#include <Wire.h>

#define DEVICE (0x53) //ADXL345 device address

#define TO_READ (6) //num of bytes we are going to read each time (two bytes for each axis)

byte buff[TO_READ] ; //6 bytes buffer for saving data read from the device

char str[512]; //string buffer to transform data before sending it to the serial port

int regAddress = 0x32; //first axis-acceleration-data register on the ADXL345

int x, y, z; //three axis acceleration data

double roll = 0.00, pitch = 0.00; //Roll & Pitch are the angles which rotate by the axis X and y

//in the sequence of R(x-y-z),more info visit

// https://www.dfrobot.com/wiki/index.php?title=How_to_Use_a_Three-Axis_Accelerometer_for_Tilt_Sensing#Introduction

void setup() {

Wire.begin(); // join i2c bus (address optional for master)

Serial.begin(9600); // start serial for output

//Turning on the ADXL345

writeTo(DEVICE, 0x2D, 0);

writeTo(DEVICE, 0x2D, 16);

writeTo(DEVICE, 0x2D, 8);

}

void loop() {

readFrom(DEVICE, regAddress, TO_READ, buff); //read the acceleration data from the ADXL345

//each axis reading comes in 10 bit resolution, ie 2 bytes. Least Significat Byte first!!

//thus we are converting both bytes in to one int

x = (((int)buff[1]) << 8) | buff[0];

y = (((int)buff[3])<< 8) | buff[2];

z = (((int)buff[5]) << 8) | buff[4];

//we send the x y z values as a string to the serial port

Serial.print("The acceleration info of x, y, z are:");

sprintf(str, "%d %d %d", x, y, z);

Serial.print(str);

Serial.write(10);

//Roll & Pitch calculate

RP_calculate();

Serial.print("Roll:"); Serial.println( roll );

Serial.print("Pitch:"); Serial.println( pitch );

Serial.println("");

//It appears that delay is needed in order not to clog the port

delay(500);

}

//---------------- Functions

//Writes val to address register on device

void writeTo(int device, byte address, byte val) {

Wire.beginTransmission(device); //start transmission to device

Wire.write(address); // send register address

Wire.write(val); // send value to write

Wire.endTransmission(); //end transmission

}

//reads num bytes starting from address register on device in to buff array

void readFrom(int device, byte address, int num, byte buff[]) {

Wire.beginTransmission(device); //start transmission to device

Wire.write(address); //sends address to read from

Wire.endTransmission(); //end transmission

Wire.beginTransmission(device); //start transmission to device

Wire.requestFrom(device, num); // request 6 bytes from device

int i = 0;

while(Wire.available()) //device may send less than requested (abnormal)

{

buff[i] = Wire.read(); // receive a byte

i++;

}

Wire.endTransmission(); //end transmission

}

//calculate the Roll&Pitch

void RP_calculate(){

double x_Buff = float(x);

double y_Buff = float(y);

double z_Buff = float(z);

roll = atan2(y_Buff , z_Buff) * 57.3;

pitch = atan2((- x_Buff) , sqrt(y_Buff * y_Buff + z_Buff * z_Buff)) * 57.3;

}