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From: gtisqr!toddi@beaver.cs.washington.edu (Todd Inch)
Newsgroups: comp.dcom.telecom
Subject: Building a Phone Line Simulator
Message-ID: <15079@accuvax.nwu.edu>
Date: 28 Nov 90 21:10:19 GMT
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X-Telecom-Digest: Volume 10, Issue 854, Message 5 of 10


Someone (oops, lost the article) requested a phone-line simulator with
some special needs which amounted to one side dropping current when
the other side went on-hook.  Ringing wasn't a requirement.

Here's my favorite, assuming you don't need dialing to do anything in
particular, don't need ringing of any sort, and don't need dial tone.
(Yes, that limits its application a bit!)

   To phone, speakerphone, fax, other device

               |     |
               |     |
    9 Volt  -------  |
    Battery   ---    |
               |     |
               |     |

   To other phone, speakerphone, fax, etc.

This works for everything I've ever tried.  I've heard it'll even work
for a couple of "dumb" FAX machines that don't listen for dial tone.
If your speakerphones need lots of voltage, you might put a few 9 Volt
batteries in series to increase voltage as necessary.  On some
(especially older) touch-tone equipment, the polarity has to be
correct, so just reverse the wires if it goes "clunk" instead of
"beep" when you press the buttons.  (Not that the tones will actually
DO anything with this circuit.)

Turn those old phones you've got laying around into "field sets" for
the kids to play with.  Sorry, no ringing.

Todd Inch, System Manager, Global Technology, Mukilteo WA  (206) 742-9111
UUCP: {smart-host}!gtisqr!toddi    ARPA: gtisqr!toddi@beaver.cs.washington.edu