To disable the SD card:

pinMode(4,OUTPUT);
digitalWrite(4, HIGH);

To disable the Ethernet Controller chip:

pinMode(10,OUTPUT);
digitalWrite(10, HIGH);

Plug your Ethernet shield into your Arduino board using soldered wire wrap headers:

Fritzing representation of Arduino and Ethernet shield stack

Get the Ethernet cable and connect one end to the Ethernet jack of the Arduino Ethernet Shield.

One end of the Ethernet cable is connected to the Arduino Ethernet board

Connect the other end of the Ethernet cable to the Ethernet jack of the network router or switch.

The other end of the Ethernet cable is connected to the router/switch

Connect the 9VDC wall adapter power supply to the DC barrel connector of the Arduino board.

Use the USB A-to-B cable to connect your Arduino board to the computer. Connect the type A plug end to the computer and the type B plug end to the Arduino board.

One end of the Ethernet cable is connected to the Ethernet shield (top) and the power connector and USB cable are connected to the Arduino board (bottom) Image courtesy of SparkFun Electronics (https://www.sparkfun.com)

Open your Arduino IDE and navigate to File | Examples | Ethernet | WebServer:

The sample sketch WebServer will open in a new Arduino IDE:

You can also paste the code from the sketch named B04844_01_01.ino from the code folder of this chapter. The following header files should be included for serial communication and Ethernet communication in the beginning of the sketch:

#include <SPI.h> //initiates Serial Peripheral Interface
#include <Ethernet.h> //initiates Arduino Ethernet library

Replace the MAC address with your Ethernet shield's MAC address if you know it. You can find the printed sticker of the MAC address affixed to the back of your Ethernet shield. (Some clones of Arduino Ethernet Shield don't ship with a MAC address affixed on them). If you don't know the MAC address of your Arduino Ethernet Shield, use the one mentioned in the sample code or replace it with a random one. But don't use network devices with the same MAC address on your network; it will cause conflicts and your Ethernet shield will not function correctly. (Read Finding the MAC address and obtaining a valid IP address for more information on MAC addresses).

byte mac[] = {0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};

Replace the IP address with a static IP in your local network IP range. (Read the Finding the MAC address and obtaining a valid IP address section for selecting a valid IP address).

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

Then, create an instance of the Arduino Ethernet Server library and assign port number 80 to listen to incoming HTTP requests.

EthernetServer server(80);

Inside the setup() function, open the serial communications and wait for the port to open. The computer will communicate with Arduino at a speed of 9600 bps.

Serial.begin(9600);

The following code block will start the Ethernet connection by using the MAC address and IP address (we have assigned a static IP address) of the Arduino Ethernet Shield and start the server. Then it will print the IP address of the server on Arduino Serial Monitor using Ethernet.localIP():

Ethernet.begin(mac, ip);
server.begin();
Serial.print("server is at ");
Serial.println(Ethernet.localIP());

Inside the loop() function, the server will listen for incoming clients.

EthernetClient client = server.available();

If a client is available, the server will connect with the client and read the incoming HTTP request. Then, reply to the client by the standard HTTP response header. The output can be added to the response header using the EthernetClient class's println() method:

  if (client) {
    Serial.println("new client");
    // an http request ends with a blank line
    boolean currentLineIsBlank = true;
    while (client.connected()) {
      if (client.available()) {
        char c = client.read();
        Serial.write(c);
        // if you've gotten to the end of the line (received a newline
        // character) and the line is blank, the http request has ended,
        // so you can send a reply
        if (c == '\n' && currentLineIsBlank) {
          // send a standard http response header
          client.println("HTTP/1.1 200 OK");
          client.println("Content-Type: text/html");
          client.println("Connection: close");  // the connection will be closed after completion of the response
          client.println("Refresh: 5");  // refresh the page automatically every 5 sec
          client.println();
          client.println("<!DOCTYPE HTML>");
          client.println("<html>");
          // output the value of each analog input pin
          for (int analogChannel = 0; analogChannel < 6; analogChannel++) {
            int sensorReading = analogRead(analogChannel);
            client.print("analog input ");
            client.print(analogChannel);
            client.print(" is ");
            client.print(sensorReading);
            client.println("<br />");
          }
          client.println("</html>");
          break;
        }
        if (c == '\n') {
          // you're starting a new line
          currentLineIsBlank = true;
        }
        else if (c != '\r') {
          // you've gotten a character on the current line
          currentLineIsBlank = false;
        }
      }
    }
    // give the web browser time to receive the data
    delay(1);

Finally, close the connection from the client using the EthernetClient class's stop() method:

client.stop();
Serial.println("client disconnected");

Verify the sketch by clicking on the Verify button located in the toolbar.

On the menu bar, select the board by navigating to Tools | Board | Arduino UNO. If you are using an Arduino Ethernet board, select Tools | Board | Arduino Ethernet.

On the menu bar, select the COM port by navigating to Tools | Port and then selecting the port number.

Upload the sketch into your Arduino UNO board by clicking on the Upload button located in the toolbar.

Open your Internet browser (such as Google Chrome, Mozilla Firefox, or Microsoft Internet Explorer) and type the IP address (http://192.168.1.177/) assigned to your Arduino Ethernet Shield in the sketch (in Step 4), and hit the Enter key.

The web browser will display analog input values (impedance) of all the six analog input pins (A0-A5). The browser will refresh every 5 seconds with the new values. Use following code to change the automatic refresh time in seconds:

client.println("Refresh: 5");

Output for Arduino Ethernet board: Analog input values are displaying on the Google Chrome browser, refreshing every 5 seconds

Output for Arduino UNO + Arduino Ethernet Shield: Analog input values are displaying on the Google Chrome browser, refreshing every 5 seconds

Arduino Serial Monitor prints the static IP address of Arduino Ethernet Shield

To make your sketch more stable and to ensure that it does not hang, you can do one of the following: