Examples > Communication

Virtual Switch

An example of using the Arduino board to receive data from the computer. In this case, the Arduino boards turns on an LED when it receives the character 'H', and turns off the LED when it receives the character 'L'.

The data can be sent from the Arduino serial monitor, or another program like Processing (see code below), Flash (via a serial-net proxy), PD, or Max/MSP.


An LED on pin 13.


int outputPin = 13;
int val;

void setup()
  pinMode(outputPin, OUTPUT);

void loop()
  if (Serial.available()) {
    val = Serial.read();
    if (val == 'H') {
      digitalWrite(outputPin, HIGH);
    if (val == 'L') {
      digitalWrite(outputPin, LOW);

Processing Code

// mouseover serial 
// by BARRAGAN <http://people.interaction-ivrea.it/h.barragan> 

// Demonstrates how to send data to the Arduino I/O board, in order to 
// turn ON a light if the mouse is over a rectangle and turn it off 
// if the mouse is not. 

// created 13 May 2004 

import processing.serial.*; 

Serial port; 

void setup() 
  size(200, 200); 

  // List all the available serial ports in the output pane. 
  // You will need to choose the port that the Arduino board is 
  // connected to from this list. The first port in the list is 
  // port #0 and the third port in the list is port #2. 

  // Open the port that the Arduino board is connected to (in this case #0) 
  // Make sure to open the port at the same speed Arduino is using (9600bps) 
  port = new Serial(this, Serial.list()[0], 9600); 

// function to test if mouse is over square 
boolean mouseOverRect() 
  return ((mouseX >= 50)&&(mouseX <= 150)&&(mouseY >= 50)&(mouseY <= 150)); 

void draw() 
  if(mouseOverRect())      // if mouse is over square 
    fill(#BBBBB0);         // change color 
    port.write('H');       // send an 'H' to indicate mouse is over square 
  } else { 
    fill(#666660);         // change color 
    port.write('L');       // send an 'L' otherwise 
  rect(50, 50, 100, 100);  // draw square