Is It Possible to Build an Active Tag that Works with the RFID Card Reader?

NGO911

Hi,

I’m working on a school project and was wondering if it was possible to build an active RFID tag that will work with the Parallax RFID Card Reader module.

The concept for my project is as follows:
- A wireless lock system that allows users to open a door lock without ever having to take out the tag
- The reader will be attached on the door
- A tag within around 2ft of the reader will enable a motion sensor mounted on the door
- If motion is detected, the lock will unlock

As you can see, a passive tag will not work for this application since it needs to be within 4 inches and the user will still need to take the tag out of their pocket to open the lock.
If I designed an active tag (longer range) that transmits the correct sequence of bytes (ie. Start byte, 10 digit identifier bytes, stop byte), will the reader be able to correctly decode the bytes and output it to the serial pin?

Any help is appreciated.

SRLM

If you correctly emulated the passive tag, then you could certainly use an active tag. However, the passive tag doesn't just send out a radio signal, it feedbacks on the signal that the reader is sending out. So, I think it would be a good PhD project...

NGO911

Thank you for the response, SRLM.

The next question then is what are the characteristics of the signal that the reader gets from the tag? (ie. how is the unique ID modulated onto the 125kHz carrier and how does the reader demodulate the unique ID)

If I know the type of signal that the reader is expecting, then I can begin to attempt a transmitter design.

Mike Green

You need to do some research. The internet (and the Wikipedia) is your friend.

Here's one article: code.google.com/p/rfid-reader/wiki/HardwareDesign

That article references another that you can find using Google: ww1.microchip.com/downloads/en/devicedoc/51115F.pdf

Post Edited (Mike Green) : 10/1/2009 1:43:21 PM GMT

SRLM

If you make it through all 210 pages of the second document, then we'll know you are serious...

Another good reference is the book RFID Applications, Security and Privacy edited by Simson Garfinkel and Beth Rosenberg. It's from all the way back in 2006, but it is a good introduction to various aspects of RFID. You could always skip over the privacy and security sections, but I found the discussions on how RFID could potentially facilitate big brother fascinating

NGO911

Thank you for the links Mike Green!

The last thing I need to know before I begin the active tag design is what kind of modulation (ASK or PSK or FSK) and encoding scheme (NRZ, Manchester etc..) does the Parallax RFID Card Reader use specifically.

Is there anyway I can get this information?

Mike Green

I believe there's only one technique used with 125KHz passive tags and that's described in the documents whose links I provided.

NGO911

Thank you very much! I will use those documents as a reference and hope for the best.