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Simple Ethernet

This is the first in a series of Ethernet projects. This first project will display the values coming from the analog ports in a web browser on a remote machine. Additional posts will cover controlling the Arduino from a web browser, and reading and writing to the SD card for logging purposes. Stay tuned!

I popped a Arduino EtherShield SD on to an older Duemilanove (328), and loaded the following sketch. I changed the MAC address to the one printed on the bottom of my EtherShield, and put in a applicable IP address from my network. When I pointed my browser to the new IP address, I got the following output:

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analog input 0 is 1023
analog input 1 is 0
analog input 2 is 1023
analog input 3 is 771
analog input 4 is 551
analog input 5 is 437

This makes sense, because I have A0 and A2 connected to 5v, A1 connected to Gnd, and A3-A5 are left floating, and the values change every second or so.

Sketch from examples folder (Ethernet, Web Server)

Web Server

A simple web server that shows the value of the analog input pins.
using an Arduino Wiznet Ethernet shield.

* Ethernet shield attached to pins 10, 11, 12, 13
* Analog inputs attached to pins A0 through A5 (optional)

created 18 Dec 2009
by David A. Mellis
modified 9 Apr 2012
by Tom Igoe


#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:
byte mac[] = {
0x90, 0xA2, 0xDA, 0x00, 0x23, 0x36 };
IPAddress ip(192,168,254, 177);

// Initialize the Ethernet server library
// with the IP address and port you want to use
// (port 80 is default for HTTP):
EthernetServer server(80);

void setup() {
// Open serial communications and wait for port to open:
while (!Serial) {
; // wait for serial port to connect. Needed for Leonardo only

// start the Ethernet connection and the server:
Ethernet.begin(mac, ip);
Serial.print(“server is at “);

void loop() {
// listen for incoming clients
EthernetClient client = server.available();
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 =;
// 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(“Connnection: close”);
// add a meta refresh tag, so the browser pulls again every 5 seconds:
// 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(” is “);
“);          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
// close the connection:
Serial.println(“client disonnected”);

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