Path: utzoo!utgpu!cunews!spock!grayt
From: grayt@spock (Tom Gray)
Newsgroups: sci.electronics
Subject: Re: Ring signal generation (was DTMF Decoder IC)
Keywords: resonance
Message-ID: <4838@smithd>
Date: 12 Oct 90 15:17:29 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> <1990Oct10.151422.6001@zoo.toronto.edu> <2876@jaytee.East.Sun.COM>
Reply-To: grayt@smithd (Tom Gray)
Distribution: na
Organization: Mitel. Kanata (Ontario). Canada.
Lines: 25

In article <2876@jaytee.East.Sun.COM> gsteckel@east.sun.com (Geoff Steckel - Sun BOS Software) writes:
>It's fairly easy (:-) to generate quasi-sort-of-sine-looking-things at
>more-or-less 60-80VAC 20HZ by taking a filament transformer (remember them?)

In this discussion, one must remeber that the object of the ringing signal
is to alert the user. When he is alerted he will take the telephone off hook
and the telephone system (in this case the KSU) must detect this transition.

The 20Hz ringing signal must be a very clean sine wave for this to happen 
releiably. Any imperfections in the sine wave will make the task more
difficult. If not done correctly the dreadded result of PRE-TRIP will
happen. In this case, the system will see transiensts from the ringing
signal and falsely decide that the telephone is off hook.

Remembet that the ringing generator is driving up to 5 telephones with
a variety of ringing devices from electronic to mechanical. The impedance
of this configuration can range from 50K to 1.2K or 800 ohms. The ringing
detector and ringing generator must operate reliably into all of these
loads.

Although telephone ringing sounds trivial - it is not a trivial task to
make it operate reliably - with all types of telephones into all types
of loops.