OK two things you could do:-
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Add a wheel and opto slot detector to your DC motor and count the pulses so you know where you are. This is like the old type of mouse worked, the one with a ball.
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Use something like a 74LS148. It's a 8 line to 3 line Priority encoder to gather your sensors into a few inputs. As you want 12 inputs you will have to cascade two together, it shows you how in the data sheet.