Ethernet Shield interferes with I2C LCD Module

Hi all, I am currently struggling with my Arduino Setup(Arduino Uno R3 with w5100 Ethernet shield mounted). I use the Arduino to control WS2811 Led Strips via Artnet (Adafruit library with the excellent code from I recently bought an LCD and an I2C Module to output the IP-adress of the Art-Net Node. Everything works fine when I run the devices separately, e.g. the Artnet output works without the LCD connected and the LCD works without the Ethernet-shield being connected. The problem occurs when I connect the SCL and SDA-leads from the LCD to the Pins on the Ethernet-Shield. The Node just freezes(LEDs stop refreshing) and so does the Uno. What am i doing wrong? I checked the manual from the ethernet shield, and it does not seem to use the A4 & A5 pins or am I mistaken? Any help would be greatly appreciated :) Kind Regards, Maikel

Could you post a link or schematic of the LCD and I2C module?

The ethernet shield doesn't use A4 or A5, but maybe there is a different issue...

Thanks for the reply! The Display is a HD44780 1602 LCD Module (Link: The I2C-Module is a I2C Adapter Serial Interface Board (Link: I am wondering if the Uno does not have sufficient SRAM to handle the load. When I compile the code 57% of dynamic storage is being used... Any thoughts?

As a tip, next time posts the links as real links with the “links” button… i hate copy-pasting for other people…

And 57% isn’t bad… I run programs into the 95%'s and they run for ages…
Can you post your code perhaps? I’m getting the feeling where looking in the wrong direction. The 2 should work together… (Post your code by selecting the “</>” button please!)

Sorry about the links… I’m thought they would be transformed automatically, won’t happen again.
The code ist from and I added the Liquidcrystal-I2C-library from here:
Here’s my *.ino file

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>
#include <Artnet.h>
#include <Ethernet.h>
#include <EthernetUdp.h>
#include <SPI.h>
#include <Adafruit_NeoPixel.h>

// Neopixel settings
const int numLeds = 100; // change for your setup
const int numberOfChannels = numLeds * 3; // Total number of channels you want to receive (1 led = 3 channels)
const byte dataPin = 7;
Adafruit_NeoPixel leds = Adafruit_NeoPixel(numLeds, dataPin, NEO_RGB + NEO_KHZ800);

// Artnet settings
Artnet artnet;
const int startUniverse = 0; // CHANGE FOR YOUR SETUP most software this is 1, some software send out artnet first universe as 0.

// Check if we got all universes
const int maxUniverses = numberOfChannels / 512 + ((numberOfChannels % 512) ? 1 : 0);
bool universesReceived[maxUniverses];
bool sendFrame = 1;
int previousDataLength = 0;

// Change ip and mac address for your setup
byte ip[] = {192, 168, 2, 5};
byte mac[] = {0x04, 0xE9, 0xE5, 0x00, 0x66, 0xEC};
LiquidCrystal_I2C lcd(0x27,16,2);  // set the LCD address to 0x20 for a 16 chars and 2 line display
void setup()
  lcd.begin();                      // initialize the lcd 
  // Print a message to the LCD.
  artnet.begin(mac, ip);

  // this will be called for each packet received

void loop()
  // we call the read function inside the loop;

void onDmxFrame(uint16_t universe, uint16_t length, uint8_t sequence, uint8_t* data)
  sendFrame = 1;
  // set brightness of the whole strip 
  if (universe == 15)

  // Store which universe has got in
  if (universe < maxUniverses)
    universesReceived[universe] = 1;

  for (int i = 0 ; i < maxUniverses ; i++)
    if (universesReceived[i] == 0)
      sendFrame = 0;

  // read universe and put into the right part of the display buffer
  for (int i = 0; i < length / 3; i++)
    int led = i + (universe - startUniverse) * (previousDataLength / 3);
    if (led < numLeds)
      leds.setPixelColor(led, data[i * 3], data[i * 3 + 1], data[i * 3 + 2]);
  previousDataLength = length;     
  if (sendFrame)
    // Reset universeReceived to 0
    memset(universesReceived, 0, maxUniverses);

void initTest()
  for (int i = 0 ; i < numLeds ; i++)
    leds.setPixelColor(i, 127, 0, 0);;
  for (int i = 0 ; i < numLeds ; i++)
    leds.setPixelColor(i, 0, 127, 0);;
  for (int i = 0 ; i < numLeds ; i++)
    leds.setPixelColor(i, 0, 0, 127);;
  for (int i = 0 ; i < numLeds ; i++)
    leds.setPixelColor(i, 0, 0, 0);;

So i ordered an Arduino Mega to check if it was due to the lack of ressources. Unfortunately the problem still persists.. Any ideas? Kind Regards, Maikel

Hallo, I have the same probleme, Have you solved in some way?