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# How to design the simplest circuit that has three inputs?

It produces an output value of 1 whenever exactly one or two of the input variables have the value of 1; otherwise, the output has to be zero ( if all three inputs = 0 or 1 )

### 2 Answers

- billrussell42Lv 71 decade agoFavorite Answer
A simple solution would be a 3 input AND gate to detect all 3 inputs =1, and a 3 input low true AND gate to detect all 3 inputs =0, OR those two outputs together to get NOT TRUE output, invert that for the TRUE output. So that is 3 gates.

It can also be done in the analog world with an analog adder to add the high voltages (5v) together, with a factor. You can pick 4 resistors so that the output is (for example) 0V, 1v, 2v, 3v, for 0, 1,2 ,3 inputs high. then you just need a dual limit comparator to look for a voltage >0.5v and <2.5v to signal true. This seems more complicated than the 3 gate solution above.

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