Arduino Ethernet Board Programming and Using

Created on: 24 June 2013
Updated on: 24 February 2023

The Arduino Ethernet board is like an Arduino Uno and Ethernet shield, but without USB. This article shows how to program, test and use the Arduino Ethernet board and what accessories are needed.

Take note that since this article was originally written (in 2013), the official Arduino Ethernet board is no longer available and is marked as 'retired' on the Arduino website. It can be replaced by an Arduino Uno and Ethernet shield. Find the official Arduino documentation for the Arduino Ethernet board on the Arduino Ethernet Rev3 without PoE – retired product page on the Arduino website.

In addition to the retired Arduino Ethernet board, the USB2SERIAL board used to program it is also retired. Find information on the USB2SERIAL board on the Arduino USB 2 Serial Micro – retired product page on the Arduino website.

Arduino Ethernet Board and Essential Accessories

Arduino Ethernet Board

The Arduino Ethernet board is shown below. It has an RJ45 Ethernet connector, power connector, connector for an external USB board for programming and micro SD card socket.

It is important to note that the board does not have USB on-board.

Arduino Ethernet board
Arduino Ethernet Board


An external USB to serial board is required to program the Arduino Ethernet board, such as the Arduino USB2SERIAL board.

The USB2SERIAL board also supplies power to the Arduino Ethernet board so that no external power is required while developing software and while the USB2SERIAL board is plugged in.

USB2SERIAL Arduino board
USB2SERIAL Arduino Board

Mini USB Cable

The USB2SERIAL board connects to a host computer using a USB Mini Cable. The USB Mini Cable has a miniature connector unlike the standard USB cable required for the Arduino Uno.

USB mini cable
USB Mini Cable

Uses of the Arduino Ethernet Board

The Arduino Ethernet board is suited to applications where an Arduino Uno and Ethernet shield would be used, but the USB connection is not needed.

The best cost saving would be reached if more than one Ethernet board is needed in a project. A single Arduino Ethernet can then be used to replace an Arduino Uno / Ethernet Shield combo. Only one USB2SERIAL would be needed to program all Arduino Ethernet boards for the project.

Testing the Arduino Ethernet Board

After getting an Arduino Ethernet board and USB2SERIAL board, you may want to test them before using them in a project.

Before loading any sketch to the Arduino Ethernet board, remember to select Arduino Ethernet under Tools → Board in the Arduino IDE software.

Programming / LED Test

The first and most basic test is to run the Blink example program found under File → Examples → 01.Basics → Blink in the Arduino IDE.

Loading and running the Blink sketch will test that you can upload sketches to the Arduino Ethernet board and test the LED.

Before running the Blink sketch, you will need to modify it because the LED is found on pin 9 of the Arduino Ethernet board and not on pin 13 like the Arduino Uno.

You can modify the sketch from the IDE or copy the modified Blink sketch below and paste it into the Arduino IDE.

  Turns on an LED on for one second, then off for one second, repeatedly.
  This example code is in the public domain.
// Pin 13 has an LED connected on most Arduino boards.
// give it a name:
int led = 9;  // *** changed to pin 9 for the Arduino Ethernet Board ***

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.
  pinMode(led, OUTPUT);     

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);               // wait for a second

Testing the Ethernet Connection

Do the same test as shown in the article on plugging in and testing the Arduino Ethernet shield.

You will of course need to plug the USB2SERIAL board into the Arduino Ethernet board to load the sketch and do the test.

Testing the Micro SD Card

To test a micro SD card and card socket on the Arduino Ethernet board, do the same tests as shown in the article on testing the SD card on the Arduino Ethernet shield, but use the Arduino Ethernet board with USB2SERIAL board plugged in.