Imagine a disk spinning like a record player turn table. Half of the disk is black and the other is white. Assume you have an unlimited number of color sensors. How many sensors would you have to place around the disk to determine the direction the disk is spinning? Where would they be placed?

Answer:

There are only two sensors required. Place sensor close together. Reset sensors. The switching sequence of two sensors will indicate the directional rotation of the disk easily.

This is common approach in industrial automation.







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