Intruders better beware!

IntruderAlert.ino

/*
IntruderAlert

Intruders better beware!

Every time the value from the ultrasonic range finder drops below the
potentiometer's threshold value, an alarm is triggered. In this case the alarm
is an LED, but it could easily be a buzzer. If your Arduino is connected to a
PC then you can also use the serial monitor to read the debug information of
the two analogue devices.

This work is licensed under the Creative Commons Attribution-ShareAlike 2.5 UK:
Scotland License. To view a copy of this license, visit
http://creativecommons.org/licenses/by-sa/2.5/scotland/ or send a letter to
Creative Commons, 444 Castro Street, Suite 900, Mountain View, California,
94041, USA.

Copyright 2013, Mike Coats
http://mikecoats.com/IntruderAlert/
i.am@mikecoats.com
*/

int LedPin = 8;

void setup() {
  // Initialise the serial port for debugging.
  Serial.begin(9600);

  // Set up the "alarm" pin.
  pinMode(LedPin,OUTPUT);
}

void loop() {
  // Grab the value from the ultrasonic range finder.
  int sonarValue = analogRead(A0);

  // Grab the value from the calibraiton potentiometer.
  int resValue = analogRead(A1);

  // Output the debugging message.
  Serial.print(sonarValue);
  Serial.print(" - ");
  Serial.println(resValue);
  
  // If the sensor's value indicates that an object is "closer" than the
  //calibration threshold.
  if(sonarValue < resValue)
  {
    // Turn the "alarm" to on.
    digitalWrite(LedPin,HIGH);
  }
  else
  {
    // Turn off the "alarm".
    digitalWrite(LedPin,LOW);
  }
  
  // Hang on for a bit, running the whole loop 8 times a second.
  delay(125);
}