////////////////////////////////////////////////////////////////////////////////
// Name:       GY-521                                                         //
//             Compass GY-273 with Honeywell HMC5883L chip                    //
// Platform:   Arduino Uno R3                                                 //
// Created by: HARB, June 2016, GPL copyrights                                //
// http://robotigs.com/robotigs/includes/parts_header.php?idpart-8            //
// Connect the GY-273 to the default SDA and SCL on your Arduino UNO board.   //
// Read out the result on the serial monitor. No extra resistors are needed.  //
////////////////////////////////////////////////////////////////////////////////

// SET PRECOMPILER OPTIONS *****************************************************
// Define precompiler variables ------------------------------------------------
bool    ledBinVal = LOW;                      //You can chose HIGH-on or LOW-off

//Declare variables ------------------------------------------------------------
const int HMC5883addr = 0x1E;       //I2C address of the HMC5883L, 3C becomes 1E
int16_t Xaxis, Yaxis, Zaxis, Tmp, GyX, GyY, GyZ;   //Values to read from compass

///Define the needed header files for the precompiler, no charge if not used ---
#include <Wire.h>      //This is a very bad I²C library, but the most compatible
//END OF PRECOMPILER OPTIONS ---------------------------------------------------


void setup() { //Setup runs once ***********************************************
  Serial.begin(9600);   //Nothing more needed for the Serial Monitor to function
  pinMode(LED_BUILTIN, OUTPUT);          //Arduino boards contain an onboard LED
  
  Wire.begin();                          //Just needed once to start I²C library
  Wire.beginTransmission(HMC5883addr);             //Claim the I²C bus as master
  Wire.write(0x02);                                              //Mode register
  Wire.write(0);                               //Set Continuous Measurement Mode
  Wire.endTransmission(true);                //Stop session and free the I²C bus
}//--(end setup )---------------------------------------------------------------


void loop() { //KEEP ON RUNNING THIS LOOP FOREVER ******************************
  Wire.beginTransmission(HMC5883addr);             //Claim the I²C bus as master
  Wire.write(0x03);   //Start writing register 0x03 = Data Output X MSB Register
  Wire.endTransmission(false);              //Stop session but keep bus occupied

  while (digitalRead(19) == 1){}           //Wait here for DRDY to be pulled low

  Wire.requestFrom(HMC5883addr, 6, true); //Request a block total of 6 registers
  Xaxis = Wire.read() << 8 | Wire.read();    //0x03 = Data Output X MSB Register
  Zaxis = Wire.read() << 8 | Wire.read();    //0x05 = Data Output Z MSB Register
  Yaxis = Wire.read() << 8 | Wire.read();    //0x07 = Data Output Y MSB Register

  Serial.print("X"); Serial.print(Xaxis);
  Serial.print(" | Y"); Serial.print(Yaxis);
  Serial.print(" | Z"); Serial.println(Zaxis);
  toggle_ledBin();                  //Toggles the default on-board LED on or off
  delay(1000);                             //You can test your own patience here
} //End of void loop()                       //KEEP ON RUNNING THIS LOOP FOREVER
//345678911234567892123456789312345678941234567895123456789612345678971234567898

void toggle_ledBin(void) { //Toggles the default on-board LED on or off ********
  ledBinVal = !ledBinVal;                                         //Toggle value
  digitalWrite(LED_BUILTIN, ledBinVal);         //Set Arduino boards onboard LED
} //Exit toggle_ledBin ---------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
// PIN ALLOCATIONS TABLE ARDUINO UNO                                          //
// Board -Atmel- PIN - IDE - Function          - Connection               ALT //
//                                                                            //
// CONNECTIONS RAILS TOP LEFT: DIGITAL PWM<~> ******************************* //
// SCL   -  28 - PC5 -19/A5- ADC5/SCL/PCINT13  - White cable to GY-521    TWI //
// SDA   -  27 - PC4 -18/A4- ADC4/SDA/PCINT12  - Yellow cable to GY-521   TWI //
// AREF  -  21 - REF -     - AREF              -                              //
// GND   -  22 - GND -     - GND               -                              //
// 13    -  19 - PB5 -  13 - SCK/PCINT5        - LED_BUILTIN Arduino      SPI //
// 12    -  18 - PB4 -  12 - MISO/PCINT4       -                          SPI //
// ~11   -  17 - PB3 -  11 - MOSI/OC2A/PCINT3  -                          PWM //
// ~10   -  16 - PB2 -  10 - SS/OC1B/PCINT2    -                          PWM //
// ~9    -  15 - PB1 -   9 - OC1A/PCINT1       -                          PWM //
// 8     -  14 - PB0 -   8 - PCINT0/CLK0/ICP1  -                          DIO //
//                                                                            //
// CONNECTIONS RAILS TOP RIGHT: DIGITAL PWM<~> ****************************** //
// 7     -  13 - PD7 -   7 - PCINT23/AIN1      -                          DIO //
// ~6    -  12 - PD6 -   6 - PCINT22/OCA0/AIN0 -                          PWM //
// ~5    -  11 - PD5 -   5 - PCINT21/OC0B/T1   -                          PWM //
// ~4    -   6 - PD4 -   4 - PCINT20/XCK/T0    -                          PWM //
// ~3    -   5 - PD3 -   3 - PCINT19/OC2B/INT1 -                          INT //
// ~2    -   4 - PD2 -   2 - PCINT18/INT0      -                          INT //
// TX->1 -   3 - PD1 -   1 - PCINT17/TXD       - Serial monitor           TXD //
// RX<-0 -   2 - PD0 -   0 - PCINT16/RCD       - Serial Monitor           RCD //
//                                                                            //
// CONNECTIONS RAILS BOTTOM LEFT: POWER ************************************* //
// 5V    -   7 - VCC -      - VCC              - Output to breadboard     VCC //
// RES   -   1 - RES -      - PCINT14/RESET    -                          RES //
// 3.3V  -     -     -     -                   -                              //
// 5V    -     -     -     -                   -                              //
// GND   -     -     -     -                   -                              //
// GND   -     -     -     -                   -                              //
// Vin   -     -     -     -                   -                              //
//                                                                            //
// CONNECTIONS RAILS BOTTOM RIGHT: ANALOG IN ******************************** //
// A0    -  23 - PC0 -A0/14- ADC0/PCINT8       -                          ADC //
// A1    -  24 - PC1 -A1/15- ADC1/PCINT9       -                          ADC //
// A2    -  25 - PC2 -A2/16- ADC2/PCINT10      -                          ADC //
// A3    -  26 - PC3 -A3/17- ADC3/PCINT12      -                          ADC //
// A4    -  27 - PC4 -A4/18- ADC4/SDA/PCINT12  -                          TWI //
// A5    -  28 - PC5 -A5/19- ADC5/SCL/PCINT13  -                          TWI //
////////////////////////////////////////////////////////////////////////////////
// EEPROM MEMORY MAP:                                                         //
// Start End  Number Description                                              //
// 0000  0000      1 Never use this memory location to be AVR compatible      //
////////////////////////////////////////////////////////////////////////////////
//345678911234567892123456789312345678941234567895123456789612345678971234567898