Author Options:

How to wire 2 two-way switches in series to make a 2-way switch system!? Answered

Hey all, my teacher posed this question as extra credit and I've asked quite a few people and no one can figure it out.  The problem is: Use two 2-way switches to create a two-way-switch-system.  When I say 2-way swithces  I mean a switch with two copper screws.  Logically, it can't be done as both switches would need to be on for the circuit to work (power the bulb, that is) but a two way switch system means that either switch should be able to turn on the bulb.  This can easily be solved using two 3-way switches (one black screw and 2 copper screws) but this problem can only be solved using two 2-way switches, power, and the bulb.  I've drawn a bunch of schematics and I've gotten the closes to answering it.  So far, the closest thing I've had is to wire the switches in series but the circuit in parallel.  The answer to this is something so ludicrous that you just wouldn't do it, but there IS in fact a solution.  Please help! Email me at some114@gmail.com (please include pictures if you are able to! I'm uploading a link to a site with all my schematics.

link doesn't quite work yet; I'll have it up by 12:30 pm pacific time.



Please post the answers...even i need to know it...

Your wording is very obtuse.

By two-way switch, do you mean an spst switch?

You say nothing about whether the switches must be capable of independently switching the power on,


whether indeed that power, once applied by either switch can be interrupted by independent use of either switch.

That is, by strictly applying the crudely formed criteria you set, it would be as simple as mechanically linking the two toggles.

Which would make this another use of guile to imply intelligence, rather than an example of intelligence itself...

 Actually, I do, in fact, state that each switch needs to turn the bulb on separately.  And I know nothing about switches.  I don't know what an spst switch is.  That's why I described a two way switch as a switch with two copper screws.  If you go to home depot, it's the cheapest switch you can buy - it only has two terminals.

Actually, you don't. Your wording is either purposefully obtuse or  you shouldn't get extra credit for solving it by using others to do your work. Extra credit is for those who can solve problems ON THEIR OWN.

 Whoa there.  Calm down buddy.  This extra credit problem was assigned to us and I'll quote the teacher here, "You may use any resources you have to answer this question".  Therefor, it is actually perfectly acceptable for me to use this forum to try and get this answer solved.  And I have already thanked everyone (including you) for the answers I have received.

And actually, I did clearly state that both switches need to be able to turn the light on and off.  I said this using the simple statement "The problem is: Use 2 two-way switches to create a two-way switch system."  A two way switch system means that both switches should be capable of turning on or off the bulb.  Think about a hallway.  You start at one end and turn the light on.  Go to the other end and flip another switch.  The same light goes off. 

But do forgive me.  I really want to solve this extra credit problem (as the teacher said no one has solved it in years).  So, I was really anxious when I wrote this question.  But by the way, the definition of extra credit is: "extra credit is an addition, not necessarily a point for point addition, to the numerator of your score, but not it's denominator."  I'm pretty sure that doesn't say "extra credit must be solved by yourself to receive credit" (unless of course the teacher says you must solve it by yourself).  The professor who assigns the extra credit gets to set the standards for how he or she would like to give you extra credit.  Fortunately, for this situation, I'm allowed to use my resources, like instructables.com/answers. 

I would also like to point out that I am a freshman at a university.  Currently studying law... I have no idea how to solve this on my own.  And that's why I'm grateful for a community, like this, of people like you, and everyone else on this page, who are willing to answer questions like mine.  So again, I would like to thank you and everyone else.

Have you tried Google. Your link is not up yet but take a > Look < and see if this is what your looking for.

.  What the author of that page is calling 2-way switches, were called 3-way switches when I was in school here in the US. I assume they still are. :)

 No,  Three way switches have two copper screws and 1 black screw.  A two way switch has two copper screws and thats it. My teacher (a man with a PHD in both electrical and mechanical engineering) told us this - so I'm definitely going to trust this guy  lol.  He did say that everyone calls them the wrong thing - three way switches, but it's determined by the poles...or something like that, I forgot.  He said the simple way is to count the number of screws (terminals) on the switch.  2 screws means 2 way switch.

.  Maybe I am confused about what the author was saying. "Three-way" is a synonym for "single-pole, double-throw" (SPDT). If unspecified (eg, "hand me a toggle switch" or "hand me a wall switch"), SPST is assumed.

 I want to apologize for the late responses.  I set instructables to email me as soon as I got a new answer for this question.  However, I never received an email till this morning saying I had 15 new answers!  Thank you all!

I know exactly how to do it, but its non-obvious, and I don't know if you are allowed other components. My solution does use "only 2 way switches" though....


Your at washington.edu and you're asking around the internet for answers?


 I knew that would come up.  I'm a freshman with an undecided major asking people who, in my opinion, are pretty dang intelligent.  I'm also asking in a place where I can ask the question once and get many responses.  But, I'm also a freshman who has currently been studying computer science, not electricity. :P

If the switches have to be wired in SERIES then it can't be done.

Wired that way BOTH switches have to be on for the light to light.

But either can turn it off.

If the switches have to be wired in SERIES then it can't be done.

Oh yes it can.


 HAHA we've already determined that it IS possible.  We just don't know how.  And Steve is correct.

If ludicrous is what you want, is shorting past the bulb accepted?

Doesn't pass the test he sets. The switch shorting the bulb can't be bypassed. by the other, so you can't turn on the light, or convesely you can't turn it off with the first switch.

There is at least one solution though.


It fulfils the test as written,
a two way switch system means that either switch should be able to turn on the bulb.

If you have two switches in series shorting the power supply, opening either of them in isolation will remove the short and so turn on the bulb, but if one switch is open there is nothing the other switch can do to turn off the bulb.

All the convoluted arrangements I can find of two SPST switches either amount to AND or OR, though, and a full control system like you have with two SPDT switches is logically an XOR which I can't figure out how to achieve.

I'd like to see the full statement of the question: are extra bits allowed.

 Extra bits include as much wire and as many bulbs as you want.  BUT, you only get the 2 two-way-switches and a power suppy.

 This would be great, but unfortunately both switches would need to turn off the bulb.  If one switch was on, the other would need to turn it off.  

Well alright, extend it then, to my case, where you can do the whole on/off thing,

I suppose another solution might be to build your own relays from the ground up...

On a point of order, if two wires cross directly there is NO join between them, so you don't put a bridge in.