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Connection between Arduino and internet is possible with the Ethernet Shield W5100. The basis for creating connected objects, is to connect them over a network such as the WiFi network.
Communication via the Ethernet network is very convenient when you want to connect a device to Wifi.

For a wireless connection, you should use a Wifi Shield or another board with embedded Wifi chip


  • Computer
  • ArduinoUNO
  • USB A Male/B Male
  • Ethernet cable RJ45
  • Ethernet Shield W5100

Operating principle of an Ethernet Shield W5100

The communication network uses the Ethernet which can be linked to local Wifi network. To access the Arduino board without having to connect to the Internet router, it is necessary to create a bridge between wifi and ethernet connection in your computer. For this, we must:

  • Go to the Network and Sharing Center.
  • Go to “Change adapter settings”
  • Select Ethernet and Wifi/(internet source) and right click.
  • Click “Create Bridge”.

In Windows, the control terminal, type “arp -a” to see the IP addresses used on the network.

The Ethernet Shield W5100 uses Microchip W5100 as Ethernet controller.


The Ethernet Shield W5100 is compatible with the Arduino UNO and Mega microcontroller. The W5100 and SD card use the SPI bus to communicate with the Arduino board. The pin 10 is used to select the ethernet controller W5100, pin 9 as RESET to the W5100 and pin 4 to select the SD card module.

In summary, the pins used are:

  • 4 to select the SD card (SD_CS)
  • 9 for the reset of the W5100 microchip (W5100_RST)
  • 10 to select the W5100 microchip (W5100_CS)
  • SPI bus: 11,12,13 pins on an Arduino UNO board/Duelmilanove. The pins 50, 51 and 52 for the Mega

Code for an Ethernet Shield W5100

To communicate over the network, we need to use a particular protocol. This protocol is integrated in Arduino libraries dealing with WiFi communication.

  • You need to connect the WiFi module or Ethernet network
  • set a server
  • define a Customer
#include <Ethernet.h>//https://github.com/CisecoPlc/Arduino-W5100-W5200/tree/master/Ethernet

String request ;
unsigned long refreshCounter  = 0;
byte mac [6] = {0x54, 0x34, 0x41, 0x30, 0x30, 0x31};

EthernetServer server(80);
IPAddress ip(192, 168, 1, 179);
EthernetClient client;

void setup() {
  //Init Serial USB
  Serial.println(F("Initialize System"));
  //Init W5100
  Ethernet.begin(mac, ip);
  while (!Ethernet.begin(mac)) {
    Serial.println(F("failed. Retrying in 5 seconds."));
    Serial.print(F("Starting W5100..."));
  pinMode(2, OUTPUT);
  Serial.println(F("W5100 initialized"));
  Serial.print(F("IP Address: "));

void loop() {
  client = server.available();

void clientRequest( ) { /* function clientRequest */
  ////Get client request
  if (!client) {
  // Wait until the client sends some data
  while (!client.available()) {

  request = client.readStringUntil('\r'); // Read the first line of the request

void handleRequest( ) { /* function handleRequest */
  ////Handle web client request
  if (request.indexOf('GET') >= 0) {
  if (request.indexOf("/dig2on") > 0) {
      digitalWrite(2, HIGH);
  if (request.indexOf("/dig2off") > 0) {
      digitalWrite(2, LOW);

void webpage(EthernetClient client) { /* function webpage */
  ////Send webpage to client

  //output HTML data header
  client.println(F("HTTP/1.1 200 OK"));
  client.println(F("Content-Type: text/html"));
  client.print(F("<!DOCTYPE HTML><html><head><title>AranaCorp</title>"));
  client.print(F("<meta http-equiv='content-type' content='text/html; charset=UTF-8'>"));
  //meta-refresh page every x seconds
  client.print(F("<meta http-equiv='refresh' content='2'>"));
  client.print(F("</head><body bgcolor='black'><br>"));
  client.print(F("<h1 style='color : #3AAA35;'><center> AranaCorp - Arduino Web Controller </center></h1>"));
  client.print("<center><p style='color:white;'>");
  client.print(F("Page refresh number : "));
  client.print(refreshCounter); //current refresh count
  client.print(F("<h2 style='color:green;'>Arduino Inputs</h2>"));
  client.print("<p style='color:white;'>");

  //output analog input pin
  for (int i = 0; i < 6; i++) {
    client.print("<b>Input A");
    client.print(" : </b>");
    client.print(analogRead(14 + i)); //A0=14, A1=15 ,etc.

  //digital output
  client.print(F("<h2 style='color:green;'>Arduino Outputs</h2>"));
  client.print(F("<p style='color:white;'>"));
  client.print(F("<b>Digital output Pin 2 : </b>"));
  client.print("<input value=" + String(digitalRead(2)) + " readonly></input>");
  client.print(F("<a href='/dig2on'><button>Turn On </button></a>"));
  client.print(F("<a href='/dig2off'><button>Turn Off </button></a><br />"));


  //file end
  refreshCounter += 1;


We can see that the Ethernet Shield W5100 initializes correctly. When you enter the IP address in the browser address bar, the web page described in the function appears.
Once the page loads, the analog input values ​​vary with each refresh and the status of the pin 2 can be changed by pressing the corresponding buttons.


  • Use a web interface to control your Arduino


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