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From: roy@phri.nyu.edu (Roy Smith)
Newsgroups: sci.electronics
Subject: Re: Ring signal generation (was DTMF Decoder IC)
Message-ID: <1990Oct11.013436.6335@phri.nyu.edu>
Date: 11 Oct 90 01:34:36 GMT
References: <14793@mentor.cc.purdue.edu> <27114b84-483.1sci.electronics-1@vpnet.chi.il.us> <14913@mentor.cc.purdue.edu> <9770@uhccux.uhcc.Hawaii.Edu>
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Organization: Public Health Research Institute, New York City
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> the correct ringing signal on a spec FCC telephone set (ha ha ha, find
> one) is 90 VRMS @ 20 hz.

	How about the following to generate a fairly ugly 90 VRMS @ 20 Hz
signal?  First, step 115 VRMS @ 60 Hz (i.e. mains power) down to 90V, and
full wave rectify it.  Generate a 60 Hz TTL square wave train by any one of
a number of methods involving some combination of zener diodes, and schmidt
trigger comparators.  Run this into a divide-by-3 (2 flip-flops, plus a
couple of gates).  Use the 20 Hz TTL output of the divide-by-3 to drive a
solid-state DPDT relay (basically 4 big CMOS analog switches), cross
connected to reverse the polarity of the 90 VRMS, 60 Hz full wave rectified
waveform generated in step 1.  The output should look like:


      *     *     *                       *     *     *
    *   * *   * *   *                   *   * *   * *   *
   *     *     *     *                 *     *     *     *
---*-----*-----*-----*-----*-----*-----*-----*-----*-----*-----*-----*----*---
                     *     *     *     *                 *     *     *    *
                      *   * *   * *   *                   *   * *   * *   *
                        *     *     *                       *     *     *

	As an alternative, you could use the 1940's technology,
brute-force, electro-mechanical way.  Use the 115V 60 Hz mains to drive an
N-pole synchronous motor.  Couple the shaft to a 3N-pole 90V synchronous
generator (maybe even on the same shaft in the same case) and out comes
your 90 VRMS 20 Hz ringing signal, probably with an efficiency approaching
90%.  Why do I have the feeling that if I go down to the centrex room in
our building, I might actually find something like this?
--
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
roy@alanine.phri.nyu.edu -OR- {att,cmcl2,rutgers,hombre}!phri!roy
"Arcane?  Did you say arcane?  It wouldn't be Unix if it wasn't arcane!"