ADXL345 Accelerometer Sensor – How to Use it?

Introduction:

ADXL345 is also a triple axis accelerometer but with a bit of different specifications. It has free fall detection as well as double/single tap detection in it. It uses I2C protocol for communication.

Accelerometer works on the principle of Piezoelectric effect. whenever we will tilt the sensor the ball is supposed to move in that direction because of Gravitational force. The walls are made of Piezoelectric elements. So, every time ball is touching the wall an electric current will be produced which will be interpreted in the form of values in any 3D space.

I2C Protocol:

I2C protocol only requires two wires to start off a communication but those two wires can support upto 1008 slave devices. I2C communication is preffered only for short distance communication. I2C allows multi-master multi-slave system i.e. several number of master devices can communicate with several number or slave devices.

Where to use?

We can use ADXL345 in Smart Phones, Medical Instrumentation, Gaming and Pointing devices, Personal Navigation devices etc.

Application:

http://www.arduinoprojects.net/sensor-projects/arduino-adxl345-accelerometer-example.php

Required Library – https://github.com/adafruit/Adafruit_ADXL345

Project for Reference:

Code:

#include <Wire.h> // I2C library, gyroscope

// Accelerometer ADXL345

#define ACC (0xA7>>1)    //ADXL345 ACC address

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

void initAcc() {

//Turning on the ADXL345

writeTo(ACC, 0x2D, 1<<3);      

writeTo(ACC, 0x31, 0x0B);

writeTo(ACC, 0x2C, 0x09);

//by default the device is in +-2g range reading

}

void getAccelerometerData(int * result) {

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

byte buff[A_TO_READ];

readFrom(ACC, regAddress, A_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

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

result[1] = (((int)buff[3])<< 8) | buff[2];

result[2] = (((int)buff[5]) << 8) | buff[4];

}

void setup()

{

Serial.begin(9600);

Wire.begin();

initAcc();

}

void loop()

{

int hx,hy,hz;

int acc[3];

getAccelerometerData(acc);

hx = acc[0];

hy = acc[1];

hz = acc[2];

Serial.print(" X=");

Serial.print(hx);

Serial.print(" Y=");

Serial.print(hy);

Serial.print(" Z=");

Serial.println(hz);

delay(50); 

}

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

//Writes val to address register on ACC

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

 Wire.beginTransmission(DEVICE); //start transmission to ACC 

 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 ACC in to buff array

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

Wire.beginTransmission(DEVICE); //start transmission to ACC 

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

Wire.endTransmission(); //end transmission

Wire.beginTransmission(DEVICE); //start transmission to ACC

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

int i = 0;

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

{ 

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

  i++;

}

Wire.endTransmission(); //end transmission

}