problems when using ethernet shield

Hi everyone!

I have bought an ethernet shield and I´m having some problems when I try to use the digital pins:

As far as I know, the shield uses the pins 13,12,11 and 10 so it means that I can use the rest of them (2,3,4,5,6,7,8 and 9, I´ve an arduino UNO) but when I try to connect a sensor(that I have tested before) in one of theese pins it doesn´t work.

If I change the code and put as a coment the part of: "Ethernet.begin();" the sensor works wtih no problems.

I think it´s a problem of the shield but now the question is where/how can I study the shield schematic to be sure what all pins can i use. I cant believe that using the shield means sacrificing 13 of the digital pins !

What Ethernet shield are you using? The w5100 based shield may use pin 4 for some operations. The below server code controls pin 5, which you can observe with a multimeter.

//zoomkat 4-1-12
//simple button GET for servo and pin 5
//for use with IDE 1.0
//open serial monitor to see what the arduino receives
//use the \ slash to escape the " in the html, or use ' instead of " 
//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 control
  //enable serial data print 
  Serial.begin(9600); 
  Serial.println("server servo/pin 5 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("<a href=\"/?on1\">ON</a>"); 
          client.println("<a href=\"/?off\">OFF</a>"); 

          client.println("</BODY>");
          client.println("</HTML>");
 
          delay(1);
          //stopping client
          client.stop();

          ///////////////////// control arduino pin
          if(readString.indexOf("on1") >0)//checks for on
          {
            myservo.write(40);
            digitalWrite(5, HIGH);    // set pin 5 high
            Serial.println("Led On");
          }
          if(readString.indexOf("off") >0)//checks for off
          {
            myservo.write(140);
            digitalWrite(5, LOW);    // set pin 5 low
            Serial.println("Led Off");
          }
          //clearing string for next read
          readString="";

        }
      }
    }
  }
}