We all know about the system of two switches controlling one lamp(at the ladder) like the picture. Could you help me design a system of four switch to control one lamp ? thanks

enter image description here

  • \$\begingroup\$ So if the light is off, changing one switch will turn it on? Also if the light is on, changing one switch will turn it off? The switches have only two positions? (Do you mean "stairs", and not "ladder"?) \$\endgroup\$ – gbulmer Sep 15 '14 at 14:00
  • \$\begingroup\$ Yes, like you mean, Gbulmer \$\endgroup\$ – T.Nhan Sep 15 '14 at 14:07
  • \$\begingroup\$ You need a DPDT switch in the middle that flips the two lines. \$\endgroup\$ – George Herold Sep 15 '14 at 14:08
  • \$\begingroup\$ @GeorgeHerold - Are you aiming to give a helpful hint? That will be three switches, not four. \$\endgroup\$ – gbulmer Sep 15 '14 at 14:14
  • \$\begingroup\$ @gbulmer, Oh sorry once you've done 3 expanding to any number is easy. (Well, you need a lot of wire to connect all the switches together.) \$\endgroup\$ – George Herold Sep 15 '14 at 14:19

To achieve your goal you will either need some DPDT switches or an "inverter" switch, I don't really know the English word for that.


simulate this circuit – Schematic created using CircuitLab

Above you can see a DPDT switch wired as an "inverter" switch. Either A is connected to 0, and B to 1, or A is connected to 1 and B to 0. You can add as many inverters as you want between the SPDT switches of your schematic, if the light is on, i.e. there is a path for the hot wire to arrive at the lamp, changing the state of any inverter in the path will break it, and conversely if there is no path changing the state of an inverter will make it.

Inverters were widely used some years ago, nowadays the trend is using push buttons and a latching relay: you wire all your push buttons in parallel, when you press any of them the relay toggles its state.


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