This example shows how to send data from a personal computer to an Arduino board to control the brightness of an LED. The data is sent in individual bytes, each of which ranges in value from 0 to 255. Arduino reads these bytes and uses them to set the brightness of the LED.

You can send bytes to the Arduino from any software that can access the computer serial port. Examples for Processing and Max/MSP version 5 are shown below.

Arduino Board LED 220 ohm resistor Software Required

Processing or Max/MSP version 5 Circuit

An LED connected to pin 9. Use an appropriate resistor as needed. For most common LEDs, a 220 or 330 ohm resistor will work.

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image developed using Fritzing. For more circuit examples, see the Fritzing project page

Schematic

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/*
  Dimmer
 
 Demonstrates the sending data from the computer to the Arduino board,
 in this case to control the brightness of an LED.  The data is sent
 in individual bytes, each of which ranges from 0 to 255.  Arduino
 reads these bytes and uses them to set the brightness of the LED.
 
 The circuit:
 LED attached from digital pin 9 to ground.
 Serial connection to Processing, Max/MSP, or another serial application
 
 created 2006
 by David A. Mellis
 modified 30 Aug 2011
 by Tom Igoe and Scott Fitzgerald
 
 This example code is in the public domain.
 
 http://www.arduino.cc/en/Tutorial/Dimmer
 
 */
 
const int ledPin = 9;      // the pin that the LED is attached to
 
void setup()
{
  // initialize the serial communication:
  Serial.begin(9600);
  // initialize the ledPin as an output:
  pinMode(ledPin, OUTPUT);
}
 
void loop() {
  byte brightness;
 
  // check if data has been sent from the computer:
  if (Serial.available()) {
    // read the most recent byte (which will be from 0 to 255):
    brightness = Serial.read();
    // set the brightness of the LED:
    analogWrite(ledPin, brightness);
  }
}

Processing code for this example

 // Dimmer - sends bytes over a serial port
 // by David A. Mellis
 //This example code is in the public domain.
 
 import processing.serial.*;
 Serial port;
 
 void setup() {
 size(256, 150);
 
 println("Available serial ports:");
 println(Serial.list());
 
 // Uses the first port in this list (number 0).  Change this to
 // select the port corresponding to your Arduino board.  The last
 // parameter (e.g. 9600) is the speed of the communication.  It
 // has to correspond to the value passed to Serial.begin() in your
 // Arduino sketch.
 port = new Serial(this, Serial.list()[0], 9600);  
 
 // If you know the name of the port used by the Arduino board, you
 // can specify it directly like this.
 //port = new Serial(this, "COM1", 9600);
 }
 
 void draw() {
 // draw a gradient from black to white
 for (int i = 0; i < 256; i++) {
 stroke(i);
 line(i, 0, i, 150);
 }
 
 // write the current X-position of the mouse to the serial port as
 // a single byte
 port.write(mouseX);
 }
 
 

Processing Code

The Processing sketch in the code sample above will send bytes out the serial port to the Arduino to dim the LED.