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From: drewes@cory.Berkeley.EDU (Rich Drewes)
Newsgroups: sci.electronics
Subject: Phone Electronics Questions
Message-ID: <23934@pasteur.Berkeley.EDU>
Date: 12 Apr 90 05:07:42 GMT
Sender: news@pasteur.Berkeley.EDU
Reply-To: drewes@cory.Berkeley.EDU (Rich Drewes)
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Organization: University of California, Berkeley
Lines: 22

hi hi hi,

I have a few telephone electronics questions maybe you can help me with.
I want to sit on the phone line and look for DTMF (dual tone multi-frequency)
signals.  My current circuit works by using a low impedance (8 ohm)
audio 8:1000 transformer in series with the tip line.  The ring line
remains untouched.  My circuit looks at the high impedance side of the
transformer to read the signal.

Question 1:  Is my transformer component choice a good one?

Question 2:  Is there is solid state component that would perform
the tapping and isolation function that the transformer now performs?

Question 3:  What precautions should I take on my circuit side regarding
the high voltage ringing signal passing through the transformer?  Are
diode shunts enough protection?

Thanks for your help.

Rich
drewes@cory.berkeley.edu