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 or Genuino 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.

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

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



 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[4];

void setup() {
  // initialize the Ethernet device
  Ethernet.begin(mac, ip, myDns, gateway, subnet);
  // start listening for clients
  // Open serial communications and wait for port to open:
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only

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

void loop() {
  // wait for a new client:
  EthernetClient client = server.available();

  // when the client sends the first byte, say hello:
  if (client) {

    boolean newClient = true;
    for (byte i = 0; i < 4; i++) {
      //check whether this client refers to the same socket as one of the existing instances:
      if (clients[i] == client) {
        newClient = false;

    if (newClient) {
      //check which of the existing clients can be overridden:
      for (byte i = 0; i < 4; i++) {
        if (!clients[i] && clients[i] != client) {
          clients[i] = client;
          // clear out the input buffer:
          Serial.println("We have a new client");
          client.print("Hello, client number: ");

    if (client.available() > 0) {
      // read the bytes incoming from the client:
      char thisChar =;
      // echo the bytes back to all other connected clients:
      for (byte i = 0; i < 4; i++) {
        if (clients[i] && (clients[i] != client)) {
      // echo the bytes to the server as well:
  for (byte i = 0; i < 4; i++) {
    if (!(clients[i].connected())) {
      // client.stop() invalidates the internal socket-descriptor, so next use of == will allways return false;

See also

Last revision 2015/08/13 by SM