> No motor, noise is only present when the pot. moves.
> When the movement stops I get a nice crisp line on the scope

If you were doing this with a PIC to detect the end of an event of
indeterminate length -

Say the timer is set to rollover or reach a certain count after 0.5s. Any
noise (ie change) on an input resets the timer. Only when there's been
no noise for 0.5s will the timer complete its count

Alternative is to continuously poll the ADC looking for stability

This may be useable depending on the movement and timing patterns
of the cylinder

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