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Path: utzoo!utgpu!utcsri!asm
From: asm@utcsri.UUCP
Newsgroups: sci.electronics
Subject: Re: DTMF
Message-ID: <5166@utcsri.UUCP>
Date: Wed, 29-Jul-87 23:56:47 EDT
Article-I.D.: utcsri.5166
Posted: Wed Jul 29 23:56:47 1987
Date-Received: Sat, 1-Aug-87 00:37:30 EDT
References: <1377@mit-amt.MEDIA.MIT.EDU> <17966@cmcl2.NYU.EDU> <1319@genrad.UUCP> <1867@kitty.UUCP>
Reply-To: asm@utcsri.UUCP (Anees Munshi)
Organization: CSRI, University of Toronto
Lines: 26
Keywords: dtmf remote control
Summary: 

In article <1867@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:
>In article <1319@genrad.UUCP>, rep@genrad.UUCP (Pete Peterson) writes:
>> Unless you have a pile of op amps and R's and C's which are burning a hole in
>> your junk box (or other parts storage facility) and you are extremely
>> poverty stricken and take great delight in building and tuning multiple
>> bandpass filters, the integrated DTMF encoders/decoders are definitely the way
>> to go.
>
>	Right on!  Besides, most of the integrated receivers have far
>superior selectivity (read spurious signal rejection) than any receivers
>built with discrete tone detectors.  Not only can integrated receivers
>implement more filter poles than is convenient for discrete construction,
>but some of the newer integrated receivers use switched-capacitor filters.

	You can get a DTMF receiver for less than it will take to put
one together using op-amps etc. Just about everyone makes a dozen
chips to do this these days.

	For the fun of hacking though, nothing beats putting the stuff together
from scratch. It can be done using two bandpass filters and two phase-locked
loops (better than doing 8 filters!)

		anees munshi