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arduino_serial.pde

// Pin 13 has an LED connected on most Arduino boards.
// give it a name:
int incomingByte = 0;
int led = 13;

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.
  pinMode(led, OUTPUT);
  Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {
  if (Serial.available() > 0) {
    incomingByte = Serial.read();
    if(incomingByte == 'x'){
      digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
      delay(1000);               // wait for a second
    }
  }
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
}