Path: utzoo!attcan!uunet!samsung!uakari.primate.wisc.edu!dali.cs.montana.edu!milton!wiml
From: wiml@milton.u.washington.edu (William Lewis)
Newsgroups: sci.electronics
Subject: Re: How Do I Make a Phone In-Use Light?
Message-ID: <4633@milton.u.washington.edu>
Date: 2 Jul 90 02:25:53 GMT
References: <5349@mmsac.UUCP> <1558@yenta.alb.nm.us> <904@eplunix.UUCP>
Organization: University of Washington, Seattle
Lines: 37
Distriburion: usa

In article <904@eplunix.UUCP> raoul@eplunix.UUCP (Nico Garcia) writes:
>In article <1558@yenta.alb.nm.us>, dt@yenta.alb.nm.us (David B. Thomas) writes:
>> Another neat phone circuit (VERY simple) uses an scr, a couple of resistors
>> and a button.  If you wish to switch phones, you hold in the button (gating
>> the scr), then hang up.  The scr maintains loop current.  An led could be
>
>Ummm, can you post this one? Enough of us do occasional phone hacking that
>I'd like one as well.


    I second that. It would be extremely useful around here ...

   Anyway, re: tying phone lines together to make a DIY conference
calling set-up: So far, I haven't tried it with three lines (it would
require stringing more wire, rather than just hooking up the unused pair
in the 4-conductor cable already in place), but it works great with 
two lines, well enough that someone on the other end of one line can
touch-tone dial the other line after I throw the switch. As it is, 
I'm just shorting the lines together (being careful about
polarity =8) ). The off-hook voltage goes up a little when both
lines are going into one phone (from 5+ volts to 7 or 8), but it
seems to have no adverse effects upon the system. I do feel a little
uncomfortable just shorting the lines, so as soon as I get a pair
of capacitors of a reasonable value I'm going to put them in.
   I tried it first with a pair of capacitors I use for power-supply
bypassing on digital circuits (0.1 uF? the numbers on the side are
104) and the signal was pretty faint but understandable. (I didn't
have any more reasonable values lying around =8) ) I'll keep the
net informed if the circuit does anything interesting.


    


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