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Article #21166Re: Sensing telephone off-hook
From: Andy Tefft
Date: Sun, 16 Apr 1989 17:06
Date: Sun, 16 Apr 1989 17:06
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A while ago a friend of mine mad a simple circuit with a couple of transistors that would light a green led when the phone was on-hook and red when off-hook. There's a fairly LARGE voltage difference (around 30 volts or so i think) between off-hook and on-hook, which should be quite easy to detect. If you engineer the thing right you can run it off the phone company's power. I just made a voltage divider and stuck an led in there, set up so that the on-hook voltage would light the led ok, but the off-hook voltage was too small for any light.
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arc1-ca.pugleaf.net!utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!psuvax1!psuvm.bitnet!art100References:
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Path: arc1-ca.pugleaf.net!utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!psuvax1!psuvm.bitnet!art100 From: ART100@PSUVM.BITNET (Andy Tefft) Newsgroups: sci.electronics Subject: Re: Sensing telephone off-hook Message-ID: <81719ART100@PSUVM> Date: 16 Apr 89 17:06:18 GMT References: <22901@agate.BERKELEY.EDU> <21000013@m.cs.uiuc.edu> Organization: Penn State University Lines: 9