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Examples > Analog I/O

ADXL3xx Accelerometer

Reads an Analog Devices ADXL3xx series (e.g. ADXL320, ADXL321, ADXL322, ADXL330) accelerometer and communicates the acceleration to the computer. The pins used are designed to be easily compatible with the breakout boards from Sparkfun. The ADXL3xx outputs the acceleration on each axis as an analog voltage between 0 and 5 volts, which is read by an analog input on the Arduino.

Circuit

An ADXL322 on a Sparkfun breakout board inserted into the analog input pins of an Arduino.

Pinout for the above configuration:

Breakout Board Pin	Self-Test	Z-Axis	Y-Axis	X-Axis	Ground	VDD
Arduino Analog Input Pin	0	1	2	3	4	5

Or, if you're using just the accelerometer:

ADXL3xx Pin	Self-Test	ZOut	YOut	XOut	Ground	VDD
Arduino Pin	None (unconnected)	Analog Input 1	Analog Input 2	Analog Input 3	GND	5V

Code

int groundpin = 18;             // analog input pin 4
int powerpin = 19;              // analog input pin 5
int xpin = 3;                   // x-axis of the accelerometer
int ypin = 2;                   // y-axis
int zpin = 1;                   // z-axis (only on 3-axis models)

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

  // Provide ground and power by using the analog inputs as normal
  // digital pins.  This makes it possible to directly connect the
  // breakout board to the Arduino.  If you use the normal 5V and
  // GND pins on the Arduino, you can remove these lines.
  pinMode(groundPin, OUTPUT);
  pinMode(powerPin, OUTPUT);
  digitalWrite(groundPin, LOW); 
  digitalWrite(powerPin, HIGH);
}

void loop()
{
  Serial.print(analogRead(xpin));
  Serial.print(" ");
  Serial.print(analogRead(ypin));
  Serial.print(" ");
  Serial.print(analogRead(zpin));
  Serial.println();
  delay(1000);
}

Data

Here are some accelerometer readings collected by the positioning the y-axis of an ADXL322 2g accelerometer at various angles from ground. Values should be the same for the other axes, but will vary based on the sensitivity of the device. With the axis horizontal (i.e. parallel to ground or 0°), the accelerometer reading should be around 512, but values at other angles will be different for a different accelerometer (e.g. the ADXL302 5g one).

Angle	-90	-80	-70	-60	-50	-40	-30	-20	-10	0	10	20	30	40	50	60	70	80	90
Acceleration	662	660	654	642	628	610	589	563	537	510	485	455	433	408	390	374	363	357	355