JavaScript-based Arduino Uno communication

[ 05/2011 update ] Demo video | this project is a bit stale, check the future: node-arduino + node-serialport

version: 2010.10.31

Analog Inputs

  • Ain0:
  • Ain1:
  • Ain2:
  • Ain3:
  • Ain4:
  • Ain5:
This is a <canvas> element. You need a better browser to see the data visualization.

Apply variable current to the analog inputs (eg. a potentiometer) to see live graphs.

Standard I/O Pins

  • Pin 2
  • Pin 3
  • Pin 4
  • Pin 5
  • Pin 6
  • Pin 7
  • Pin 8
  • Pin 9
  • Pin 10
  • Pin 11
  • Pin 12
  • Pin 13

Pin 13/LED Blink Test

Pin 13 typically has a surface-mount LED (eg. as with the Uno) representing binary output.

Interval (msec):  


A small shopping list of software is needed to get everything working.

Some serial/socks programs work better on Windows, but I've had good results with SerialNet. I found the Standard Firmata supplied with the Arduino IDE worked with SerialNet (in Processing), both set to run at 115200 baud on a Mac with Snow Leopard. SerialNet also worked nicely on a WinXP laptop.


See the latest at

Startup Process

An approximation of how things begin:


Calls are made via the "arduino" object; arduino.js and .swf are the only two files needed. Parameters as shown below can be set either inline or externally, and are then referenced at init/onload() time.

arduino.config.flash.url = '/path/to/arduinojs.swf';

arduino.config.debug.enabled = true; // useful for connection setup/troubleshooting

arduino.config.debug.flash.showUI = true; // helps when fixing flash/onload() problems

// configuring pins by type: digitalIn, digitalOut, pwmOut, servo: see arduino.config.pins array

arduino.onload = function() {

  // Flash has loaded, now we're ready to connect to the proxy..

  arduino.connect('', '5331', function() { // host, port, "on connect..."

    // Yay, Arduino is now ready for I/O operations

    // write a high bit to digital pin 13, turn on built-in LED etc.
    arduino.writeDigitalPin(13, 1);

    // reading from digital inputs
    arduino.getDigitalData(<pin number>);

    // reading from analog inputs (0-5 on Arduino Uno, separate from digital pins)
    arduino.getAnalogData(<pin number>);

    // digital output
    a.writeDigitalPin(<pin number>, <0 or 1>);

    // pins configured with "PWM" type
    a.writeAnalogPin(<pin number>, <0 - 255>);

    // pins configured with "servo" type
    a.writeAnalogPin(<pin number>, <0-179>);



Reading Data: onReceiveData()-style Events vs. Polling

When reading data from the Arduino, you can either use a setInterval-based polling-style approach that regularly calls getAnalogData() / getDigitalData(), or assign event handlers which will fire when analog and digital data is received. Depending on your use case, the latter may be more efficient.

In either case, arduino.js caches data from all onReceiveData-type events in a local JS array, so user API calls to get data don't have to hit Flash.

// Event callbacks for analog/digital RX

arduino.onAnalogReceiveData = function(pinNumber, port, value) {

  console.log('Analog RX: pin ' + pinNumber + ' = ' + value + ', port: '+port);


arduino.onAnalogReceiveData = function(pinNumber, port, value) {

  console.log('Digital RX: pin ' + pinNumber + ' = ' + value + ', port: '+port);


// Alternate: Polling-style, read inputs at regular interval

function readData() {

  console.log('Pin 13 value: ' + arduino.getDigitalData(13));
  console.log('Analog input 0 value: ' + arduino.getAnalogData(0));


setInterval(readData, 250);

Note that analog data RX events may fire quite regularly due to electrical noise and fluctuating input values.

Pin Configuration

Pins can be set up according to available types (options): digitalIn, digitalOut, pwmOut or servo. The dedicated analog ports are analogIn only.

arduino.config.pins = [

  // - type --------- label ----------- options ---

  null,            // Pin 0         null (is RX)
  null,            // Pin 1         null (is TX)
  'digitalOut',    // Pin 2         digitalIn or digitalOut
  'digitalOut',    // Pin 3         pwmOut or digitalIn or digitalOut
  'digitalOut',    // Pin 4         digitalIn or digitalOut
  'digitalOut',    // Pin 5         pwmOut or digitalIn or digitalOut
  'digitalOut',    // Pin 6         pwmOut or digitalIn or digitalOut
  'digitalOut',    // Pin 7         digitalIn or digitalOut
  'digitalOut',    // Pin 8         digitalIn or digitalOut
  'pwmOut',        // Pin 9         pwmOut or digitalIn or digitalOut or servo
  'pwmOut',        // Pin 10        pwmOut or digitalIn or digitalOut or servo
  'pwmOut',        // Pin 11        pwmOut or digitalIn or digitalOut
  'digitalIn',     // Pin 12        digitalIn or digitalOut
  'digitalOut',    // Pin 13        digitalIn or digialOut (LED connected)

  // -- dedicated analog inputs (Arduino Uno) ------

  'analogIn',      // Analog pin 0  analogIn
  'analogIn',      // Analog pin 1  analogIn
  'analogIn',      // Analog pin 2  analogIn
  'analogIn',      // Analog pin 3  analogIn
  'analogIn',      // Analog pin 4  analogIn
  'analogIn'       // Analog pin 5  analogIn


The pin configuration array is applied when the arduino connection is established, after connect() and before the connect success handler.

Flash Troubleshooting

If you are viewing this page offline (non-HTTP eg. file:// or c:\ and so on), you may need to adjust the Flash Player Security Settings and allow this file as a "trusted" location.

Check the arduinojs.swf file and see if it mentions security-related messages. If so, hit up the Flash Player Global Security Settings panel. You will need to add the current location (Edit Locations -> Add Location -> Browse For Folder) and choose the current directory/folder in order for JS + Flash communication to work offline.

General Disclaimer

Of course, this is experimental; check arduino.js for the actual code, other API methods and comments.


arduino.js is an experiment by Scott Schiller.

This project would not have been possible without open-source code and libraries made available by other Arduino fans. See license.txt for details.