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From: zielke@eniac.seas.upenn.edu (Stephen Zielke)
Newsgroups: sci.electronics
Subject: Need DTMF Decoder/Ringing Detector
Keywords: Need IC's to detect ringing and decode DTMF touch tone signals.
Message-ID: <5317@super.upenn.edu>
Date: 7 Jul 88 15:24:56 GMT
Sender: news@super.upenn.edu
Reply-To: zielke@eniac.seas.upenn.edu (Stephen Zielke)
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Organization: University of Pennsylvania
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I am doing a mini-project for an electronics class and I need a little
help.  

I will be building a gadget that will be connected to a phone jack and
when it is called it will answer the phone after a pre-set number of rings.
After it answers the phone an audio tone will be sent to indicate that it
is ready to accept touch-tone commands.  The caller can then enter touch-
tone commands and a microcontroller will act on these commands.

1. I need a ringing detector.  The Texas Inst. TCM1520A will output a
   TTL level signal during the presence of the AC ringing signal.  This
   would be used to detect/count the number of rings.  Anyone ever use
   this IC or know of a substitute?
2. Answering the phone would be done by closing/opening a relay.  Should
   be no problem here.
3. Sending the audio tone to the caller should not be much of a problem
   either.
4. Dectecting the DTMF touch tone signals is the main problem.  There are
   plenty of DTMF encoders that are used in the telephone (accepting
   signals from a keypad).  But the DTMF DECODER, which would be present
   in the central office, seems to be more difficult to find.  Anyone know
   where to get one of these chips?

Thanks in advance,

	Steve Zielke

		zielke@eniac.seas.upenn.edu         
		..!rutgers!eniac.seas.upenn.edu!zielke