AdvancedChat Server

A more sophisticated server that distributes any incoming messages to all connected clients except the one that is sending the message. To use, open a terminal window, Telnet to your devices IP address, and type away. Any incoming text will be sent to all connected clients (including the one typing). Additionally, you will be able to see the client's input in your serial monitor as well.

Hardware Required


The Ethernet shield allows you to connect a WizNet Ethernet controller to the Arduino boards via the SPI bus. It uses pins 10, 11, 12, and 13 for the SPI connection to the WizNet. Later models of the Ethernet shield also have an SD Card on board. Digital pin 4 is used to control the slave select pin on the SD card.

The shield should be connected to a network with an ethernet cable. You will need to change the network settings in the program to correspond to your network.

EthernetShieldF bb

image developed using Fritzing. For more circuit examples, see the Fritzing project page

In the above image, the Arduino board would be stacked below the Ethernet shield.


EthernetShield sch



 Advanced Chat Server

 A more advanced server that distributes any incoming messages

 to all connected clients but the client the message comes from.

 To use, telnet to your device's IP address and type.

 You can see the client's input in the serial monitor as well.

 Using an Arduino Wiznet Ethernet shield.


 * Ethernet shield attached to pins 10, 11, 12, 13

 created 18 Dec 2009

 by David A. Mellis

 modified 9 Apr 2012

 by Tom Igoe

 redesigned to make use of operator== 25 Nov 2013

 by Norbert Truchsess


#include <SPI.h>
#include <Ethernet.h>

// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network.
// gateway and subnet are optional:
byte mac[] = {

  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED

IPAddress ip(192, 168, 1, 177);

IPAddress myDns(192, 168, 1, 1);

IPAddress gateway(192, 168, 1, 1);

IPAddress subnet(255, 255, 0, 0);

// telnet defaults to port 23

EthernetServer server(23);

EthernetClient clients[8];

void setup() {

  // You can use Ethernet.init(pin) to configure the CS pin

  //Ethernet.init(10);  // Most Arduino shields

  //Ethernet.init(5);   // MKR ETH shield

  //Ethernet.init(0);   // Teensy 2.0

  //Ethernet.init(20);  // Teensy++ 2.0

  //Ethernet.init(15);  // ESP8266 with Adafruit Featherwing Ethernet

  //Ethernet.init(33);  // ESP32 with Adafruit Featherwing Ethernet

  // initialize the Ethernet device

  Ethernet.begin(mac, ip, myDns, gateway, subnet);

  // Open serial communications and wait for port to open:


  while (!Serial) {

    ; // wait for serial port to connect. Needed for native USB port only


  // Check for Ethernet hardware present

  if (Ethernet.hardwareStatus() == EthernetNoHardware) {

    Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");

    while (true) {

      delay(1); // do nothing, no point running without Ethernet hardware



  if (Ethernet.linkStatus() == LinkOFF) {

    Serial.println("Ethernet cable is not connected.");


  // start listening for clients


  Serial.print("Chat server address:");


void loop() {

  // check for any new client connecting, and say hello (before any incoming data)

  EthernetClient newClient = server.accept();

  if (newClient) {

    for (byte i=0; i < 8; i++) {

      if (!clients[i]) {

        Serial.print("We have a new client #");


        newClient.print("Hello, client number: ");


        // Once we "accept", the client is no longer tracked by EthernetServer

        // so we must store it into our list of clients

        clients[i] = newClient;





  // check for incoming data from all clients

  for (byte i=0; i < 8; i++) {

    if (clients[i] && clients[i].available() > 0) {

      // read bytes from a client

      byte buffer[80];

      int count = clients[i].read(buffer, 80);

      // write the bytes to all other connected clients

      for (byte j=0; j < 8; j++) {

        if (j != i && clients[j].connected()) {

          clients[j].write(buffer, count);





  // stop any clients which disconnect

  for (byte i=0; i < 8; i++) {

    if (clients[i] && !clients[i].connected()) {

      Serial.print("disconnect client #");





See also

Last revision 2018/08/23 by SM