Arduino is an open-source microprocessor platform to build electronics prototypes. Not only the development tools are open-source, but also the hardware itself. You can download all the necessary plans for it and build your own one, if you want to.

The really cool thing about the Arduino is, that you can program it with the open-source programming language Wiring, which is very straightforward to use.

Of course, being a complete newbie in electronics engineering, I ordered my own Arduino board as a prebuilt base-board – the Arduino Duemilanove…
…and finally, it arrived :)

As a first act of familiarization, I started with the very basic “push a button to power the LED” program

int ledPin = 13; // choose the pin for the LED
int inPin = 2;    // choose the input pin (for a pushbutton)
int val = 0;      // variable for reading the pin status

void setup() {
  pinMode(ledPin, OUTPUT);  // declare LED as output
  pinMode(inPin, INPUT);      // declare pushbutton as input
}

void loop(){
  val = digitalRead(inPin);   // read input value
  if (val == HIGH) {           // check if the input is HIGH (button released)
    digitalWrite(ledPin, LOW);  // turn LED OFF
  } else {
    digitalWrite(ledPin, HIGH);  // turn LED ON
  }
}