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From: jmc@riccb.UUCP
Newsgroups: sci.electronics
Subject: Re: Question about multi-switched lights
Message-ID: <860@riccb.UUCP>
Date: Fri, 27-Mar-87 06:46:33 EST
Article-I.D.: riccb.860
Posted: Fri Mar 27 06:46:33 1987
Date-Received: Sat, 28-Mar-87 13:49:47 EST
References: <1922@ihlpl.ATT.COM> <562@puff.WISC.EDU> <3972@fritz.UUCP> <18002@ucbvax.BERKELEY.EDU>
Organization: Rockwell Telecommunications, Downers Grove, IL
Lines: 36
Summary: Answer

> I want to put switches on a phone line so that an extension phone in the
> basement can be turned on and off at its location in the basement and also
> upstairs. I realized that this is the same type of circuit which is used
> to turn on stairway lights from the top and bottom of the stairs.  This must
> be a fairly simple circuit, but I can't figure out how it's done (without
> taking it apart anyway).
> 


                             S1-a            S2-b
        Tip >----------------o/ o------------o--o--------------> Tip to Phone
                     |                                  |
                     |       S1-b            S2-a       |
                     --------o--o------------o/ o--------


       Ring >--------------------------------------------------> Ring to Phone

                      S1-a = Normally open contact of a 2PST switch
                      S1-b = Normally closed contact of S1

                      S2-a = Normally open contact of a 2PST switch
                      S2-b = Normally closed contact of S2

                  (These are the ON-ON type of switches with 3 terminals)

               This scheme allows the phone to ring but cannot close the loop
               to answer.  If you don't want it to ring either, simply put the
               switches on the Ring lead instead of the Tip lead.

> Can the same design be used to let 3 or more switches turn a light on or off?
> 

          No.  At least I can't think of how it could be done.  

                                          Jeff McQuinn just VAXing around