Article View: sci.electronics
Article #21309Re: Using "Free" telephone power
From: John Opalko, N7KBT
Date: Wed, 03 May 1989 19:25
Date: Wed, 03 May 1989 19:25
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In article <2829@skivs.UUCP>, dr@skivs.UUCP (David Robins) writes: > > I don't know how it is now, but the old Princess and other Bell System > phones had dials with incandescent bulbs, whcih were powered off AC by > a small wall transformer. The newer phones use an electroluminescent panel that is, indeed, powered by the CO battery. What I'm trying to figure out is how you folks who hang voltage dividers and LEDs across your phone pairs keep from frying things when the ~100 VAC ringing current arrives. I imagine you can get a big, honking capacitor that has a low reactance at 20 Hz and shunt it around the LED, but... :-) John Opalko uunet!nwnexus!thebes!mcgp1!jgo PS: How much do 8,000 mfd non-polarized caps cost, anyway? :-)
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arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!uw-june!uw-entropy!dataio!pilchuck!ssc!mcgp1!jgoReferences:
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!uw-june!uw-entropy!dataio!pilchuck!ssc!mcgp1!jgo From: jgo@mcgp1.UUCP (John Opalko, N7KBT) Newsgroups: sci.electronics Subject: Re: Using "Free" telephone power Message-ID: <1879@mcgp1.UUCP> Date: 3 May 89 19:25:34 GMT References: <636@serene.UUCP> <2829@skivs.UUCP> Organization: McCaw Cellular Communications, Inc., Seattle, WA Lines: 24