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 ----- Original Message ----- From: "Brendan Moran" To: Sent: Wednesday, July 31, 2002 7:07 PM Subject: [EE]: RF cards: how do they work? > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > 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 > > -----BEGIN PGP SIGNATURE----- > Version: PGPfreeware 6.5.8 for non-commercial use > > iQA/AwUBPUh7xwVk8xtQuK+BEQKTxgCgnJDrdkT0B7rHh3MCOROfnhHGzFEAoI6Q > pD+/6eghJWji5+70AJr9K+0Z > =UyYO > -----END PGP SIGNATURE----- > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics