Seeedstudio NFC Shield Problems

Edit to original post:

Apparently, if I use any of the pins on the NFC shield, for example to light an LED, the Arduino cannot detect the NFC shield. I’m using essentially the same code as on the Seeedstudio wiki page ( . The shield works fine if nothing else is plugged in to its pins, but if I plug in the led, the shield cannot execute its nfc.getFirmwareVersion() method.

I am trying to figure out why I cannot use the I2C communication between one Arduino and another with the NFC shield (see post below)… and this could be why.

Any thoughts why this would be happening?

Hi folks. I’m trying to connect two Aruduino Unos via IC2. On one of the Arduino Unos, I have the Seeed Studio NFC shield, and I want to send a scanned card’s number to another Arduino with an Ethernet shield.

Everything works until I connect the NFC shield to one of the Arduinos. That is, Arduino+Ethernet shield communicates just fine with another Arduino. But Arduino+Ethernet does not communicate with Aruduino+NFC. I am connecting the wires to the same pin locations on the NFC shield as I did when it was just the Arduino. But no information is being sent to the master.

Any ideas what could be going on? The NFC shield works when it’s just being used as a reader, but it just seems like the IC2 pins aren’t the same as on the Arduino Uno.

Any suggestions would be extremely helpful, so thanks for any advice.


Hi, i tried to plug in LED as you said, the NFC Shield can be detected by Arduino.
And on the NFC Shield, the I2C and SPI pins are multiplexed, so if you connect two Arduinos via I2C, it maybe disabled.

Thanks for the reply. If the I2C and SPI pins are multiplexed on the RFID shield, then how do you suggest I transmit information from the RFID reader to another arduino connect to an ethernet shield?

Also, how did you determine that the I2C and SPI pins are multiplexed?