Article View: sci.electronics
Article #21807Re: Wanted: Phone-in-use Indicator
From: Harri Olavi Suomalainen
Date: Mon, 18 Dec 1989 10:15
Date: Mon, 18 Dec 1989 10:15
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In sci.electronics neumann@udel.edu (Brian R. Neumann) writes:
>
>Does anyone know of any simple circuit I could build or of any device
>that I could by to show when the phone is in use?
Voltage on the line is ~60 volts when line is free and ~10 volts while
the line is on use. You could bild up a simple device with only a few
transistors, fets etc. Notice that while the phone is ringing there is
~120VAC on the line! Be sure your circuit can take that!
Notice that you'll need an external power supply (eg. a battery) to
power your led. In case you'd take that "much" current from the line
your central office would find your line to be in use as if you'd
picked up a phone!
Chears, Harri Suomalainen
--
If you're feeling good, don't worry: you'll get over it !
c37189h@saha.hut.fi haba@otax.tky.hut.fi
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<1989Dec18.101522.20175@santra.uucp>Path:
arc1-ca.pugleaf.net!utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!samsung!think!mintaka!bloom-beacon!eru!luth!sunic!tut!santra!saha.hut.fi!c37189hReferences:
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Path: arc1-ca.pugleaf.net!utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!samsung!think!mintaka!bloom-beacon!eru!luth!sunic!tut!santra!saha.hut.fi!c37189h From: c37189h@saha.hut.fi (Harri Olavi Suomalainen) Newsgroups: sci.electronics Subject: Re: Wanted: Phone-in-use Indicator Message-ID: <1989Dec18.101522.20175@santra.uucp> Date: 18 Dec 89 10:15:22 GMT References: <6375@nigel.udel.EDU> Sender: news@santra.uucp (Cnews - USENET news system) Reply-To: c37189h@saha.hut.fi (Harri Olavi Suomalainen) Organization: Helsinki University of Technology, Finland Lines: 20