Problem Ethernet sheild HTML page

Hi all,
I am trying to do a very simple LED control using Ethernet shield based on wiznet W5100. The code works fine... some times.... mostly what happens is when i type in the IP address of the shield the page appears instantly some times it takes its sweet time i do power reset and reset then it start to work again. When the page does finally come up, i click on the radio button (on the page displayed by the arduino), the LED lights up and every thing is ok but i i keep playing with it as in press it then after a second press it again (kinda toggle action) the browser just keeps waiting for the response from the server (arduino). All this is connected on a local network. I tried other code but it has the same problems. Any help?

It could also be that I am connected to the router via a switch ?

/*--------------------------------------------------------------
  Program:      eth_websrv_LED

  Description:  Arduino web server that serves up a web page
                allowing the user to control an LED
  
  Hardware:     - Arduino Uno and official Arduino Ethernet
                  shield. Should work with other Arduinos and
                  compatible Ethernet shields.
                - LED and resistor in series connected between
                  Arduino pin 2 and GND
                
  Software:     Developed using Arduino 1.0.3 software
                Should be compatible with Arduino 1.0 +
  
  References:   - WebServer example by David A. Mellis and 
                  modified by Tom Igoe
                - Ethernet library documentation:
                  http://arduino.cc/en/Reference/Ethernet

  Date:         11 January 2013
 
  Author:       W.A. Smith, http://startingelectronics.com
--------------------------------------------------------------*/

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

// MAC address from Ethernet shield sticker under board
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(10, 0, 0, 20); // IP address, may need to change depending on network
EthernetServer server(80);  // create a server at port 80

String HTTP_req;          // stores the HTTP request
boolean LED_status = 0;   // state of LED, off by default

void setup()
{
    Ethernet.begin(mac, ip);  // initialize Ethernet device
    server.begin();           // start to listen for clients
    Serial.begin(9600);       // for diagnostics
    pinMode(2, OUTPUT);       // LED on pin 2
}

void loop()
{
    EthernetClient client = server.available();  // try to get client

    if (client) {  // got client?
        boolean currentLineIsBlank = true;
        while (client.connected()) {
            if (client.available()) {   // client data available to read
                char c = client.read(); // read 1 byte (character) from client
                HTTP_req += c;  // save the HTTP request 1 char at a time
                // last line of client request is blank and ends with \n
                // respond to client only after last line received
                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");
                    client.println();
                    // send web page
                    client.println("<!DOCTYPE html>");
                    client.println("<html>");
                    client.println("<head>");
                    client.println("<title>Arduino LED Control</title>");
                    client.println("</head>");
                    client.println("<body>");
                    client.println("<h1>LED</h1>");
                    client.println("<p>Click to switch LED on and off.</p>");
                    client.println("<form method=\"get\">");
                    ProcessCheckbox(client);
                    client.println("</form>");
                    client.println("</body>");
                    client.println("</html>");
                    Serial.print(HTTP_req);
                    HTTP_req = "";    // finished with request, empty string
                    break;
                }
                // every line of text received from the client ends with \r\n
                if (c == '\n') {
                    // last character on line of received text
                    // starting new line with next character read
                    currentLineIsBlank = true;
                } 
                else if (c != '\r') {
                    // a text character was received from client
                    currentLineIsBlank = false;
                }
            } // end if (client.available())
        } // end while (client.connected())
        delay(1);      // give the web browser time to receive the data
        client.stop(); // close the connection
    } // end if (client)
}

// switch LED and send back HTML for LED checkbox
void ProcessCheckbox(EthernetClient cl)
{
    if (HTTP_req.indexOf("LED2=2") > -1) {  // see if checkbox was clicked
        // the checkbox was clicked, toggle the LED
        if (LED_status) {
            LED_status = 0;
        }
        else {
            LED_status = 1;
        }
    }
    
    if (LED_status) {    // switch LED on
        digitalWrite(2, HIGH);
        // checkbox is checked
        cl.println("<input type=\"checkbox\" name=\"LED2\" value=\"2\" \
        onclick=\"submit();\" checked>LED2");
    }
    else {              // switch LED off
        digitalWrite(2, LOW);
        // checkbox is unchecked
        cl.println("<input type=\"checkbox\" name=\"LED2\" value=\"2\" \
        onclick=\"submit();\">LED2");
    }
}

Looks like you need to use that serial monitor for some debugging. I added some Serial.println() calls to your loop() code to try to figure out where it is failing. Look for "// add this" in the code.

void loop() {
    EthernetClient client = server.available();  // try to get client

    if (client) {  // got client?

