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Article #14864Re: Phone taps/other extensions up
From: Angelo Campanella
Date: Sun, 13 Dec 1992 08:05
Date: Sun, 13 Dec 1992 08:05
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The best way to detect another phone being "off-hook" is to measure the DC voltage across the line. When no one is using the line, it is about -48vdc. When one phone is off hook, it is about -10vdc (don't hold me to an exact figure). When the second phone goes off hook, that voltage drops to aboy 6vdc, etc. I leave it as "an exercise for the student" to build a display circuit for this phneomenon. As you can see, you can start with a VOM!
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<1992Dec13.080519.20438@magnus.acs.ohio-state.edu>Path:
arc1-ca.pugleaf.net!sparky!uunet!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu!acampaneReferences:
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Newsgroups: sci.electronics Path: arc1-ca.pugleaf.net!sparky!uunet!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu!acampane From: acampane@magnus.acs.ohio-state.edu (Angelo Campanella) Subject: Re: Phone taps/other extensions up Message-ID: <1992Dec13.080519.20438@magnus.acs.ohio-state.edu> Sender: news@magnus.acs.ohio-state.edu Nntp-Posting-Host: top.magnus.acs.ohio-state.edu Organization: The Ohio State University References: <1992Dec8.230105.2028@sol.cs.wmich.edu> Date: Sun, 13 Dec 1992 08:05:19 GMT Lines: 8