The Code

#include <Wire.h>
#include <Adafruit_NeoPixel.h>

// Used Pins on the Arduino
#define PIN 6
#define SCL 5 // Analog A5
#define SDA 4 // Analog A4

// Configure NeoPixel ring of 12 Leds
#define LEDS 12
Adafruit_NeoPixel strip = Adafruit_NeoPixel(LEDS, PIN, NEO_GRB + NEO_KHZ800);

// Configure HMC6352 digital compass via I2C
int HMC6352ReadAddress = 0x41;
int HMC6352SlaveAddress = 0x42;

void setup(){
Serial.begin(9600);

// “The Wire library uses 7 bit addresses throughout.
// If you have a datasheet or sample code that uses 8 bit address,
// you’ll want to drop the low bit (i.e. shift the value one bit to the right),
// yielding an address between 0 and 127.”
// I know 0x42 is less than 127, but this is still required
HMC6352SlaveAddress = HMC6352SlaveAddress >> 1;
Wire.begin();

strip.begin();
strip.show(); // Initialize all pixels to ‘off’
theaterChase(strip.Color(32, 32, 32), 50);
}

void loop(){
// Get Data from digital compass
Wire.beginTransmission(HMC6352SlaveAddress);
Wire.write(HMC6352ReadAddress); // The “Get Data” command
Wire.endTransmission();

// Time delays required by HMC6352 upon receipt of the command
// “Get Data”. Compensate and calculate new heading : 6ms
delay(6);

// Get the two data bytes, MSB and LSB
Wire.requestFrom(HMC6352SlaveAddress, 2);

// The heading output data will be the value in tenths of degrees
// from zero to 3599 and provided in binary format over the two bytes.
byte MSB = Wire.read();
byte LSB = Wire.read();

float headingSum = (MSB << 8) + LSB; //(MSB / LSB sum)
float headingInt = headingSum / 10;

Serial.println(headingSum/10.0);

// Map heading to the LEDS length of led ring
// Find N(orth) and S(outh)
float minSweep = 0;
float sweepRange = LEDS – minSweep;
int N = (int)(sweepRange – (headingInt / 360 * sweepRange) + minSweep);
int S = N + (LEDS/2); S = ( S > LEDS ) ? S – LEDS : S;

// Display the red north and green south led dot on the ring
strip.setPixelColor(N,strip.Color(32,0,0));strip.show();
strip.setPixelColor(S,strip.Color(0,16,0));strip.show();
delay(6);
strip.setPixelColor(N,strip.Color(0,0,0));strip.show();
strip.setPixelColor(S,strip.Color(0,0,0));strip.show();
}

//Theatre-style crawling lights.
void theaterChase(uint32_t c, uint8_t wait) {
for (int j=0; j<10; j++) { //do 10 cycles of chasing
for (int q=0; q < 3; q++) {
for (int i=0; i < strip.numPixels(); i=i+3) {
strip.setPixelColor(i+q, c); //turn every third pixel on
}
strip.show();

delay(wait);

for (int i=0; i < strip.numPixels(); i=i+3) {
strip.setPixelColor(i+q, 0); //turn every third pixel off
}
}
}
}