"Hacking" an NFC Tag

[jsxgt]

Hey everyone,

A while back, I bought a cheap barebone NFC tag from here.

The tag works pretty well using my phone, I can read it, and write to it, and everything else an NFC tag is supposed to do. What I would like to do though is to see if I can use this with an Arduino. I know there are all sorts of shields and NFC readers, but I was actually thinking of something more direct. That's the "hack" part of my idea.

This NFC tag has the contacts on the chip exposed. I'm think it should be relatively easy to solder another pair of wires to it, and have the Arduino interact with the tag directly. Why would this be useful, since the main point of NFC is that it's wireless. you ask? Well, I'm thinking of turning this chip into a very cheap dynamic NFC tag. So basically, write data to it via the wired connection to the Arduino, then touch the chip with a phone to read the data. Maybe even have it work the other way around, and have a phone app that writes some data to the chip and have Arduino read it and act on it.

So basically my question is, is it possible to have Arduino power and interact with the NFC chip directly, without using any reader? If so, any idea where I could find some documentation regarding talking to this chip in this manner?

I'm sorry if this has already been mentioned someplace else, but I have not found it. Sorry also if this is not the proper section for this question.


Thanks a lot!

[Boardburner2]

The interface to the tag is rf using a type of phase shift modulation at 13 mHz or so.

Id say it would be impossible to get an arduino to do that without hardware.
Also have to supply tag power using 13 MHz.

[Grumpy_Mike]

This NFC tag has the contacts on the chip exposed.

Can you see a diode and capacitor on the input to the chip?
If you can remove them then you might be able to inject an arduino signal straight in. However you will then not be able to read it with your phone so I suppose it doesn't get you very far.

[jsxgt]

It only has the coil which is connected directly to the chip.

I was thinking it may work similarly to OneWire, which if true should be doable, if you know the protocol to talk to it.

But not sure how similar it is to the proper NFC protocol, considering it's doing the powering and reading directly.

[Grumpy_Mike]

I was thinking it may work similarly to OneWire, which if true should be doable

Sadly it is nothing like the OneWire.

from:-
http://en.wikipedia.org/wiki/Contactless_smart_card

The standard for contactless smart card communications is ISO/IEC 14443. It defines two types of contactless cards ("A" and "B")[6] and allows for communications at distances up to 10 cm (3.9 in)[citation needed]. There had been proposals for ISO/IEC 14443 types C, D, E, F and G that have been rejected by the International Organization for Standardization. An alternative standard for contactless smart cards is ISO/IEC 15693, which allows communications at distances up to 50 cm (1.6 ft).

To start your hunt
http://en.wikipedia.org/wiki/ISO/IEC_14443
But you might have to end up paying for a copy of the spec.

Basically the 13MHz signal is used to supply power and the chip transmits back at about 3.5MHz.