I followed a simple tutorial on setting up an RGB LED. The LED uses pins 11, 12 and 13. Via the serial interface I can issue commands such as the following:


The letters activate the color, and the number immediately after the letter specifies the brightness of the color.

That worked just fine. I then decided to find a way of controling my RGB project from a web interface. To make the connection to the internet, I mounted my Ethernet shield on my Arduino Uno, included a MAC and server IP address etc.

In my setup function, when I call ethernet.begin(), I get very strange combined effects.

  • The red aspect of my LED is permanently on
  • My sketch no longer responds to my input

Can anyone offer any ideas why a call to ethernet.begin() would have such negative effects, please ?

  • 6
    \$\begingroup\$ I don't know anything about arduinos, but quite possibly the ethernet hardware you added assumes it can use the pins you have your LEDs connected to. This is one of many examples why just blindly plugging in pieces of hardware and software from others leads to trouble without the proper level of understanding. \$\endgroup\$ – Olin Lathrop Nov 11 '12 at 13:45

As Olin said, the Arduino talks to the Ethernet shield using those pins - the SPI bus. See here. Try using different pins for the LEDs.

  • \$\begingroup\$ ethernet shield uses 10,11,12 & 13 number of pins and that is the reason it gives you a negative response \$\endgroup\$ – user46205 Jun 24 '14 at 14:17

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