Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!eplunix!raoul
From: raoul@eplunix.UUCP (Nico Garcia)
Newsgroups: sci.electronics
Subject: Drawing DC phone current
Keywords: SK2086, phones
Message-ID: <1084@eplunix.UUCP>
Date: 28 May 91 15:54:30 GMT
References: <1081@eplunix.UUCP> <8053@nst>
Organization: Eaton-Peabody Lab, Boston, MA
Lines: 20

In article <8053@nst>, grayt@Software.Mitel.COM (Tom Gray) writes:
> Draw less than 4mA from the loop and you will not have any 
> problems.

Only works in the off-hook position, Tom. A standard phone is about 600
ohms, and has about 10 Volts across it off-hook. That's *about* 15-20 mA:
the standards are deliberately extremely broad. It's not clear at all to me
that 4 mA will not maintain the "off-hook" status in the phone company's
circuits. However, the phone company does *not* want DC paths available for
the on-hook state. 

In fact, let me go try this (putting a 2700 ohm resistor across my office
phone line). Hmmm: goes off-hook as the voltage drops to 18 volts. Maybe my
line is picky, but forcing it off-hook is not what *I* want from an
in-use detector.

-- 
			Nico Garcia
			Designs by Geniuses for use by Idiots
			eplunix!cirl!raoul@eddie.mit.edu