// add this
        Serial.println(F("Client"));
     
        boolean currentLineIsBlank = true;
        while (client.connected()) {
            if (client.available()) {   // client data available to read
                char c = client.read(); // read 1 byte (character) from client
                HTTP_req += c;  // save the HTTP request 1 char at a time
                // last line of client request is blank and ends with \n
                // respond to client only after last line received
                if (c == '\n' && currentLineIsBlank) {

// add this
                    Serial.println(F("sending response"));               

                    // send a standard http response header
                    client.println("HTTP/1.1 200 OK");
                    client.println("Content-Type: text/html");
                    client.println("Connection: close");
                    client.println();
                    // send web page
                    client.println("<!DOCTYPE html>");
                    client.println("<html>");
                    client.println("<head>");
                    client.println("<title>Arduino LED Control</title>");
                    client.println("</head>");
                    client.println("<body>");
                    client.println("<h1>LED</h1>");
                    client.println("<p>Click to switch LED on and off.</p>");
                    client.println("<form method=\"get\">");
                    ProcessCheckbox(client);
                    client.println("</form>");
                    client.println("</body>");
                    client.println("</html>");
                    Serial.print(HTTP_req);
                    HTTP_req = "";    // finished with request, empty string
                    break;
                }
                // every line of text received from the client ends with \r\n
                if (c == '\n') {
                    // last character on line of received text
                    // starting new line with next character read
                    currentLineIsBlank = true;
                } 
                else if (c != '\r') {
                    // a text character was received from client
                    currentLineIsBlank = false;
                }
            } // end if (client.available())
        } // end while (client.connected())
        delay(1);      // give the web browser time to receive the data
        client.stop(); // close the connection

// add this
        Serial.println(F("disconnected"));

    } // end if (client)
}

When it fails and you have "Client" on the serial monitor but never get a "Sending response", I might be able to help you fix that.

I never use the String data type. It has been known to cause crashes. I use character arrays instead.

I also use the F() function to keep those static strings in program memory instead of loading them into SRAM. I used the F() function on the additions I did to the code. I recommend using that on all the static strings in your code.

Here is my server code. It shouldn't lock up.
http://playground.arduino.cc//Code/WebServerST

Some simple server code that controls an arduino pin and a servo. You can open the serial monitor to see what the arduino is receiving.

//zoomkat 3-1-12
//simple button GET for pin and servo control
//for use with IDE 1.0
//open serial monitor to see what the arduino receives
//use the \ slash to escape the " in the html 
//address will look like http://192.168.1.102:84 when submited
//for use with W5100 based ethernet shields

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

#include <Servo.h> 
Servo myservo;  // create servo object to control a servo 

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; //physical mac address
byte ip[] = { 192, 168, 1, 102 }; // ip in lan
byte gateway[] = { 192, 168, 1, 1 }; // internet access via router
byte subnet[] = { 255, 255, 255, 0 }; //subnet mask
EthernetServer server(84); //server port

String readString; 

//////////////////////

void setup(){

  pinMode(5, OUTPUT); //pin selected to control
  //start Ethernet
  Ethernet.begin(mac, ip, gateway, gateway, subnet);
  server.begin();

  myservo.write(90); //set initial servo position if desired
  myservo.attach(7);  //the pin for the servo co
  //enable serial data print 
  Serial.begin(9600); 
  Serial.println("server LED test 1.0"); // so I can keep track of what is loaded
}

void loop(){
  // Create a client connection
  EthernetClient client = server.available();
  if (client) {
    while (client.connected()) {
      if (client.available()) {
        char c = client.read();

        //read char by char HTTP request
        if (readString.length() < 100) {

          //store characters to string 
          readString += c; 
          //Serial.print(c);
        } 

        //if HTTP request has ended
        if (c == '\n') {

          ///////////////
          Serial.println(readString); //print to serial monitor for debuging 

          client.println("HTTP/1.1 200 OK"); //send new page
          client.println("Content-Type: text/html");
          client.println();

          client.println("<HTML>");
          client.println("<HEAD>");
          client.println("<TITLE>Arduino GET test page</TITLE>");
          client.println("</HEAD>");
          client.println("<BODY>");

          client.println("<H1>Zoomkat's simple Arduino button</H1>");
          
          client.println("
<input type=\"button\" value=\"ON\" onmousedown=\"location.href ('/?on');\"/>"); 
          client.println("<input type=\"button\" value=\"OFF\" onmousedown=\"location.href ('/?off');\"/>");        
 
          client.println("</BODY>");
          client.println("</HTML>");
 
          delay(1);
          //stopping client
          client.stop();

          ///////////////////// control arduino pin
          if(readString.indexOf("on") >0)//checks for on
          {
            myservo.write(40);
            digitalWrite(5, HIGH);    // set pin 4 high
            Serial.println("Led On");
          }
          if(readString.indexOf("off") >0)//checks for off
          {
            myservo.write(140);
            digitalWrite(5, LOW);    // set pin 4 low
            Serial.println("Led Off");
          }
          //clearing string for next read
          readString="";

        }
      }
    }
  }
}

Keep in mind that every time you connect from a host computer to the arduino over USB, it resets the Arduino. This results in very erratic behavior and created a big headache for us until we discovered THAT little gem. Now we don't use serial at all and the world is round once again. There are a couple of hardware fixes for this "feature", find them w/ Google.

Peace,
Tyler

ZenSkunkworx:
Keep in mind that every time you connect from a host computer to the arduino over USB, it resets the Arduino.

That only happens when the application on the host computer opens/closes the serial port.