Decoding the pulse dialing should be easy enough. If you consider what the
mechanism was 40 years ago, i.e. the mechanical central office, with
stepping relays which responded to the pulses created by your telephone, it
will become obvious that what each number did was drive a stepping relay
which selected which bank of relays would be the destination of the next
stream of pulses. If you count the pulses, which wil be at either 10 or 20
Hz, depending on the age of the telephone generating them, you'll get the
number dialed. count/time the pulses. When one pulse is missing or 10 have
been accumulated, go to the next digit ...
Certain digits have special meanings, i.e. starting with a '1' meant it
should expect a 10-digit number instead of a 7-digit one. A '0' also had
special meaning, didn't it?
If you poke around in some of the older National Semiconductor data books,
there are plenty of circuits which they no longer sell which show details of
how many of these functions are created, including the DTMF decoding, etc.
EXAR and Signetics published lots of examples also. It's no coincidence
that they all sold PLL components.
Dick
-----Original Message-----
From: Arfon Gryffydd <arfonrg_at_texas.net>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Wednesday, December 01, 1999 9:07 AM
Subject: Re: Teleco Question... More on my devious plan....
>First, Thanks to all who have helped so far...
>
>
>I have some old modems (TRS-80, acoustic and etc.) which I would like to
>use (flashing LEDs are cool) so, I want to build a little telco emulator to
>interface with the modems in one of my Linux boxes.
>
>I figure an LM556 for the dial tone... A tone decoder for dialing... Not
>sure an easy way to decode pulse dialing.
>
>As for ring... I am thinking using two charged capacitors and switching
>them. That's the first method I came up with to limit the current cheaply.
>
>Any suggestions? I'd like to do this for less that $25.00.
>----------------------------------------
> Tired of Micro$oft???
>
> Move up to a REAL OS...
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Received on Wed Dec 01 1999 - 10:52:01 GMT