Starting Electronics needs your help! Please make a donation to help cover our hosting and other costs. Click the donate button to send a donation of any amount.

Find the Port Number that Arduino is Plugged Into

Created on: 6 November 2012

In this article, the serial port name / number is determined programmatically using the Processing language. This means that an application written in Processing is used to find and display the computer port name that Arduino or other USB serial device is plugged into.

This application has been tested on both Windows and Linux. Processing is available for Linux, Windows and Mac.

What the Application Does

Start with the Arduino unplugged. The application written in Processing first finds all the serial ports and USB serial ports on the system and stores them. It then waits for the Arduino to be plugged in.

When the Arduino is plugged in, it finds all the serial and USB ports on the computer again. It now determines what the serial port number is by finding the difference between the initial serial ports and the new set of serial ports.

Because the Arduino has been plugged in, there will now be a new serial port on the computer which the Processing application will find.

The port_find Processing Application Waiting for Arduino to be Plugged In
The port_find Processing Application Waiting for Arduino to be Plugged In
Arduino Port Found on a Linux System
Arduino Port Found on a Linux System

Books that may interest you:

C Programming with Arduino Book Ultimate Arduino MEGA 2560 Hardware Manual Ultimage Arduino Uno Hardware Manual

The Source Code

The listing for the Processing port_find sketch is shown below. It can be copied and pasted into the Processing IDE and run from there.

Alternatively, download the processing code (

The port_find Sketch in the Processing IDE
The port_find Sketch in the Processing IDE
  Program:      port_find

  Date:         1 November 2012
  Author:       W.A. Smith,
import processing.serial.*;

Serial ser_port;                // for serial port
PFont fnt;                      // for font
int num_ports;
boolean device_detected = false;
String[] port_list;
String detected_port = "";

void setup() {
    size(400, 200);                         // size of application window
    background(0);                          // black background
    fnt = createFont("Arial", 16, true);    // font displayed in window
    // get the number of detected serial ports
    num_ports = Serial.list().length;
    // save the current list of serial ports
    port_list = new String[num_ports];
    for (int i = 0; i < num_ports; i++) {
        port_list[i] = Serial.list()[i];

void draw()
    // display instructions to user
    textFont(fnt, 14);
    text("1. Arduino or serial device must be unplugged.", 20, 30);
    text("   (unplug device and restart this application if not)", 20, 50);
    text("2. Plug the Arduino or serial device into a USB port.", 20, 80);
    // see if Arduino or serial device was plugged in
    if ((Serial.list().length > num_ports) && !device_detected) {
        device_detected = true;
        // determine which port the device was plugge into
        boolean str_match = false;
        if (num_ports == 0) {
            detected_port = Serial.list()[0];
        else {
            // go through the current port list
            for (int i = 0; i < Serial.list().length; i++) {
                // go through the saved port list
                for (int j = 0; j < num_ports; j++) {
                    if (Serial.list()[i].equals(port_list[j])) {
                    if (j == (num_ports - 1)) {
                        str_match = true;
                        detected_port = Serial.list()[i];
    // calculate and display serial port name
    if (device_detected) {
        text("Device detected:", 20, 110);
        textFont(fnt, 18);
        text(detected_port, 20, 150);

New Book: Explore ATtiny Microcontrollers using C and Assembly Language

Explore ATtiny Microcontrollers using C and Assembly Language book Ultimate Arduino Uno Hardware Manual

As an Amazon Associate I earn from qualifying purchases: