Monday, November 22, 2010

Arduino Wiznet ethernet shield proper reset

 Arduino 2009 Wiznet Ethernet Shield proper reset
 (last modified on nov 22 2010)

Problem: Arduino 2009 with wiznet w5100 ethernet shield does not start network operations after power-up.
It works well if the reset button is pressed.

Solution: I implemented davekw7x's suggestions (THANK YOU!), as cited in this arduino forum page (ref. reply #11)
this solution requires a 10kOhm resistor, and a 10nf capacitor.

Here are the detailed steps and some pictures:

1. bend outwards the ethernet shield reset pin "leg", so that it will not go in the arduino reset socket.
2. solder the 10kOhm resistor between reset pin and the nearby 3.3 Vcc
3. solder the 10nf capacitor between reset pin and ground

Here is a picture of one of my ethernet shields, with the reset "leg" bent outwards.

And this is the details of how I soldered the components on the back of the circuit.
In this position the components are nicely arranged on the back of the board.

With this mod, my arduino + ethernet shield is starting up correctly after powering up, and immediately works with no need of reset button push.

Marco ( @mgua )



braintagger said...

Cheers! Your mod works fine. Tested with a 10nF and 22nF on 2 shields (ran our to 10nF). Both seem to be working fine, the shield starts up and I get a ping 3s after connecting power.

Thanks a lot

macsolve said...

Didn't work for me. I didn't have 10nF so I used a 20nF (labeled 0.02µF). No link.
Uploads work though.

Anonymous said...

i wanted to test so soldered up the resistor to capacitor for reset lead and stuck the leads into top. but reset issue wasnt resolved. 10nf and 10k used. does it matter brand of ethernet shield? mine has sd card slot yours doesnt in example.

Tahir Mahmood said...

i think this is also a way to solve for this problum .....

Marco Guardigli said...

Thank you very much Tahir. Sorry for having published your comment with long delay. Hope the other users will find your comment interesting and useful.


Philippe H said...

Hello, thanks for the trick. It's working fine on a Mega2560 (but can't use the 5V of the card anymore - it freezes). Doesn't work for LEONARDO.
Thank you

The Bowen Family said...

Hi. I managed to have it stable using a 100nF cap, no resistor and the reset pin bent. However it only works when it is powered via the PC USB. If I use a regular 5V USB power supply I still have to reset it.

Does the CC3000 wifi shield with SD reader suffer the same problem?

Raffaele said...

Ciao Marco,
la mia 5100 ha iniziato a dare problemi. Non funziona più Tx/Rx ho provato anche con il reset ma nulla. Oggi proverò a saldare la resistenza e il condensatore.
La mia 5100 però ha l'sd a bordo.

Anonymous said...


I'm an engineer working at WIZnet provides W5100 to Arduino.
Arduino Ethernet shield does not designed with Power-On-Reset.
Your Idea is so good.

Can I introduce your some posts on WIZnet museum site(

Thanks in advance