Path: 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

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.