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From: acm@bu-cs.BU.EDU (ACM)
Newsgroups: sci.electronics
Subject: How do you build phone off-hook indicator
Message-ID: <12660@bu-cs.BU.EDU>
Date: Tue, 8-Sep-87 13:14:44 EDT
Article-I.D.: bu-cs.12660
Posted: Tue Sep  8 13:14:44 1987
Date-Received: Wed, 9-Sep-87 05:35:46 EDT
References: <414@gtx.com> <4046@utai.UUCP>
Reply-To: madd@bucsb.bu.edu
Organization: ODO (Organization for the Disorganization of Organization)
Lines: 22

Ok you wizards out there.  I have 4 phones (on one line) in my suite
which are being used by 6 people.  Obviously there is some contention
for phone-time.  It's a pain to have to pick up the phone (and bother
someone) to see if someone is on the line.

Now, I know there is a voltage differential between on-hook and
off-hook (I believe it's 24 volts on-hook and 10 off-hook but this is
purely from memory and I could be wrong).  How can I build a simple
circuit to light an LED when the voltage drops?  I'd prefer the
simplest curcuit possible that's pretty reliable.

Thanx for any help.  Please email replies to madd@bucsb.bu.edu (or if
that doesn't work try acm@bu-cs.bu.edu or if that doesn't work just
post it although I don't read this group often, being a software
person).

jim frost
madd@bucsf.bu.edu
madd@bucsb.bu.edu

"But God favors drunks, small children, and the cataclysmically stoned...."
                                         -- Stephen King, _It_