I read that the status LED on the Duemilanove Arduino Board is connected to the DigitalPIN 13. If I connect a LED to it, it blinks with a simple program like this:
digitalWrite (13, LOW);
However, if I connect the NFC Shield to the Arduino board, and connect the LED on the same pins (13 and GND), the Shield does not work anymore.
Using the code on this page (seeedstudio.com/wiki/NFC_Shield), I get “Didn’t find PN53x board”.
Why does the board fail to work when a LED is connected to PIN 13? The Shield is detected when the LED is disconnected.