Sensor control LED

http://webzone.k3.mah.se/projects/arduino-workshop/projects/arduino_meets_processing/instructions/ldr.html

/*
* ap_ReadAnalog
*
* Reads an analog input from the input pin and sends the value
* followed by a line break over the serial port.
*
* This file is part of the Arduino meets Processing Project:
* For more information visit http://www.arduino.cc.
*
* copyleft 2005 by Melvin Ochsmann for Malm´┐Ż University
*
*/

// variables for input pin and control LED
int analogInput = 3;
int LEDpin = 13;

// variable to store the value
int value = 0;

// a threshold to decide when the LED turns on
int threshold = 512;

void setup(){

// declaration of pin modes
pinMode(analogInput, INPUT);
pinMode(LEDpin, OUTPUT);

// begin sending over serial port
beginSerial(9600);
}

void loop(){
// read the value on analog input
value = analogRead(analogInput);

// if value greater than threshold turn on LED
if (value < threshold) digitalWrite(LEDpin, HIGH); else digitalWrite(LEDpin, LOW);

// print out value over the serial port
printInteger(value);

// and a signal that serves as seperator between two values
printByte(10);

// wait for a bit to not overload the port
delay(10);
}