FallDetector

// these constants describe the pins. They won't change:
const int xpin = A0;                  // x-axis of the accelerometer
const int ypin = A1;                  // y-axis
const int zpin = A2;                  // z-axis (only on 3-axis models)
int ledPin = 6;
const int piezo = 9;
int xa = 0;
int ya = 0;
int za = 0;

int sampleDelay = 100;   //number of milliseconds between readings

void setup()
{
  // initialize the serial communications:
  Serial.begin(9600);
  Serial.println("Starting up");
  tone(piezo, 2000, 500);
  //Make sure the analog-to-digital converter takes its reference voltage from
  // the AREF pin
  analogReference(EXTERNAL);

  pinMode(xpin, INPUT);
  pinMode(ypin, INPUT);
  pinMode(zpin, INPUT);
}

void loop()
{
  int x = analogRead(xpin);

  //add a small delay between pin readings.  I read that you should
  //do this but haven't tested the importance
    delay(1); 

  int y = analogRead(ypin);

  //add a small delay between pin readings.  I read that you should
  //do this but haven't tested the importance
    delay(1); 

  int z = analogRead(zpin);

  //zero_G is the reading we expect from the sensor when it detects
  //no acceleration.  Subtract this value from the sensor reading to
  //get a shifted sensor reading.
  float zero_G = 512.0; 

  //scale is the number of units we expect the sensor reading to
  //change when the acceleration along an axis changes by 1G.
  //Divide the shifted sensor reading by scale to get acceleration in Gs.
  float scale = 102.3;
  
  xa = ((float)x - zero_G)/scale; // calculates x acceleration
  ya =((float)y - zero_G)/scale; // calculates y acceleration 
  za = ((float)z - zero_G)/scale; // calculates z acceleration
  
  Serial.print(((float)x - zero_G)/scale);
  Serial.print("\t");  Serial.print(((float)y - zero_G)/scale);
  Serial.print("\t");  Serial.print(((float)z - zero_G)/scale);
  Serial.print("\n");  // delay before next reading:
  delay(sampleDelay);
if (sqrt(sq(xa) + sq(ya) + sq(za)) > 2.5) { 
digitalWrite(ledPin, HIGH);
tone(piezo, 4000, 1500);
Serial.print("Fall");
delay(3000); //this code keeps LED on for 3 seconds just for interaction purposes
}
else digitalWrite(ledPin, LOW);
}