albert@ucbarpa.Berkeley.EDU.UUCP (03/25/87)
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). Can the same design be used to let 3 or more switches turn a light on or off? Anthony Albert ..!ucbvax!ucbarpa!albert albert@ucbarpa.Berkeley.EDU
albert@ucbarpa.Berkeley.EDU.UUCP (03/26/87)
Well, I thought about it some more and figured it out. It requires 2 DPDT
switches.
___
____ \___ _ _ _ _ _ _ _ _ _ __| \___
| |
_________| |________
|_____ |
\___ _ _ _ _ _ _ _ _ _ ____ \___|
This represents 2 DPDT switches connected by 2 wires (_ _ _). To create a
similar circuit with 3 switches, they'd have to be 4 pole. In general, a
n-1
circuit with n switches requires each to have 2 poles.
Anthony Albert
..!ucbvax!ucbarpa!albert
albert@ucbarpa.Berkeley.EDUroy@phri.UUCP (03/26/87)
In <18002@ucbvax.BERKELEY.EDU> albert@ucbarpa (Anthony Albert) asks
about 2 or more switches controlling a light, and/or a phone. The 2
switches controlling a light work like this:
*------------------*
/ \
Hot -------* A B *------------}
} <--- this is supposed
*------------------* +---} to be a light bulb
|
Neutral ---------------------------------------+
I've drawn switches A and B such that the lamp is on. If you
reverse either A or B, the lamp goes off. If you reverse *both* A and B,
the lamp is on again, using the other conductor for the hot leg. If you
want to have more than 2 switches controlling a light, you put any number
of the following in between A and B:
----------* *------------ -----------*---*-----------
\ /
\ vs.
/ \
----------* *------------- -----------*---*------------
The artwork isn't very good, but imagine a switch with 4 contacts.
In one position, the contacts are cross connected as shown in the left
diagram, in the other position the contacts are connected straight through
as shown on the right. If you think about it the right way, each switch is
an exclusive-or gate. If Y = X1 xor X2 xor X3 ... xor XN, by changing the
state of an odd number of the X's, you change the state of Y. If you
change the state of an even number of X's, the state of Y remains the same.
If you want, you can think of the lamp as the parity check bit for the
switches.
This all works fine for electric lights because one side of the
line is hot and one side is neutral (or at least, it should be!). Phones
don't have a neutral side, so I don't know what would happen if you try it
with your telephone. Note: if you put the switches on the neutral (instead
of the hot) leg, it *will* work, but will violate all known electric codes
and be a serious safety hazard as well. If you don't know what you're
doing, get a qualified electrician to do it for you.
--
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016
"you can't spell deoxyribonucleic without unix!"woolstar@cit-vax.UUCP (03/26/87)
in article <18008@ucbvax.BERKELEY.EDU>, albert@ucbarpa.Berkeley.EDU (Anthony Albert) says: > > Well, I thought about it some more and figured it out. It requires 2 DPDT > switches. > In general, a > n-1 > circuit with n switches requires each to have 2 poles. A simpler method that I remember from my dad's electrician's handbook is: ____ ____ __ __ _____ / \ / \ / \ / \ o o o o o o o o o o o \ / \ / \ / (+) --o \/ \/ etc.. \/ o--- [light] -----(-) /\ /\ /\ / \ / \ / \ o o o o o o o o o o o \____/ \____/ \__ __/ \_____/ SPDT DPDT DPDT DPDT SPDT So it's just a matter of fliping any switch to close or disconnect the path. This should work for phones also. -- -------------- John D Woolverton "Yes it's true..." jdw@tybalt.caltech.edu woolstar@csvax.caltech.edu
woolstar@cit-vax.UUCP (03/26/87)
> A simpler method that I remember from my dad's electrician's handbook is: > > ____ ____ __ __ _____ > / \ / \ / \ / \ > o o o o o o o o o o o > \ / \ / \ / > (+) --o \/ \/ etc.. \/ o--- [light] -----(-) > /\ /\ /\ > / \ / \ / \ > o o o o o o o o o o o > \____/ \____/ \__ __/ \_____/ > > SPDT DPDT DPDT DPDT SPDT > Let me just clarify that for SPDT and DPDT o o--o o o o o-o | o o | | o o--o o o o o-o State 1 State 2 Sorry about anyone who didn't quite understand. -- -------------- John D Woolverton "Yes it's true..." jdw@tybalt.caltech.edu woolstar@csvax.caltech.edu
psfales@ihlpl.UUCP (03/26/87)
In article <18002@ucbvax.BERKELEY.EDU>, albert@ucbarpa.Berkeley.EDU (Anthony Albert) writes: > 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). This is quite simple once you see it, but it was a revelation to me when I first figured it out: Switch A Switch B -------------------- / ---------o o---------- Light ------- | / | 120VAC -------------------- | | | --------------------------------------------------------- A similar system should work for an extension telephone. -- Peter Fales UUCP: ...ihnp4!ihlpl!psfales work: (312) 979-7784 AT&T Information Systems, IW 1Z-243 1100 E. Warrenville Rd., IL 60566
