How to emulate FDX-B cat tag (hex)

125 kHz RFID
#1

Hello everyone
I have a shy cat and need to register that cat to the pet-door.
As I cannot get hold of that cat, I cannot read it’s rfid tag and copy it to the cat door.
From the veterinary, I got the 15-digit id-number of the fdx-b tag. but the flipper wats it in hex.
Anyone has an idea how to convert that 15-digit id-number to the 22-digit hex?

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#2

Good question, unfortunately I’ve paused my research at this topic. See: Animal tag “Bayer Animal Coder” issue - #10 by LupusE

I would search the source code of flipper as next step, for a better understanding.

#3

I don’t see the pattern. None of the Hex seems to match my tag when I convert it to decimal. I did notice that editing the first part of the hex gave me errors. Editing the end didn’t seem to change the number on mine. Sadly I’ve been very busy without much time to tinker.

#4

Here is, how the Flipper will decode FDX-B: flipperzero-firmware/protocol_fdx_b.c at dev · flipperdevices/flipperzero-firmware · GitHub

I’ve already read of the manchester encoding, but I am not familiar with this.

The 15 digits should already contain the Country Code. Sometimes the Number is just a string of digits, sometimes there is a dash, f.ex. 276-098nnnnnnn96. The first part is the country code
And than there is some CRC and parity calculation.

Interesting is the Comment at line 109 to 142.
I was not aware that T: is for the temperature.

The flipper shows a Hex Value above in the screen, I have not found this printf() so far, but I am reading on my phone screen in the highway. I will wait until home, to go through in a IDE.

Edit: Typo

#5

That’s interesting. I may have to find one with a temperature sensor to play with.

#6

I am afraid this is
a. a placeholder for future use
b. for another application

Since the RFID tag got its energy from the readers antenna, I can’t imagine it is enough to power an active sensor.

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#7

I don’t know how much energy a temperature sensor uses so you may be right. There’s a smart padlock powered by NFC but I suspect NFC can inject more power then 125kHz RFID. On the padlock they harvest the energy into a capacitor that can actuate the lock.

EDIT: Found one that claims to have temperature. I don’t think there is much utility in it but I’m really just interested in the technology.

#8

As far as I see now, the first 12 digits of the hex code are that animal identification number. and the first number in hex is somehow the last in dec.
The last 10 hex digits are always the same on those chips I’ve seen so far: 00 01 00 00 10.
There inside you have the “Animal: yes” and probably also the temperature (then, the 00 probably change)

I’m still trying to figure out, how they code the ID into that hex.
The “-” or the space after the country code is just to help reading. I haven’t seen it in the code yet.

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#9

That was the last 10 digits of mine until I change it to 00 01 00 00 30. I saw no difference in the tags details after changing them though.