Article View: sci.electronics
Article #11567Re: Phone line monitor
From: Brian Rossmajer
Date: Wed, 11 Nov 1992 00:53
Date: Wed, 11 Nov 1992 00:53
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In article <1992Nov10.135145.6174@bnr.ca> mwandel@bnr.ca (Markus Wandel)
asks for a phone line monitor. I`ve been comtemplating this myself
for a while now. Couldn`t you just hook up an op-amp with the - input
to the phone ground and battery ground and the tip to the + input of
the op-amp. Then power an LED off the output of the amp. With a pot,
If you want to minimize loading, put some precision resistors (say 1 Mohm)
in a voltage divider across the phone line, and your op-amp goes between
ground and tip div 2.
This should be safe and easy, but I haven`t built it and I haven`t done
the calculations. Has anyone tried it or know immediately why it wouldn`t
work?
--
bwrossmajer@descartes.uwaterloo.ca (Brian W. Rossmajer)
BrI University of Waterloo; Computer Science, Electrical Engineering
Disclaimer: What is truth? Is mine the same as yours?
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Newsgroups: sci.electronics Path: arc1-ca.pugleaf.net!sparky!uunet!utcsri!torn!watserv2.uwaterloo.ca!watmath!undergrad.math.waterloo.edu!cantor.math.uwaterloo.ca!bwrossma From: bwrossma@cantor.math.uwaterloo.ca (Brian Rossmajer) Subject: Re: Phone line monitor Message-ID: <BxJ15D.6vK@undergrad.math.waterloo.edu> Sender: news@undergrad.math.waterloo.edu Organization: University of Waterloo References: <BxGK30.K71@mtholyoke.edu> <27344@oasys.dt.navy.mil> <1992Nov10.135145.6174@bnr.ca> Date: Wed, 11 Nov 1992 00:53:36 GMT Lines: 16