading example from
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/>.
***************************************************************************/
#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_HMC5883_U.h>
/* Assign a unique ID to this sensor at the same time */
Adafruit_HMC5883_Unified mag = Adafruit_HMC5883_Unified(12345);
void displaySensorDetails(void)
{
sensor_t sensor;
mag.getSensor(&sensor);
Serial.println("------------------------------------");
Serial.print ("Sensor: "); Serial.println(sensor.name);
Serial.print ("Driver Ver: "); Serial.println(sensor.version);
Serial.print ("Unique ID: "); Serial.println(sensor.sensor_id);
Serial.print ("Max Value: "); Serial.print(sensor.max_value); Serial.println(" uT");
Serial.print ("Min Value: "); Serial.print(sensor.min_value); Serial.println(" uT");
Serial.print ("Resolution: "); Serial.print(sensor.resolution); Serial.println(" uT");
Serial.println("------------------------------------");
Serial.println("");
delay(500);
}
void setup(void)
{
Serial.begin(9600);
Serial.println("HMC5883 Magnetometer Test"); Serial.println("");
/* Initialise the sensor */
if(!mag.begin())
{
/* There was a problem detecting the HMC5883 ... check your connections */
Serial.println("Ooops, no HMC5883 detected ... Check your wiring!");
while(1);
}
/* Display some basic information on this sensor */
displaySensorDetails();
}
void loop(void)
{
/* Get a new sensor event */
sensors_event_t event;
mag.getEvent(&event);
/* Display the results (magnetic vector values are in micro-Tesla (uT)) */
Serial.print("X: "); Serial.print(event.magnetic.x); Serial.print(" ");
Serial.print("Y: "); Serial.print(event.magnetic.y); Serial.print(" ");
Serial.print("Z: "); Serial.print(event.magnetic.z); Serial.print(" ");Serial.println("uT");
// Hold the module so that Z is pointing 'up' and you can measure the heading with x&y
// Calculate heading when the magnetometer is level, then correct for signs of axis.
float heading = atan2(event.magnetic.y, event.magnetic.x);
// 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: -13* 2' W, which is ~13 Degrees, or (which we need) 0.22 radians
// If you cannot find your Declination, comment out these two lines, your compass will be slightly off.
float declinationAngle = 0.226311026;
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;
Serial.print("Heading (degrees): "); Serial.println(headingDegrees);
delay(500);
}