awpaeth@watcgl.UUCP (03/26/87)
In article <18008@ucbvax.BERKELEY.EDU> albert@ucbarpa.Berkeley.EDU.UUCP (Anthony Albert) writes: >Well, I thought about it some more and figured it out. It requires 2 DPDT >switches. > > > ___ > ____ \___ _ _ _ _ _ _ _ _ _ __| \___ > | | >_________| |________ > |_____ | > \___ _ _ _ _ _ _ _ _ _ ____ \___| > > >This represents 2 DPDT switches connected by 2 wires (_ _ _). To create a >similar circuit with 3 switches, they'd have to be 4 pole. In general, a > n-1 >circuit with n switches requires each to have 2 poles. > > I missed the original question - but if it is a matter of turning a light on or off from any of N switches, then 2P2T switches suffice. The solution is a circuit which maintains circuit parity, using a "double rail" signalling convention (lamp current and "signal" are synonomous): -AC-----. <+ +--> .-----. <+ +--> . .--- load ------(ground) | . | . <etc> --.-- --.-- . | . | . <--+ +->.-----. <--+ +->. . Each switch is 2P2T wired in a polarity reversing arrangment (the throws oppose in the diagram, and move together). In one state, the two inputs pass through to the two outputs, in the other, they reverse roles. At any stage, the upper (lower) rail carries AC, while the lower (upper) rail is left floating. For an N switch circuit, the end switches need only be SPDT, as half the switch is unused. These are termed "three way" switches in hardware stores. The remaining N-2 intermediate switches need only provide four external connections. They are sold under the name "four way". Incidentally, MOS (as opposed to Bipolar) VLSI technology allows one to build analogous structures very easily. These have merit in doing parity operations (e.g. the Sum bit in a full adder is the parity of both addends and the carry in) using "switch" and not "gate" logic, which can often reduce circuit area and reduce propagation delay. /Alan Paeth
ted@blia.UUCP (03/26/87)
You can get n switches in the circuit without using bigger than double pole
switches. The end two switches are SPDT wired just as you figured out.
The rest of the switches are DPDT wired into the two wires running between
the end switches so that operating the middle switch cross connects the wires.
o------+
----------o +---------------
\ |
o--+ |
| |
o--+ |
| |
----------o +-------------------
\ |
o------+
This gives the desired result of any switch switching the circuit.
--
===============================================================================
Ted Marshall
Britton Lee, Inc.
p-mail: 14600 Winchester Blvd, Los Gatos, Ca 95030
voice: (408)378-7000
uucp: ...!ucbvax!mtxinu!blia!ted
ARPA: mtxinu!blia!ted@Berkeley.EDU
disclaimer: These opinions are my own and may not reflect those of my employer;
I leave them alone and they leave me alone.
fortune for today:
Things are more like they used to be than they are now.jmc@riccb.UUCP (03/27/87)
> 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
has@ukc.UUCP (03/28/87)
The easist way to do this is as follows: -------+ |------------------------------------------------------------------+ | | POWER | C D | | *------------* *------------* +-------+ | |----*=== ===*------| LIGHT |--+ -------+ *------------* *------------* +-------+ A B switch 1 switch 2 switch 3 Switch 2 is a double pole, double throw reversing switch. The contacts are arranged as follows: Contacts ( A-->B and C-->D ) or ( A-->D and C-->B ) Switching any switch will reverse the state of the light. This can be extended as far as is neccessary. HOWiE. Howard Shaw, Physics Lab., University of Kent, Canterbury. England. has!ukc
jel@psuvm.bitnet.UUCP (03/28/87)
In article <860@riccb.UUCP>, jmc@riccb.UUCP (Jeff McQuinn ) says: > 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. > > Jeff McQuinn just VAXing around Really?? I've never heard of a device that could start to ring with only one line going into it... Is there some sort of a ground involved? How would one ground a phone? All 7 of the phones in our apt aren't grounded. Wouldn't the phone company get upset if one did this (ground the phone)? And finally a question to the original poster: Why ARE you trying to do this?? - Jon Stolen from some comedian: "I work for the Bell System... Taco Bell." #! rnews 1270 Relay-Version: Version 1.0
pozar@hoptoad.UUCP (03/28/87)
I don't know if this is the answer to anyones question, I popped
in half way through. The way lights are switched with two switches:
_ ________________
/|
/__________/ ______ ( light bulb ) _____
\ / |
_______________ |/_ |
|
/___________________________________________________________|
\
This scheme requires two spdt switches and two wires between the
switches.
Tim
--
Tim Pozar
UUCP pozar@hoptoad.UUCP
Fido 125/406
USNail KLOK-FM
77 Maiden Lane
San Francisco CA 94108
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