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From: atn@cory.berkeley.edu (Alan Nishioka)
Newsgroups: comp.dcom.telecom
Subject: Should Projects be Connected to the Phone Line?
Message-ID: <74667@bu.edu.bu.edu>
Date: 13 Feb 91 05:33:15 GMT
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X-Telecom-Digest: Volume 11, Issue 114, Message 4 of 10


Thank you to all who answered my previous message about my project
causing the phone to stop ringing.  I responded via EMAIL.

However, in response to my article, John Higdon brought up a problem
that had been bothering me.  He said that my project SHOULD comply
with the various parts of the FCC rules since it needed to connect
directly to the phone network.

Now, many books and magazines regularly publish projects that connect
to the phone line.  Even the usually respectable TELECOM Digest
recently published several such projects.  I don't think any of them
have been certified anything by anyone.

I see two issues involved: One of safety (to craftspersons, etc. ) and
the other of just following the rules.  I can see if I were going to
sell these devices that I would be interested in both, but as a
hobbyist I am mostly interested in the first.

I understand there are network interface devices that one can buy and
thus have any device automatically safe and certified to connect to a
line, but these are out of my budget.  I also don't see how they make
that much of a difference.

I plan to power my project using a 12VDC transformer unit since the
lights take more current than the line can provide.  I have a
1MEG/5MEG voltage divider across the line to read voltages and plan to
drop a 255ohm resistor across the line with a transistor for a hold
function.  All of this is prefaced by a bridge rectifier.

Is this safe?  Are there other concerns here that I am missing?
Should *anyone* build *anything* that connects to the phone line?  Can
it be reasonably priced?  Does the phone company really care?  Should
I do it anyway and just kinda feel guilty? :-)


Alan Nishioka      KC6KHV      atn@cory.berkeley.edu      ...!ucbvax!cory!atn
974 Tulare Avenue, Albany CA 94707-2540     37'52N/122'15W    +1 415 526 1818