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- Newsgroups: sci.electronics
- Path: 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
-
- 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?
-