+/*
+An Arduino code example for interfacing with the HMC5883
+
+by: Jordan McConnell
+ SparkFun Electronics
+ created on: 6/30/11
+ license: OSHW 1.0, http://freedomdefined.org/OSHW
+
+Analog input 4 I2C SDA
+Analog input 5 I2C SCL
+
+Link: https://www.sparkfun.com/tutorials/301
+Datasheet e registri: http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Sensors/Magneto/HMC5883L-FDS.pdf
+*/
+
+#include <Wire.h> //I2C Arduino Library
+
+#define address 0x1E //0011110b, I2C 7bit address of HMC5883
+
+void setup(){
+ //Initialize Serial and I2C communications
+ Serial.begin(9600);
+ Wire.begin();
+
+ //Put the HMC5883 IC into the correct operating mode
+ Wire.beginTransmission(address); //open communication with HMC5883
+ Wire.write(0x00); //select mode Measurement Configuration Bits
+ Wire.write(0x70); // 8 -average, 15 Hz default, normal measuremen
+ Wire.write(0x02); //select mode register
+ Wire.write(0x00); //continuous measurement mode
+ Wire.endTransmission();
+}
+
+void loop(){
+
+ int x,y,z; //triple axis data
+
+ //Tell the HMC5883 where to begin reading data
+ Wire.beginTransmission(address);
+ Wire.write(0x03); //select register 3, X MSB register
+ Wire.endTransmission();
+
+
+ //Read data from each axis, 2 registers per axis
+ Wire.requestFrom(address, 6);
+ if(6<=Wire.available()){
+ x = Wire.read()<<8; //X msb
+ x |= Wire.read(); //X lsb
+ z = Wire.read()<<8; //Z msb
+ z |= Wire.read(); //Z lsb
+ y = Wire.read()<<8; //Y msb
+ y |= Wire.read(); //Y lsb
+ }
+
+ //Print out values of each axis
+ Serial.print("x: ");
+ Serial.print(x);
+ Serial.print(" y: ");
+ Serial.print(y);
+ Serial.print(" z: ");
+ Serial.print(z);
+ // Calcolo cotangente per gradi: https://it.wikipedia.org/wiki/Arcotangente2
+ float radianti = atan2(x,y) ;
+ if (radianti < 0) {// Se y e'antiorario il segno e' inverso
+ radianti += 2 * PI ; // inverte il segno
+}
+
+ float gradi = radianti * 180 / PI; // Conversione in gradi
+ gradi += 2.56 ; // Correzione per la declinazione magnetica locale
+ // Modena dovrebbe essere a +2° 34' positivi EST
+ Serial.print(" gradi: ");
+ Serial.println(gradi);
+
+ delay(250);
+}