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From: wolfgang@haddock.UUCP
Newsgroups: sci.electronics
Subject: Re: I need a telephone ring detector chip
Message-ID: <441@haddock.UUCP>
Date: Tue, 21-Apr-87 23:39:26 EST
Article-I.D.: haddock.441
Posted: Tue Apr 21 23:39:26 1987
Date-Received: Thu, 23-Apr-87 23:46:17 EST
References: <228@phoenix.PRINCETON.EDU> <7940@utzoo.UUCP>
Reply-To: wolfgang@haddock.ISC.COM.UUCP (Wolfgang Rupprecht)
Organization: Home for Wayward Programmers
Lines: 22

>You have two wires coming in from the phone line.  First, each goes through
>a 100k resistor.  Then there is a 10M resistor between them.  Then one of
>them goes through a 0.02 uF capacitor, which should be rated for something
>like 200V.  Then there are two diodes in parallel between the lines, with
>opposite polarities (one with anode to top line, the other with cathode
>to top line):  one a 1N4148 and one the input LED of a 6N139 opto-isolator.

One minor point: The 10 meg 'bleeder' resistor could cause problems.
Some telephone line integrity tests involve measuring minute leakage
currants. Leakages in that range (<100 meg) are usually indicative of
brittle insulation on the line pairs. This could cause some repair
folks to investigate the source. (I'm not sure why the apps note
engineer felt he needed a bleeder. The capacitor has 200k in series
with it, and is only charged to 50 volts max. Not what you'd ever call
a shock hazard.)

Back (long before divestiture) when MaBelle still cracked down hard on
extra ringers on the line, I built an opto isolator out of an ne-2
(neon) bulb, series capacitor and resistor. I used a photo-darlington
for the detector. Talk about low load on the phone line.
-- 
Wolfgang Rupprecht 			haddock.ISC.COM!wolfgang