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'[EE]: RF cards: how do they work?'
2002\07\31@204154 by Brendan Moran

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Someone asked me recently about this wierd card. He showed me the
card, and all it appeared to be was a white minimally translucent
piece of plastic (with a bit of a spongy core), about 2mm thick.  He
just was wondering how it worked, and now I'm wondering too.  He says
that he can just wave it in front of the sensor and it reads the
card, by which I assume that it is an RF based technology.  It takes
no batteries, and is sealed all the way around.

Anyone know this technology?

- --Brendan

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2002\07\31@221415 by M. Adam Davis

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RFID.  It is essentially a largish coil, a capacitor, and a tiny
microcontroller (more or less).

The reader sends a signal at a frequency that the coil resonates at, the
capacitor (and other components) store the energy, and power the micro,
which replies with a string of data, optionally.

Microchip sells RFID chips, you can start looking at their literature
for an overview (and fine view) of the technology.

-Adam

Brendan Moran wrote:

{Quote hidden}

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2002\07\31@230347 by Herbert Graf

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> Someone asked me recently about this wierd card. He showed me the
> card, and all it appeared to be was a white minimally translucent
> piece of plastic (with a bit of a spongy core), about 2mm thick.  He
> just was wondering how it worked, and now I'm wondering too.  He says
> that he can just wave it in front of the sensor and it reads the
> card, by which I assume that it is an RF based technology.  It takes
> no batteries, and is sealed all the way around.
>
> Anyone know this technology?

       Look up RFID, it's pretty common these days. The company I work for
recently coverted from swipe cards to this type of card, makes it much
easier to get it around (since you just have to bring the card close to the
reader instead of swiping it). Plus the cards last longer. TTYL

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'[EE]: RF cards: how do they work?'
2002\08\01@091111 by Jim
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A technology that has been around for at least 10
years (early 90's) that I can testify too - these
were used for secure access at a telecom carrier's
HQ building I worked at in '93.

I classify these as "coupled magnetic field" devices
as opposed to *true* RFID products (although the sales
dweebs will call them "RFID Products").

RFID products will work at distances of feet to many feet
(like the cards affixed to windshields that work to provide
automatic pay on the tollway systems around here) whereas
these cards won't work (ours didn't anyway) much more than
3 inches away form "the card reader".

Also - when TDMA RF technology cellular phones came into use
in our system we began encounter problems when entering the
parking garage (the garage required "card" access) if engaged
in an active callphone call ... these digital TDMA phones
interfered with either the "readers" or the cards to the
point that one had to end a call in order to get the card
"to read".

As to methodology - I can see where tuned circuits in the
frequency range of 100 KHz or so could be easily used to
couple to the card and the resulting 100 KHz energy rectified
to power a PIC or other low-power processor-based ID system.

RF Jim

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