Home > Arduino Projects > Intro to 3-Axis Accelerometer
Description:

3-Axis accelerometers provide a way to interface with the physical world.  It's used in robotics for tilt and motion sensing, game controllers for input, mobile phones for image stabilization, etc.  Lots of interesting uses!  The well-commented code in this project will help you get started, even if you've never used a 3-axis accelerometer before.
  
In this project, an accelerometer functions as a nifty little motion detector.  Want to know who is stealing from the cookie jar?  Want a simple home intrusion detector?  Or to test your partner's driving skills? Then have a look at this:

Video:


Parts Required:


Build Instructions:

  1. Overlay the Seeed Studio Base Shield onto the Freetronics Eleven (or compatible Arduino).
  2. Use a Universal Cable to attach a Seeed Studio Grove Button to Analog Pin 0 on the Base Shield. The socket is located directly above the Freetronics Eleven Power plug, and next to the Reset button on the Base Shield. Please note that Analog Pin 1 is not used by the Grove Button.
  3. Use a universal Cable to attache a Seeed Studio Grove Buzzer to Analog Pin 1 on the Base Shield. This is the socket next to the one used in Step 2.
  4. Solder the female header pins to the Protoboard. Overlay the protoboard onto the Base Shield to create a third layer. I created this layer to tidy up the project and make it a little bit more portable. You could just wire up another breadboard on the side.
  5. Stick a mini-breadboard (4.5cm x 3.5cm) onto the protoboard. This allows you to use the protoboard for other projects.
  6. Solder the male headers to the 3-axis accelerometer, and then place it centrally onto the breadboard.
  7. You need 5 wires to connect:
    • GND on protoboard to GND on accelerometer
    • 5V on protoboard to     VIN on accelerometer
    • Analog Pin 3 on protoboard to X on accelerometer
    • Analog Pin 4 on protoboard to Y on accelerometer
    • Analog Pin 5 on protoboard to Z on accelerometer
  8. Connect digital pin 8 to an LED and 330 ohm resistor on the breadboard,
  9. Use a wire to connect the resistor mentioned above to GND on the protoboard
  10. Connect the USB cable from your computer to the Freetronics Eleven, and upload the Arduino Sketch to the board. 
  11. Disconnect the USB cable, and then power the Freetronics Eleven using a 9V battery and clip.
  12. When you press the button, it will sound 3 warning sounds before it becomes activated.
  13. If it detects a vibration or motion that exceeds the tolerance level, it will alarm. The alarm will continue until you either press the Grove button - which resets and reactivates the device or you can press the Reset button on the Base Shield to Stop monitoring for motion.
Sketch:


Sketch

Sketch

Sketch

Freetronics' Eleven / Arduino Sketch:


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//Motion Detector Alarm - Written by ScottC on 2/08/2012

//Global Variables and constants
const int buttonPin = A0; // button Pin connected to Analog 0
const int buzzerPin = A1; // buzzer Pin connected to Analog 1


//Accelerometer Pins
const int x = A3; // X pin connected to Analog 3
const int y = A4; // Y pin connected to Analog 4
const int z = A5; // Z pin connected to Analog 5


//Alarm LED
const int ledPin = 8; // LED connected to Digital 8



int tolerance=20; // Sensitivity of the Alarm
boolean calibrated=false; // When accelerometer is calibrated - changes to true
boolean moveDetected=false; // When motion is detected - changes to true



//Accelerometer limits
int xMin; //Minimum x Value
int xMax; //Maximum x Value
int xVal; //Current x Value

int yMin; //Minimum y Value
int yMax; //Maximum y Value
int yVal; //Current y Value

int zMin; //Minimum z Value
int zMax; //Maximum z Value
int zVal; //Current z Value



void setup(){
//Begin Serial communication
Serial.begin(38400);

//Initilise LED Pin
pinMode(ledPin, OUTPUT);

}



void loop(){
// If the button is pressed, initialise and recalibrate the Accelerometer limits.
if(analogRead(buttonPin)>500){
calibrateAccel();
}

// Once the accelerometer is calibrated - check for movement
if(calibrated){
if(checkMotion()){
moveDetected=true;
}
}

// If motion is detected - sound the alarm !
if(moveDetected){
Serial.println("ALARM");
ALARM();
delay(1000);
}

}





//This is the function used to sound the buzzer
void buzz(int reps, int rate){
for(int i=0; i<reps; i++){
analogWrite(buzzerPin,900);
delay(100);
analogWrite(buzzerPin,0);
delay(rate);
}
}




// Function used to calibrate the Accelerometer
void calibrateAccel(){
// reset alarm
moveDetected=false;

//initialise x,y,z variables
xVal = analogRead(x);
xMin = xVal;
xMax = xVal;

yVal = analogRead(y);
yMin = yVal;
yMax = yVal;

zVal = analogRead(z);
zMin = zVal;
zMax = zVal;

// Calibration sequence initialisation sound - 3 seconds before calibration begins
buzz(3,1000);

//calibrate the Accelerometer (should take about 0.5 seconds)
for (int i=0; i<50; i++){
// Calibrate X Values
xVal = analogRead(x);
if(xVal>xMax){
xMax=xVal;
}else if (xVal < xMin){
xMin=xVal;
}

// Calibrate Y Values
yVal = analogRead(y);
if(yVal>yMax){
yMax=yVal;
}else if (yVal < yMin){
yMin=yVal;
}

// Calibrate Z Values
zVal = analogRead(z);
if(zVal>zMax){
zMax=zVal;
}else if (zVal < zMin){
zMin=zVal;
}

//Delay 10msec between readings
delay(10);
}

//End of calibration sequence sound. ARMED.
buzz(3,40);
printValues(); //Only useful when connected to computer- using serial monitor.
calibrated=true;

}



//Function used to detect motion. Tolerance variable adjusts the sensitivity of movement detected.
boolean checkMotion(){
boolean tempB=false;
xVal = analogRead(x);
yVal = analogRead(y);
zVal = analogRead(z);

if(xVal >(xMax+tolerance)||xVal < (xMin-tolerance)){
tempB=true;
Serial.print("X Failed = ");
Serial.println(xVal);
}

if(yVal >(yMax+tolerance)||yVal < (yMin-tolerance)){
tempB=true;
Serial.print("Y Failed = ");
Serial.println(yVal);
}

if(zVal >(zMax+tolerance)||zVal < (zMin-tolerance)){
tempB=true;
Serial.print("Z Failed = ");
Serial.println(zVal);
}

return tempB;
}





// Prints the Sensor limits identified during Accelerometer calibration.
// Prints to the Serial monitor.
void printValues(){
Serial.print("xMin=");
Serial.print(xMin);
Serial.print(", xMax=");
Serial.print(xMax);
Serial.println();

Serial.print("yMin=");
Serial.print(yMin);
Serial.print(", yMax=");
Serial.print(yMax);
Serial.println();

Serial.print("zMin=");
Serial.print(zMin);
Serial.print(", zMax=");
Serial.print(zMax);
Serial.println();

Serial.println("------------------------");
}




//Function used to make the alarm sound, and blink the LED.
void ALARM(){

//don't check for movement until recalibrated again
calibrated=false;

// sound the alarm and blink LED
digitalWrite(ledPin, HIGH);
buzz(4,20);
digitalWrite(ledPin, LOW);
}

For more awesome projects, or more info on this project, check out ScottC's Arduino Basics Blog