The Start

Hi, What and Why

Plug it in

Rule number 1

Water Sensor

Sound Sensor


Tri Colour LED

RTC (Real Time Clock) DS1302

RTC (Real Time Clock) DS3231

Matrix LED step 1


Stepper Motor

LCD revisited with PCF8574T

Humidity Sensor

Shift Register

RFID tags (RC-522)

7 Segment display

Ultrasonic distance sensor

5V regulator

analogRead and analogWrite

Wiring an Array of Switches

The next step

Other things I have bought

Infra red and Processing

Programming a separate arduino chip

Creating your own PCB

L293D for a DC motor

4 digit 7 segment display

Starting with motors

RF433 Wireless Comms

Sort a character array

More stuff

I2C devices (SDA,SCL)

I2C scanner

SPI devices (MOSI,MISO)

HMC5883L Compass

MMA7361 Accelerometer

Added projects

Message Display System

4WD robot car
4WD robot car II

4WD robot car COMPLETE

MP3 Player

Compass HMC5883L

This is a 3 axis compass; It's an i2c device with an address of 0x1E.

Compass HMC5883L (badly wired up). 5V, GND, SCL to A5 and SDA to A4; ignore random cable colours. compass HMC5883L

This is the code that I used; it certainly seems to work, but I will be doing much work on the programming as it gets incorporated to me quadcopter project.

Useful info is here.

Looking at the output, I can see when to compass is rotated, my heading (in degrees) changes between 0 (North), 180 (South) and 360 (North), and all the compass points in between. At the moment, thats all I need to be confident of connecting it to my quadcopter and ensuring it consistently points in one direction.
The angle will also change as the quadcopter is tilted; my accelerometer is next, and should provide data to modify this compass reading during quad tilt.

HMC5883L_Example.pde - Example sketch for integration with an HMC5883L triple axis magnetomerwe.
Copyright (C) 2011 Love Electronics (

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 .


// 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.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:
  // Mine is: 2 N 37 W, which is 2.617 Degrees, or (which we need) 0.0456752665 radians, I will use 0.0457
  // MinePAUL is  -2 5' W
  // If you cannot find your Declination, comment out these two lines, your compass will be slightly off.
  // float declinationAngle = 0.0457;
  float declinationAngle = -0.04;
  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");