/*
*This code is for an instructable on "Backpack Security" at:
* ""
*by: Adam Berger
*You are free to use this code anyway you'd like. Thank you for your interest
*in my project!
*/

//pin definitions
#define trigPin 2
#define echoPin 4
#define buzzerPin 0
//constant definitions
#define DELAY_BEFORE_INITIAL 5000
#define ALARM_DISTANCE 35
#define BUZZER_FREQ 500
//variables
boolean alarm = false;
long currentDistance;

void setup() {
  //setup pins
  pinMode(buzzerPin, OUTPUT);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  //delay before beginning loop
  delay(DELAY_BEFORE_INITIAL);
}

void loop() {
  if(!alarm){
  //check distance
  long duration, distance;
  digitalWrite(trigPin, LOW);  // Added this line
  delayMicroseconds(2); // Added this line
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10); // Added this line
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = (duration/2) / 29.1;  
  //if distance is greater than ALARM_DISTANCE begin alarm
  if(distance>=ALARM_DISTANCE)
    alarm=true;
  }
  else{
    delay(BUZZER_FREQ);
    digitalWrite(buzzerPin, HIGH);
    delay(BUZZER_FREQ);
    digitalWrite(buzzerPin,LOW);
  }
}