# What is the simplest analog circuit for integer addition modular 2?

This probably is a rudimentary question. I would like to have a simple analog (switch) circuit for addition modular 2, or $a_1+a_2+\cdots +a_n$ (mod 2). Certainly, digital transistors can accomplish this, but I would prefer analog devices if the circuit is simpler. In practical terms, I would like to design a switch circuit to control a light, where fixing all other switches, any one of them can switch the light on and off. For $n=2$ or 2 switches, someone earlier has already suggested using two back to back single-pole-double-throw switches.

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May not be the simplest, but implementing n input xor gate using transistors is a solution. – nidhin Jul 12 '14 at 14:52
@nidhin, yes, but I would prefer simpler analog circuit. – Hans Jul 12 '14 at 15:34

For 4 places see below: -

simulate this circuit – Schematic created using CircuitLab

For 3 places remove one of the two pole switches. For more than 4 just keep repeating the 2 pole switches.

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Dang it. I just spent an hour noodling on this and just came up with this. Congrats for beating me to it. At least I have the satisfaction of solving this interesting house wiring issue. Btw, was this a well known design you've known for years or did you just come up with this? +1 – horta Jul 12 '14 at 16:56
@horta - well done for figuring it out dude but on this occasion knowledge has beaten intelligence LOL – Andy aka Jul 12 '14 at 17:36