RFID Detector

pabloko SP · Guest

Hi friends,

Firstly sorry for my english, I'm Spanish.

I'm building a rfid TAGS detectors, this tags works at 13.58MHz but my tags works at 8.2MHz

I need generate 8.2MHz by PWM, and show the voltage result, when is near a tag the voltage drops, I have to setup comparator.

Any idea ?

Thanks

MarcosAmbrose · Joined: 25 Sep 2006 Posts: 38 Location: Adelaide, Australia

Hi pabloko SP,
It would be easier to find a tag reader that is compatible with your cards then interface your microcontroller to the tag reader.

FvM · Joined: 27 Aug 2008 Posts: 2337 Location: Germany

Generating the drive voltage for a RFID reader is a very simple problem compared to processing the received signal. It depends of course on your definition of operation volume and coupler geometry. But generally, you can expect that usual RFID readers are operating noise-limted at their maximum receiving distance, e. g. 10 cm for a ISO 14443 card with a not too large sized antenna respectivly coupler. This implies rather sophisticated receiver technology than simply detecting a voltage drop.

For a restricted operation distance, the receiver electronics can be actually simpler. At the driver side, most reader ICs have simply a digital square wave output, that is converted to a bandwidth-limited sine waveform by RLC filters, that also perform the coupler impedance matching. You should study datasheets and application notes of usual reader ICs (e. g. from Philips) to learn the details.

As another point, a 8.2 MHz reader would need a very good suppression of harmonics to comply with regulations, although the permitted emissions at the fundamental are comparable with a 13.56 MHz reader, when I understand ETSI EN 302 291 correct.

P.S.: Apart from complying with legal regulations, it's no problem to operate a 13.56 MHz reader IC at a lower frequency.

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

Trying to generate 8.2MHz with a PIC PWM output is hopeless. You need dedicated hardware to go that fast. It is better to choose a PIC crystal speed that is 8.2MHz, or use a multiple with a divider. Then use a logic gate, or several in parallel as a driver, then a filter to your antenna.
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