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Serial Port Selection in a Processing Application

Created on: 21 July 2015

Scroll through a list of serial ports available on a PC and connect to the selected one from an application written in the Processing language (

The Processing application sketch below uses up and down buttons to scroll through the list of available serial ports. The Connect button is used to connect to the selected serial port. The Disconnect button disconnects the application from the currently open serial port. A Refresh button updates the list of serial ports and is used in case a serial device is plugged into the PC after the application was started.

This method of graphically selecting a serial port from within the Processing application window is an alternative to hard-coding the serial port number into the application.

The sketch can be used to add serial port selection capabilities to any Processing application for the purpose of communicating with serial devices such as Arduino.

In the video below, the application can be seen connecting to two Arduino boards on a Windows system. The Processing sketch has also been tested on a Linux system.

Can't see the video? View on YouTube →

Processing Code for Serial Port Selection

The code below can be used as a starting point for any Processing application that needs the ability for the user to select the serial port to connect to.

   Program:     port_select

   Description: Allows a serial port to be selected and connected to graphically.
                Has the following buttons:
                Up         - scrolls up through the serial port list 
                Down       - scrolls down through the serial port list
                Connect    - connects to the selected serial port
                Disconnect - disconnects from the serial port allowing a new serial
                             port to be connected to
                Refresh    - refreshes the list of serial ports. Useful if a new
                             serial device is connected to the PC after this app-
                             lication is started
   Purpose:     Allows the serial port to be selected within an application instead
                of hard-coding the port number
   Hardware:    Can be used to connect to Arduino or other serial devices
   Software:    Developed using Processing 2.2.1 (
                Uses the Button class from:
   Date:        21 July 2015   Author:   W.A. Smith,

import processing.serial.*;

Serial serial_port = null;        // the serial port

// serial port buttons
Button btn_serial_up;              // move up through the serial port list
Button btn_serial_dn;              // move down through the serial port list
Button btn_serial_connect;         // connect to the selected serial port
Button btn_serial_disconnect;      // disconnect from the serial port
Button btn_serial_list_refresh;    // refresh the serial port list
String serial_list;                // list of serial ports
int serial_list_index = 0;         // currently selected serial port 
int num_serial_ports = 0;          // number of serial ports in the list

void setup() {
  // set the window size
  size (640, 480);
  // create the buttons
  btn_serial_up = new Button("^", 140, 10, 40, 20);
  btn_serial_dn = new Button("v", 140, 50, 40, 20);
  btn_serial_connect = new Button("Connect", 190, 10, 100, 25);
  btn_serial_disconnect = new Button("Disconnect", 190, 45, 100, 25);
  btn_serial_list_refresh = new Button("Refresh", 190, 80, 100, 25);
  // get the list of serial ports on the computer
  serial_list = Serial.list()[serial_list_index];
  // get the number of serial ports in the list
  num_serial_ports = Serial.list().length;

void mousePressed() {
  // up button clicked
  if (btn_serial_up.MouseIsOver()) {
    if (serial_list_index > 0) {
      // move one position up in the list of serial ports
      serial_list = Serial.list()[serial_list_index];
  // down button clicked
  if (btn_serial_dn.MouseIsOver()) {
    if (serial_list_index < (num_serial_ports - 1)) {
      // move one position down in the list of serial ports
      serial_list = Serial.list()[serial_list_index];
  // Connect button clicked
  if (btn_serial_connect.MouseIsOver()) {
    if (serial_port == null) {
      // connect to the selected serial port
      serial_port = new Serial(this, Serial.list()[serial_list_index], 9600);
  // Disconnect button clicked
  if (btn_serial_disconnect.MouseIsOver()) {
    if (serial_port != null) {
      // disconnect from the serial port
      serial_port = null;
  // Refresh button clicked
  if (btn_serial_list_refresh.MouseIsOver()) {
    // get the serial port list and length of the list
    serial_list = Serial.list()[serial_list_index];
    num_serial_ports = Serial.list().length;

void draw() {
  // draw the buttons in the application window
  // draw the text box containing the selected serial port
  DrawTextBox("Select Port", serial_list, 10, 10, 120, 60);

// function for drawing a text box with title and contents
void DrawTextBox(String title, String str, int x, int y, int w, int h)
  rect(x, y, w, h);
  text(title, x + 10, y + 10, w - 20, 20);
  text(str, x + 10, y + 40, w - 20, h - 10);

// button class used for all buttons
class Button {
  String label;
  float x;    // top left corner x position
  float y;    // top left corner y position
  float w;    // width of button
  float h;    // height of button
  // constructor
  Button(String labelB, float xpos, float ypos, float widthB, float heightB) {
    label = labelB;
    x = xpos;
    y = ypos;
    w = widthB;
    h = heightB;
  // draw the button in the window
  void Draw() {
    rect(x, y, w, h, 10);
    textAlign(CENTER, CENTER);
    text(label, x + (w / 2), y + (h / 2));
  // returns true if the mouse cursor is over the button
  boolean MouseIsOver() {
    if (mouseX > x && mouseX < (x + w) && mouseY > y && mouseY < (y + h)) {
      return true;
    return false;


The Button class used in the above processing sketch is from the (no longer available) simple button for Processing language code blog article.

An alternative way of connecting to the serial port is to start the Processing application and then plug the serial device in. A Processing sketch can be used to find the serial port number of the newly plugged in device.

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