[solved] funduino mini Wiznet W5100 Ethernet module (red), power supply issues

I have a couple of these modules and I’m trying to use them with Arduino Unos and Megas.

I’m very confused because the adverts specify a 3.3v power supply but the board clearly shows a V+5 input and it has an AMS1117 3.3v LDO regulator on board.

This wiki and other posts on this forum suggest the board should run from a +5v power supply but it doesn’t work with any of the basic Arduino Ethernet example sketches when I use +5v.

When I run it from a 3.3v power supply it DOES work. When I supply the V+5 pin on the W5100 Ethernet module with 3.3v the on board AMS1117 is only outputing 2.4v to power the W5100 chip.

Here’s a link to a schematic of the W5100 module which seems to correspond to the ones I have.

When I power the module with 3.3v it draws about 170mA so I can’t use the 3.3v output on the Arduino. I have to provide a separate power supply. The project I am working on is tight for space so I would much prefer to use the +5v output on the arduino, as other members of this forum seem able to.

I can’t find any reference to this issue on this forum or google. I would very much appreciate it if any of the members could confirm if they have experienced this issue or if they have any suggestions what may be causing it or any solutions for fixing it.

The connections from the W5100 module to the Arduino (Uno) are to pins 10(SS), 11(MOSI), 12(MISO), 13(SCK).

Use 5v power. It does have an onboard regulator.

Connect to Uno (Mega)
V+5 to 5v,
MO to D11 (D51)
MI to D12 (D50)
SCK to D13 (D52)

Thanks for your reply confirming it should work on 5v power.

I went back and tried again and for the first time one of the modules did work on 5v but it was unreliable on power up or reset. If I power it up or reset it 4 or 5 times I can get it working again.

My connections are as you specified but include SS on the module to D10 on the Arduino.

I’m aware there are some issues with resetting the W5100 module and I’ve seen some posts on the forum relating to this and will go back and check them now.

I think the reason I was getting the confusing results detailed in my original post is that the W5100 module will run on 3.3v power even after the AMS1117 drops it to 2.4v and in that configuration it does seem to work reliably on power up or reset.

In my original tests it always worked on 3.3v but not on 5v power. I was lucky when I tried it again on 5v, after your reply, that it did work first time. But subsequent tests confirm that it is unreliable. I have verified this on 3 modules and 2 arduinos.

I am testing it by pinging the module and the arduino is running this sketch:

#include <Ethernet.h>
byte mac_addr = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xEE };
IPAddress ip(192, 168, 1, 175);

void setup() {
delay(250); // wait in case Arduino comes out of reset before W5100
Ethernet.begin(mac_addr, ip);

void loop() {

I’ll go and look further into the reset issue.

I think my problems relating to this issue were caused by too many jumper wires on my breadboard prototype. I tidied up the wiring and following the advice from Albmik in this thread Arduino Mega 2560 and W5100 (non-shield) - Networking, Protocols, and Devices - Arduino Forum I put a grounded aluminium foil shield around the SPI bus wires. The W5100 module then worked reliably on 5v. I then found that it still works without the foil shield so the excessive number of jumper wires I was using may have been the problem. Perhaps this relates to the speed of the SPI bus (I've only used I2C in the past). Anyway, it all now works reliably so that's great.