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Path: utzoo!utgpu!water!watmath!clyde!rutgers!husc6!uwvax!astroatc!nicmad!kunert
From: kunert@nicmad.UUCP
Newsgroups: sci.electronics
Subject: Re: Library Book detectors
Message-ID: <1640@nicmad.UUCP>
Date: Mon, 27-Apr-87 14:22:08 EDT
Article-I.D.: nicmad.1640
Posted: Mon Apr 27 14:22:08 1987
Date-Received: Wed, 29-Apr-87 01:21:54 EDT
References: <146@illusion.UUCP> <868@oliveb.UUCP> <1726@kitty.UUCP>
Organization: Nicolet Instrument Corp., Madison, WI
Lines: 20
Summary: my best guess

In article <1726@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes:
> 	Now, THINK, people!  How does this system work???  It's really
> rather clever!  If no one guesses the correct answer, I'll post it in a
> week.
> 

I worked in a library that used a similar system, but there was no way
to deactivate the sensor. The "tag" inserted in the book was just a
printed loop connected to a printed capacitor forming a resonant circuit-
the system was designed so that the library employee would pass the books
around the sensor at the checkout.

Anyway, in the systems that *can* be deactivated, I believe the mechanism
used at the checkout is a simple magnetizer/demagnetizer. My best guess
is that a reed switch is being used to short out the tuned circuit.

-- 
                      ihnp4-\                  "I'm looking for a lifestyle
Dick Kunert      seismo!uwvax!nicmad!kunert     that doesn't require my
                     decvax-/                   presence..."