Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Using "Free" telephone power
Summary: Self-powered modems are older than one may believe...
Message-ID: <3139@kitty.UUCP>
Date: 3 May 89 04:43:15 GMT
References: <636@serene.UUCP> <920@snjsn1.SJ.ATE.SLB.COM>
Organization: Recognition Research Corp., Clarence, NY
Lines: 34

In article <920@snjsn1.SJ.ATE.SLB.COM>, greg@bilbo (Greg Wageman) writes:
> >Can anybody offer insite on the secrets of running audio amps and chips off
> >the meagre phone line power?  How 'bout the ammount of current the phone line
> >can source?
> 
> I've used line-powered modems.  They use all CMOS parts to keep
> current consumption down, and as I said, since an off-hook device is
> required to draw a certain amount of current, why not use it to power
> the modem?

	Interestingly enough, the Western Electric 113-type data set in
its "plain vanilla" form was totally telephone-line powered.  This is
a 300 baud originate-only modem which was developed around 1970.  It
used NO IC's whatsoever, and employed discrete germanium and silicon
transistors.  I always thought it was a pretty clever design, but also
sort of silly to go to all that trouble for a box twice the size of
a 500-type telephone set that was ALWAYS used where AC line power was
available.  Musta been someone's pet project at Bell Labs... :-)

> Even if you could, you would have to
> cope with the possibility of an incoming ring signal, which is
> typically 60-90 VAC!  (Yes, Virginia, you can ring a phone with house
> current.)

	Sorry, but you canNOT ring a phone with "house current".  Virtually
all conventional telephone ringers are frequency selective, and operate only
between 16 and 32 Hz; 60 Hz won't cut it.  Some ringers used on older
party line systems (like the "harmonic", "decimonic" and "synchronic") were
_very_ freqeuncy selective, with a "bandpass" of 5 Hz or less.

<>  Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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