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I have two sets of lights in my bedroom. There are also two light switches. One double light switch is by one door, and turns both sets of lights on or off (one switch does one set, one does the other).

There is also another light switch near the bed - this is a single light switch. It turns on and off one of the sets of lights regardless of how the double switches are set. I gather that this is either a 2-way (UK, where I am) or a 3-way (US) lighting system.

I am going to be replacing the double switch near the door with some relays so that I can control them over the internet. I don't really use the other switch, and I want to do away with it for simplicity's sake. There are pictures of the light switch and a rather crude diagram of what it looks like from the back attached. Which one of those wires is dispensable?

Bonus points if anyone can provide a schematic for this kind of set-up. I'd like to know how it works.

Back of switch from the side Top view Crude Diagram of the back of the switch

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    \$\begingroup\$ Should be migrated to diy.stackexchange.com \$\endgroup\$ – Spehro Pefhany Sep 15 '16 at 18:09
  • \$\begingroup\$ @SpehroPefhany happy to migrate this - how do I go about doing that? \$\endgroup\$ – Archie Roques Sep 15 '16 at 18:25
  • \$\begingroup\$ I believe a moderator has to do it, and I don't see the option to recommend migration specifically to DIY in the flagging so I just added a comment. I think it's a well laid-out question, just not ideal for this site. \$\endgroup\$ – Spehro Pefhany Sep 15 '16 at 18:30
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You would require something along these lines where SW1 is the switch by your bed:

schematic

simulate this circuit – Schematic created using CircuitLab

The research that you would need to do is: can you drive relays with the GPIO of a microcontroller (I think probably not).

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  • \$\begingroup\$ You can definitely drive relays from a MCU: see link as an example. There are lots of MCU-specific relay boards available for cheap online -I'm planning to use one of those and likely an ESP8266. In your example, does it require SW1 to be in that position? I am happy to totally abolish SW1, make a connection and replace it with a blanking plate, in fact I'd rather do that for simplicity. \$\endgroup\$ – Archie Roques Sep 15 '16 at 21:17
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I don't understand why you want to get rid of the light switch and replace with relays but I can offer clarification of how your switches work:

schematic

simulate this circuit – Schematic created using CircuitLab

The SPDT switches on the left of the diagram that I have drawn make up the six terminals that you have on the light switch by your door and the third is the switch by your bed.

If you could explain what you are hoping to achieve I may be able to help further.

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  • \$\begingroup\$ Thanks - that helps me understand what I'm dealing with! I'm doing an IoT project and hoping to control them from the internet (Phillips Hue is expensive!!). Question edited accordingly. \$\endgroup\$ – Archie Roques Sep 15 '16 at 20:21
  • \$\begingroup\$ This is very interesting as I did a project a few months ago very similar to this where I designed a smartphone application and controlled some lights using a Bluetooth interface and a microcontroller. \$\endgroup\$ – Chris Johnson Sep 15 '16 at 20:26
  • \$\begingroup\$ I fear that this project may be slightly more involved than you first expected and you may to go away and do some researc on the subject as it is not a simple case of just removing the light switch and replacing with relays. \$\endgroup\$ – Chris Johnson Sep 15 '16 at 20:27
  • \$\begingroup\$ Is it not possible to just cut out the extra switch from the operation entirely and replace the two light switches with 2 relays? Alternatively I could fit one relay above each light fitting, as they're quite easy to get to and modify. Harder though, and annoying because I think they're all in series and it's gonna get messy. Also I'd have to have four microcontrollers. \$\endgroup\$ – Archie Roques Sep 15 '16 at 20:31
  • \$\begingroup\$ I'm not sure I understand that diagram as I first thought. If the switches are in opposite states to each other (e.g. imgur.com/a/I0VOY) then the light still turns on. I think that there may be a little more to this than meets the eye. Regardless of the state of the door switch, if I flip the bed switch then the light changes (from on to off or off to on) and vice versa. \$\endgroup\$ – Archie Roques Sep 15 '16 at 21:24

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