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From: wte@ncrcae.Columbia.NCR.COM (Bill Eason)
Newsgroups: sci.electronics
Subject: Re: phone dialing (touch tone synthesis)
Message-ID: <3498@ncrcae.Columbia.NCR.COM>
Date: 22 Jun 88 20:22:46 GMT
References: <361@tiger.oxy.edu> <3310002@wdl1.UUCP> <4937@watcgl.waterloo.edu>
Reply-To: wte@ncrcae.Columbia.NCR.COM (Bill Eason)
Distribution: na
Organization: NCR Corp., Engineering & Manufacturing - Columbia, SC
Lines: 34

In article <4937@watcgl.waterloo.edu> awpaeth@watcgl.waterloo.edu (Alan Wm Paeth) writes:
>Original touch tone phones had *ONE* transistor -- there is nothing
>prohibiting an oscillator's generating two simultaneous frequencies...

How?

>As a second example, consider that a consumer phone line (one twisted pair)
>allows simultaneous (full duplex) conversation, yet each speaker hears his
>own voice in the headset at a much lower volume than the remote sender, all
>this done without the benefit of digital, let alone solid state components.
>Moreover, each phone contains no power supply -- the two leads to the exchange
>supply power, bidirectional data and also allow for remote ringing, yet each
>set contains only a handful of 1950's parts [but no vacuum tubes :-)].
>I don't think most folks could draw the circuit off the tops of their heads.

Can you?  Not to be sarcastic, just curious about how it's done.  How hard
would it be to make the support electronics (power supply, etc.) for your
own private in-house telephone setup?  Disregard touch tone decoding and call
routing, I guess... just the duplex/ringing/volume stuff.

>     /Alan Paeth
>     Computer Graphics Laboratory
>     University of Waterloo

(I never can remember when my .signature is automatically included...)

Bill Eason   (803) 791-6419    ...!ucbvax!sdcsvax!ncr-sd!ncrcae!sauron!wte
NCR Corporation		  ...!rutgers!mcnc!ece-csc!ncrcae!sauron!wte
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-- 

Bill Eason   (803) 791-6419    ...!ucbvax!sdcsvax!ncr-sd!ncrcae!sauron!wte
NCR Corporation		  ...!rutgers!mcnc!ece-csc!ncrcae!sauron!wte
E & M Columbia   3325 Platt Springs Rd.   West Columbia, SC  29169