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Forgive my ignorance and if this question has been asked before, but I cannot find it asked anywhere else, please read carefully before telling me it has been asked already.

I'm trying to design a system with a row of switches which each have two positions. If all the switches are in the same position, an LED illuminates. If all the switches are in the opposite position, a different LED illuminates. If any one of the switches are not in the same position as the others, no lights illuminate. See image that should clarify this.

enter image description here

What I need to know is what kind of switch I need. I imagine I need one which has four pins on, two pairs that are entirely independant and are part of seperate circuits. When the switch is in the up position, two pins are closed to allow a circuit, and the other two pins are open. When the switch is in the down position, the bottom two pins are closed to allow a circuit and the top two aren't.

A SPDT On-On Switch like the one pictured seemed appropraite... enter image description here

... until I realised that wiring this up in series wouldn't work because it wouldn't make a difference to the next switch in the circuit which position the previous switch was in, but maybe I just need someone to explain some clever wiring to make that work.

I hope this isn't too basic a question, and someone can help.

Thanks

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  • \$\begingroup\$ Are the switches supposed to switch anything else apart from the LEDs? If they're not the circuit seems a bit pointless. \$\endgroup\$
    – Transistor
    Jun 27 at 21:00
  • \$\begingroup\$ @Transistor wire switches randomly so top is bottom and vice versa and it becomes a binary sequence "key". All correct = green, all incorrect = red. Essentially two sequences with different functions. | Or an interlock or voting system - all go or all safe. \$\endgroup\$
    – Russell McMahon
    Jun 27 at 23:39
  • \$\begingroup\$ The circuit voltage and load needs to be defined too. \$\endgroup\$ Jun 28 at 0:04
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A soution using DPDT (double-pole double-throw) switches.

schematic

simulate this circuit – Schematic created using CircuitLab

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ErikR's solution is nice because current only flows when a LED is lit.

But if you're willing to dissipate power, even when LEDs are OFF, this works with a simpler switch type outlined by OP:

schematic

simulate this circuit – Schematic created using CircuitLab


Interesting how the series string seems the first "goto" kind of circuit that comes to mind. Shorting LEDs somehow seems less-obvious.

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SPDT On-On switch should suffice just fine.

You need to wire it so that a switch in up position turns off the red LED, and a switch in down position turns off the green LED.

Thus, if all switches are up, nothing turns off the green, and if all switches are down, nothing turns off the red LED. Any other combination of switches being up and down will turn off both LEDs.

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