Simple circuit to find lost passport

[Jasen Betts]

Hello all,

My passport is somewhere inside my apartment but for the life of I can't
remember where. I have looked at all the obvious places and I could not
find it.
Now, this is a new "biometric" passport with the RFID chip inside.
So I'm looking for a simple and most of all cheap circuit that could
activate the RFID chip and so tell where (roughly) that little bugger is
hiding.

the detection range will be a few centimetres.

Do you know of anything that could do this?
Maybe something that plugs to a PC under windows or linux?

I have had a look at dedicated RFID readers but on top of being very
expensive, they seem to have a reading range of only a few centimeters
which is a bit too little for the kind of search I'm looking at.

It should be possible to get a longer range, but cost goes up
dramatically for long range readers.


OTOH you might have success using a dip meter tuned to the resonant
frequency of the RFID tag (13.56Mhz), Perhaps equipped with a loop
antenna instead of the usual compact coil. I don't have a dip meter
so I can't test it on a generic RFID tag here.

 

[Jasen Betts]

The devices that are inserted into pets obtain their energy from the
varying magnetic field generated by the reader, and return their signal
by modulating the power being absorbed.

For a device that is only intended to be read from a short distance,
that technology seems the obvious to use, and it would be difficult to
read the device from a greater distance.

I can imagine a device that aborbs energy at one frequency, and
transmits a signal on a different frequency. It would be easier to power
and read such a device from a distance, but why bother making it that way?

It just happens. passports use "IEC 14443" which operates at 13.56MHz

AIUI if the the card is using load modulation it shorts the antenna
reflecting some half-cycles, in effect transmitting on a subharmonic

www.waazaa.org/download/fcd-14443-2.pdf
(a more up-to-date(?) version can also be purchaed from IEC)