Electronic – sensor for counting the number of cards in a flipping scorecard?

infraredproximity-sensorrfid

I have a stack of cards and want to know how many cards are in the stack at any given time. Any thoughts on how I might be able to do this? Would it be possible for me to put a tag on every card and then use some type of sensor below the cards which could count the tags above it?
The cards are suspended from rings like this:

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While there was a prior question that was similar, it does not appear there were any answers that came out of that question.

Best Answer

Magnets?

Put a tiny magnet on each leaf, in a different position. Put two hall sensors behind, attached to the wall. When someone flips a leaf, the magnetic field will change detectably.

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