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WebJack-Firmata a wrapper for WebJack to use as transport layer for firmata.js. WebJackPort is inspired by EtherPort from Rick Waldron.

Live Demos

Try it out here:

Keyboard Bindings

A second example, showing triggering of Arduino pins via keyboard keypresses, is available at

Find build instructions for the demo at the end of this page.

Serial communication

A third example implements serial communication via firmata's serialWrite, but depends on StandardFirmataPlus.ino, which has not yet been ported over to be WebJack compatible. This could allow webjack-firmata to act as a serial bridge.


To install on your Arduino, see "Sketches" below.

To install on the browser side, you can use NPM:

npm install --save webjackport


var Firmata = require("firmata").Board;
var WebJackPort = require("webjackport");
var board = new Firmata(new WebJackPort());

board.on("ready", function() {
  console.log( + "-" +
    board.firmware.version.major + "." +

  var state = 1;

  this.pinMode(13, this.MODES.OUTPUT);

  setInterval(function() {
    this.digitalWrite(13, (state ^= 1));
  }.bind(this), 500);

Also take a look at the demo site in the example folder.


Three example sketches are provided:

  • SimpleDigitalFirmata
  • ConfigurableFirmata
  • StandardFirmataWebJack

SimpleDigitalFirmata and ConfigurableFirmata are capable of setting and reading digital pins. The first one is implemented with the standard Firmata library, the latter with ConfigureableFirmata.

StandardFirmataWebJack is a modification of the standard Firmata firmware and thus has all its capabilities. Additionally a custom SysEx command is implemented, that reports exactly one analog reading.

All sketches are configured with a 10 millisecond delay in the processing loop. This is due to crosstalk from requests messages. An immediate reply will make it difficult for WebJack to distinguish the crosstalk from the actual reply.

Arduino Create

You can use these sketches in the online Arduino editor at:

Known Issues

Currently, it is required to create the board with additional options:

var opts = {
  reportVersionTimeout: 2500,  // increase if no sound is played after loading the site
  skipCapabilities: true  // we skip this for now, reception via WebJack is not reliable enough
var board = new Board(new WebJackPort(), opts);

Audio cables may introduce crosstalk that can lead to reception of sent data. As a result of that, firmata can have difficulties to decode answers correctly. It can help to assign empty handler functions to SysEx requests as workaround:

board.sysexResponse(CAPABILITY_QUERY, function (data){});


Help improve Public Lab software!


webjackport.js is built using a Grunt task from the source files in /src/, and the compiled file is saved to /dist/webjackport.js. To build, run grunt build. To watch files for changes, and build whenever they occur, run grunt.

Building the demo

The demos in /example/ are bundled with Webpack. Before executing webpack, do npm install -- and cd example -- since you have to run webpack from inside the example directory. The code in /example/bundle.js, is then compiled from /example/Demo.js.


A wrapper for WebJack to use as transport layer for firmata.js, for firmata access to an Arduino from a web browser.




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