Path: utzoo!mnetor!uunet!husc6!think!ames!ucbcad!ucbvax!JASPER.PALLADIAN.COM!dp
From: dp@JASPER.PALLADIAN.COM (Jeffrey Del Papa)
Newsgroups: comp.dcom.telecom
Subject: Temporarily out of service
Message-ID: <871203231158.1.DP@BANFF.PALLADIAN.COM>
Date: 4 Dec 87 04:11:00 GMT
References: 
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: Jeffrey Del Papa 
Organization: The ARPA Internet
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Approved: telecom@xx.lcs.mit.edu


    Date:         Tue, 24 Nov 87 09:02:34 EST
    From:         Phil Bowman 


    Does anyone out there know how to put a switch on a residential telco line
    (the red and green wire) to simulate a busy condition to incoming callers
    and to suppress the ring of the phone itself?  Is there a way to add a
    neon light to show the line is off-hook (I think there are 90 volts on the
    line)?


ring prevention is fairly easy - a pair of diacs in series across the pair will
block ringing (a diac is a bistable 4 layer diode, below the threshold (40 volts
typically) it is an open circut, above it, a short.)
 All subscriber loops have protective devices on them that shut down a voltage
source if a short is detected. thus ring (90v) is put on the loop, the diacs
conduct on the first half cycle, and the ring is removed from the loop. this
doesn't count as call completion, so the other party will often hear ringing
continue. diacs used to be available at rat shack, they may still be.