On Arduino Mega, Ethernet messes with AnalogRead values

Projects General Guidance
1

Hello,

I am having a problem that may be related to the Mega because I have never experienced it before. After I start the ethernet with Ethernet.begin every analog pin I read has a value in the mid 900s and I cannot read the input values.

For example,

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


static uint8_t ip[] = {     
  192, 168, 1, 99 };

static uint8_t mac[] = { 
  0x90, 0xA2, 0xDA, 0xAD, 0xAF, 0x77 };

 
void setup() { 
  Serial.begin(9600);

  //Ethernet.begin(mac, ip);

  pinMode(A14, INPUT);
}


void loop() {
    Serial.println(analogRead(A14));
}

Will return a variable value based on the potentiometer I have connected to pin A14.

But

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


static uint8_t ip[] = {     
  192, 168, 1, 99 };

static uint8_t mac[] = { 
  0x90, 0xA2, 0xDA, 0xAD, 0xAF, 0x77 };

 
void setup() { 
  Serial.begin(9600);

  Ethernet.begin(mac, ip);

  pinMode(A14, INPUT);
}


void loop() {
    Serial.println(analogRead(A14));
}

will return:

991
991
991
991
991
991
991
990
991
991
991
991
991
991
991
991
991

no matter where the pot is located.

I am sure it is something I am doing wrong. I have done this before on a smaller board and do not remember any issue like this.

Any help to point me in the right direction would be really help.

Mike

2

Have you tried other analog pins?

3

Why are you setting the digital nature of the pin when you are using it as an analog pin?

4

Some ethernet test code that includes reading the analog pin inputs. Note that the analog pins float with out a pot properly attached.

// zoomkat's meta refresh data frame test page 8/17/13
// use http://192.168.1.102:84 in your brouser for main page
// http://192.168.1.102:84/data static data page
// http://192.168.1.102:84/datastart meta refresh data page
// for use with W5100 based ethernet shields
// set the refresh rate to 0 for fastest update
// use STOP for single data updates

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

const int analogInPin0 = A0;
const int analogInPin1 = A1;
const int analogInPin2 = A2;
const int analogInPin3 = A3;
const int analogInPin4 = A4;
const int analogInPin5 = A5;

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; //physical mac address
byte ip[] = { 192, 168, 1, 102 }; // arduino 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
unsigned long int x=0; //set refresh counter to 0
String readString; 

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

void setup(){
  Serial.begin(9600);
    // disable SD SPI if memory card in the uSD slot
  pinMode(4,OUTPUT);
  digitalWrite(4,HIGH);

  Ethernet.begin(mac, ip, gateway, gateway, subnet);
  server.begin();
  Serial.println(F("meta refresh data frame test 8/17/13")); // so I can keep track of what is loaded
}

void loop(){
  EthernetClient client = server.available();
  if (client) {
    while (client.connected()) {
      if (client.available()) {
        char c = client.read();
         if (readString.length() < 100) {
          readString += c; 
         } 
        //check if HTTP request has ended
        if (c == '\n') {

          //check get atring received
          Serial.println(readString);

          //output HTML data header
          //client.println("HTTP/1.1 200 OK");
          //client.println("Content-Type: text/html");
          //client.println();
          
          client.print(F("HTTP/1.0 200 OK\r\nContent-Type: text/html\r\n\r\n"));

          //generate data page
          if(readString.indexOf("data") >0) {  //checks for "data" page
            x=x+1; //page upload counter
            client.print(F("<HTML><HEAD>"));
            //meta-refresh page every 1 seconds if "datastart" page
            if(readString.indexOf("datastart") >0) client.print(F("<meta http-equiv='refresh' content='1'>")); 
            //meta-refresh 0 for fast data
            if(readString.indexOf("datafast") >0) client.print(F("<meta http-equiv='refresh' content='0'>")); 
            client.print(F("<title>Zoomkat's meta-refresh test</title></head><BODY>
"));
            client.print(F("page refresh number: "));
            client.print(x); //current refresh count
            client.print(F("

"));
            
              //output the value of each analog input pin
            client.print(F("analog input0 is: "));
            client.print(analogRead(analogInPin0));
            
            client.print(F("
analog input1 is: "));
            client.print(analogRead(analogInPin1));
                        
            client.print(F("
analog input2 is: "));
            client.print(analogRead(analogInPin2));
            
            client.print(F("
analog input3 is: "));
            client.print(analogRead(analogInPin3));
                                    
            client.print(F("
analog input4 is: "));
            client.print(analogRead(analogInPin4));
            
            client.print(F("
analog input5 is: "));
            client.print(analogRead(analogInPin5));
            client.print(F("
</BODY></HTML>"));
           }
          //generate main page with iframe
          else
          {
            client.print(F("<HTML><HEAD><TITLE>Zoomkat's frame refresh test</TITLE></HEAD>"
            "Zoomkat's Arduino frame meta refresh test 8/17/13"
            "

Arduino analog input data frame:
"
            "&nbsp;&nbsp;<a href='/datastart' target='DataBox' title=''yy''>META-REFRESH</a>"
            "&nbsp;&nbsp;&nbsp;&nbsp;<a href='/data' target='DataBox' title=''xx''>SINGLE-STOP</a>"
            "&nbsp;&nbsp;&nbsp;&nbsp;<a href='/datafast' target='DataBox' title=''zz''>FAST-DATA</a>
"
            "<iframe src='/data' width='350' height='250' name='DataBox'>"
            "</iframe>
</HTML>"));
          }
          delay(1);
          //stopping client
          client.stop();
          //clearing string for next read
          readString="";
        }
      }
    }
  }
}