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firmata4j is a client library of Firmata written in Java. The library allows controlling Arduino (or another board) which runs Firmata protocol from your java program.


  • Interaction with a board and its pins in object-oriented style
  • Abstraction over details of the protocol
  • Provides an UI component that visualize the current state of every pin and allows changing their mode and state
  • Allows communicating with I2C devices



Add the following dependency to pom.xml of your project:



General scenario of usage is following:

IODevice device = new FirmataDevice("/dev/ttyUSB0"); // construct the Firmata device instance using the name of a port
// subscribe to events using device.addEventListener(...);
// and/or device.getPin(n).addEventListener(...);
device.start(); // initiate communication to the device
device.ensureInitializationIsDone(); // wait for initialization is done
// sending commands to the board
device.stop(); // stop communication to the device

Sending commands to the board may cause the device to emit events. Registered listeners process the events asynchronously. You can add and remove listeners along the way.

You can subscribe to events of the device or its pin.

device.addEventListener(new IODeviceEventListener() {
    public void onStart(IOEvent event) {
        // since this moment we are sure that the device is initialized
        // so we can hide initialization spinners and begin doing cool stuff
        System.out.println("Device is ready");

    public void onStop(IOEvent event) {
        // since this moment we are sure that the device is properly shut down
        System.out.println("Device has been stopped");

    public void onPinChange(IOEvent event) {
        // here we react to changes of pins' state
        Pin pin = event.getPin();
                    "Pin %d got a value of %d",

    public void onMessageReceive(IOEvent event, String message) {
        // here we react to receiving a text message from the device

To obtain more fine grained control you can subscribe to events of a particular pin.

Pin pin = device.getPin(2);
pin.addEventListener(new PinEventListener() {
    public void onModeChange(IOEvent event) {
        System.out.println("Mode of the pin has been changed");

    public void onValueChange(IOEvent event) {
        System.out.println("Value of the pin has been changed");

You can change the mode and value of a pin:

pin.setMode(Pin.Mode.OUTPUT); // our listeners will get event about this change
pin.setValue(1); // and then about this change

You can get visual representation of device's pins using JPinboard Swing component.

JPinboard pinboard = new JPinboard(device);
JFrame frame = new JFrame("Pinboard Example");

JPinboard allows setting the pin's mode by choosing one from a context menu of the pin. State of the output pin can be changed by double clicking on it.

An example of JPinboard usage can be found in org.firmata4j.Example class.


firmata4j supports working with I2C devices. You can obtain a reference to an I2C device in this way:

IODevice device = new FirmataDevice(port);
byte i2cAddress = 0x3C;
I2CDevice i2cDevice = device.getI2CDevice(i2cAddress);

You may find convenient writing a wrapper for I2CDevice class to facilitate communication with I2C device. Consider SSD1306 and I2CExample classes as an example of that approach.


firmata4j sticks to Firmata protocol versions. The first available version of firmata4j is 2.3.1.

firmata4j-2.3.x will work well with Fimata v. 2.3.x. Actually it should work with Firmata v. 2.x.x but not necessarily support all of the protocol features. The first digits of versions must be equal because those stand for incompatible changes of the protocol.

Uploading Firmata To Arduino

Arduino IDE is shipped with an implementation of Firmata protocol. You can upload it as follows:

  • Plug your Arduino to the computer
  • Launch Arduino IDE
  • Select File -> Examples -> Firmata -> StandardFirmata in IDE's menu
  • Select your board in Tools -> Board
  • Select the port in Tools -> Port (it is already selected if you have uploaded something to your Arduino)
  • Click on Upload button



Contributions are welcome. If you discover a bug or would like to propose a new feature, please, open a new issue.

If you have an improvement to share, please, do the following:

  1. Fork this repository
  2. Clone your own fork to your machine (git clone<your_username>/firmata4j.git)
  3. Create a feature branch (git checkout -b my-new-feature)
  4. Change the code
  5. Commit the changes (git commit -am 'Adds some feature')
  6. Push to the branch (git push origin my-new-feature)
  7. Create new Pull Request


firmata4j is distributed under the terms of the MIT License. See the LICENSE file.