Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!cyclops!csense!bote
From: bote@csense.UUCP (John Boteler)
Newsgroups: comp.dcom.modems
Subject: Re: Device to indicate phone line in use?
Message-ID: <249@csense.UUCP>
Date: 26 May 89 12:37:58 GMT
References: <298@indri.primate.wisc.edu>
Organization: Common Sense Computing, McLean Va
Lines: 30

From article <298@indri.primate.wisc.edu>, by bin@primate.wisc.edu (Brain in Neutral):
> Do devices exist that can be put on a phone line to indicate whether
> the line is already in use?  This would be used in a situation where
> two people in a home each have a modem, and one wants to know if the
> other is on, without picking up a phone to find out.  

There is a discussion in comp.dcom.telecom raging about this
now.

I came up with a different idea while reading your request, plus
this has been used in a similar configuration before.

Dig yourself up two relays, fairly small and cheap, which operate
on ~5-10 volts and pull in with about 5-10 ma of current; you
can find these at Radio Shack for maybe $5 US.

Connect each relay's coil in series with the tip of each phone line.

Connect each relay's normally closed contacts such that they 
interrupt the other line when the first phone is off-hook and
drawing current through the relay.

Now you won't possibly be able to use the other phone when 
the first is in use, and vice versa. Automatic exclusion key!


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