Scientific experiment to determine the existence of paranormal phenomena

this wouldn't prove anything.

of course you are moving the planchette subconsciously, THAT'S THE WHOLE POINT.

the focus of most occult sciences is to learn to communicate with and to control your subconscious mind.
that's how the planchette is supposed to work - the entity communicates with your subconscious, which then moves the planchette.

it's not supposed to be telekinesis or anything like that. the user is moving the planchette, the entity is simply guiding him by relaying information through the subconscious mind.

I think the problem with doing that would be that electrical signals would still be generated because your arms still have to move. It would be extremely difficult to calculate the difference between somone just moving their arms with the glass, and someone actually pushing the glass.