Ethernet Shield + Duemilanove Problems Unstable

Hello all,

I am experimenting for a while with an Arduino Server sketch and am hitting a wall.

I am using a Wiznet 5100, ethernet and dhcp libs. Power supply is 12V/300mA.

After initial issues with the Reset button and going through the many posts on the forum I finally settled for “bend” option connecting the RESET pin to an available Arduino pin (4) and added the necessary code in the setup() function.

#include <Ethernet.h>
#include <EthernetDHCP.h>

byte mac[] = { 0xDA, 0xAD, 0xBE, 0xAA, 0xFE, 0xED };


Server server = Server(80);

void setup()
  digitalWrite(WIZNET_RESET_PIN, LOW);
  digitalWrite(WIZNET_RESET_PIN, HIGH);
  if (EthernetDHCP.begin(mac) == 1) {

void loop() {
  Client client = server.available();
  if (client) {
    server.print("HTTP/1.0 200 OK\r\nServer: Arduino\r\nContent-Type: text/html\r\n\r\n");
    server.print("<b>Welcome to Arduino!</b>
    server.print("Uptime: ");
    server.print(" ms.</BODY></HTML>");

Unfortunately, after a few seconds of inactivity, the modules go into a state with “L” LED blinking and mad flickering of the TX/RX LEDs on the Arduino.

I had tried before the capacitor with one and two 100nF which didn’t work for me.

Could this be related to the watchdog timer or would I be luckier just ordering a new Ethernet shield? What concerns me is that the jumpering trick seems to have worked for most. Perhaps there’s also another problem with the code?

TIA for additional hints.

Not forced to be the issue, but a 12V supply isn't a good idea using an ethernet shield. The voltage regulator on the arduino will be getting hot, especially if its putting out more than 12V as many do. Do the problems still occur if you power it from USB ? The capacitor tricks are to get the board to startup after a reset / power outage, they don't improve the stability of the system.

Thanks! I understand - just wanted to indicate that my first problems were related to starting the shield. Now that I can start it, it doesn't stay on and goes into some funky whirl...

I can lower the voltage but I will eventually stack a Libelium GSM shield which requires 2A for GPRS operations. I could supply for now 6V/300mA - I'll try later. USB is not an option as it must work standalone.

6V isn't high enough for the regulator to supply 5V. 7V-9V should be OK. It could be the power supply doesn't have sufficient smoothing, which is a problem I've run into with an ethernet shield. They're greedy beggers and pull a lot more current than an Arduino. Couldn't you prove the setup on USB ? If it works on USB then its a power supply problem.

Why are you changing your wiznet reset pin to an input??? It should remain an output and be high when you want the shield to function.