Overview of Accelerometer 

Accelerometer is an electromechanical device that measures the force of acceleration due to gravity in g unit.

It can be used in applications requiring tilt sensing.

The ADXL335 measures acceleration along X, Y and Z axes and gives analog voltage output proportional to the acceleration along these 3 axes.

Microcontrollers can process these voltages by converting them to digital signals using ADC.

For more information about ADXL335 accelerometer and how to use it, refer the topic ADXL335 Accelerometer Module in the sensors and modules section.

Connection Diagram of Accelerometer ADXL335 with Arduino

Read Accelerometer ADXL335 Using Arduino Uno

Finding the roll and pitch of the device using analog voltages of accelerometer module and displaying them on serial monitor of Arduino .

Accelerometer ADXL335 Code With Arduino Uno

#include <math.h>
const int x_out = A1; /* connect x_out of module to A1 of UNO board */
const int y_out = A2; /* connect y_out of module to A2 of UNO board */
const int z_out = A3; /* connect z_out of module to A3 of UNO board */

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

void loop() {
  int x_adc_value, y_adc_value, z_adc_value; 
  double x_g_value, y_g_value, z_g_value;
  double roll, pitch, yaw;
  x_adc_value = analogRead(x_out); /* Digital value of voltage on x_out pin */ 
  y_adc_value = analogRead(y_out); /* Digital value of voltage on y_out pin */ 
  z_adc_value = analogRead(z_out); /* Digital value of voltage on z_out pin */ 
  Serial.print("x = ");
  Serial.print(x_adc_value);
  Serial.print("\t\t");
  Serial.print("y = ");
  Serial.print(y_adc_value);
  Serial.print("\t\t");
  Serial.print("z = ");
  Serial.print(z_adc_value);
  Serial.print("\t\t");
  //delay(100);
  
  x_g_value = ( ( ( (double)(x_adc_value * 5)/1024) - 1.65 ) / 0.330 ); /* Acceleration in x-direction in g units */ 
  y_g_value = ( ( ( (double)(y_adc_value * 5)/1024) - 1.65 ) / 0.330 ); /* Acceleration in y-direction in g units */ 
  z_g_value = ( ( ( (double)(z_adc_value * 5)/1024) - 1.80 ) / 0.330 ); /* Acceleration in z-direction in g units */ 

  roll = ( ( (atan2(y_g_value,z_g_value) * 180) / 3.14 ) + 180 ); /* Formula for roll */
  pitch = ( ( (atan2(z_g_value,x_g_value) * 180) / 3.14 ) + 180 ); /* Formula for pitch */
  //yaw = ( ( (atan2(x_g_value,y_g_value) * 180) / 3.14 ) + 180 ); /* Formula for yaw */
  /* Not possible to measure yaw using accelerometer. Gyroscope must be used if yaw is also required */

  Serial.print("Roll = ");
  Serial.print(roll);
  Serial.print("\t");
  Serial.print("Pitch = ");
  Serial.print(pitch);
  Serial.print("\n\n");
  delay(1000);
}

Video of Accelerometer Using Arduino Uno