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Examples > Communication

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.

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.

Circuit

An LED connected to pin 9. use appropriate resistor as needed. For most common LEDs, you can usually do without the resistor, as the current output of the digital I/O pins is limited.

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

Schematic

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Code

 /*
   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 14 Apr 2009
  by Tom Igoe and Scott Fitzgerald
  
  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

Run the following sketch in Processing. It will send bytes out the serial port to the Arduino to dim the LED.

 /* Processing code for this example */
  // Dimmer - sends bytes over a serial port
  // by David A. Mellis
  
  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);
  }
  */

Max code

The Max/MSP patch looks like the image below. The text of the patch is linked behind the image. Copy it and paste it into a new patch window.