import processing.serial.*;
  
  Serial myPort;  // Create object from Serial class
  int val;      // Data received from the serial port
  
  void setup() 
  {
    size(200, 200);
    // I know that the first port in the serial list on my mac
    // is always my  FTDI adaptor, so I open Serial.list()[0].
    // On Windows machines, this generally opens COM1.
    // Open whatever port is the one you're using.
    String portName = Serial.list()[0];
    myPort = new Serial(this, portName, 9600);
  }
  
  void draw()
  {
    if ( myPort.available() > 0) {  // If data is available,
      val = myPort.read();         // read it and store it in val
    }
    background(255);             // Set background to white
    if (val == 0) {              // If the serial value is 0,
      fill(0);                   // set fill to black
    } 
    else {                       // If the serial value is not 0,
      fill(204);                 // set fill to light gray
    }
    rect(50, 50, 100, 100);
  }
  
  /*
  
  // Wiring / Arduino Code
  // Code for sensing a switch status and writing the value to the serial port.
  
  int switchPin = 4;                       // Switch connected to pin 4
  
  void setup() {
    pinMode(switchPin, INPUT);             // Set pin 0 as an input
    Serial.begin(9600);                    // Start serial communication at 9600 bps
  }
  
  void loop() {
    if (digitalRead(switchPin) == HIGH) {  // If switch is ON,
      Serial.print(1, BYTE);               // send 1 to Processing
    } else {                               // If the switch is not ON,
      Serial.print(0, BYTE);               // send 0 to Processing
    }
    delay(100);                            // Wait 100 milliseconds
  }
  
  */