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From: ee251aaz@sdcc3.UUCP
Newsgroups: sci.electronics
Subject: Re: Library Book detectors
Message-ID: <3875@sdcc3.ucsd.EDU>
Date: Wed, 22-Apr-87 00:51:55 EST
Article-I.D.: sdcc3.3875
Posted: Wed Apr 22 00:51:55 1987
Date-Received: Fri, 24-Apr-87 00:01:13 EST
References: <959@obelix.UUCP> <1104@nonvon.UUCP> <5941@pur-ee.UUCP> <2835@mit-hermes.AI.MIT.EDU> <17024@sun.uucp>
Reply-To: ee251aaz@sdcc3.ucsd.edu.UUCP (Gregory Breit)
Organization: University of California, San Diego
Lines: 23
Summary: Maybe it's not an LC circuit...

In article <17024@sun.uucp> cmcmanis@sun.uucp (Chuck McManis) writes:
>In article <2835@mit-hermes.AI.MIT.EDU>, jpexg@mit-hermes.AI.MIT.EDU (John Purbrick) writes:
>> My girlfriend visited a library at MIT with me a while ago, and she was
>> carrying a book (legally obtained) from a different college's library.
>> As we left through the stolen-book detector, the beeper went off... 
>
>It occured to me reading this that the 'deactivation' may be nothing more
>than charging up the capacitor in the LC circuit...
>
>comments?

This is a nice idea, but I could swear that I have repeatedly
entered and exited similarly equipped libraries here carrying books
I checked out weeks prior.  The capacitive circuit would need to
possess an incredibly long time constant for this to be possible.  It
would seem somewhat impractical to design a security system that
did not allow you to re-enter (or exit thereafter) the library with
a book you checked out some time before.  I hope there is someone
out there who knows the answer....

Gregory Breit
Department of Applied Mechanics and Engineering Science
University of California, San Diego