Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!cica!tut.cis.ohio-state.edu!ucbvax!ucdavis!csusac!mmsac!jim
From: jim@mmsac.UUCP (Jim Lips Earl)
Newsgroups: sci.electronics
Subject: Re: Wanted: Phone-in-use Indicator
Summary: Here's the schemo!
Message-ID: <2895@mmsac.UUCP>
Date: 22 Dec 89 00:41:28 GMT
References: <6375@nigel.udel.EDU>
Lines: 43

In article <6375@nigel.udel.EDU>, neumann@udel.edu (Brian R. Neumann) writes:
> 
> Does anyone know of any simple circuit I could build or of any device
> that I could by to show when the phone is in use?  A small LED would 
> be helpful --  I'm getting tired of the family picking up the phone while 
> I'm using the line for the computer.  I haven't seen anything like this 
> available.  It sounds simple to me, but that doesn't necessarily mean
> it is.  
> --

I got a lot of mail requesting this schematic.  So here it is, best I could do,
ascii-wise.  This is from Popular Electronics, Dec.89 issue, by TERRANCE KELLY.
It's called THE EXTENSION SILENCER.  Here is what it does:  you place the
following circuit in series with EACH telephone that is hooked to your incoming
phone line.  All phones will ring normally, and the first one to answer locks
out the others.  Someone picking up an extension will hear nothing if the
line is already in use.  If you need to switch extensions all you have to do
is pick up one extension and hang up the other.
 
phone   -  <--------------------------------------------------------> red
line    +  <----|
                |             1-amp, 50-PIV triac                       to
                |                                                       phone
                |                     | /|                              -----
                |                MT1  |/ | MT2
                |_____________________|\ |__________________________> green
                |                    /| \|              |
                |                 G / | /|              |
                |                  /  |/ |              |
                |                 |            15v zener|
                |                 |          \ 1N4744   |
                |       1k        |          | /|       |       
                |------/\/\/------|----------|< |-------|
                                             | \|
                                              \
 
If you have trouble making the thing work, try swapping the +/- leads coming
into the circuit from the phone line.
-- 
      Jim "Lips" Earl             UUCP: ucbvax!ucdavis!csusac!mmsac!jim
          KB6KCP              INTERNET: mmsac!jim@csusac.csus.edu
   =======================================================================
                  The opinions stated herein are all mine.