=Electronics Hardware Questions=

Q: The circle can rotate clockwise and back. Use minimum hardware to build
a circuit to indicate the direction of rotating.

A: 2 sensors are required to find out the direction of rotating.
       They are placed like at the drawing. One of them is connected to the data input of D flip-flop,
        and the second one - to the clock input. If the circle rotates the way clock sensor sees the light
        first while D input (second sensor) is zero - the output of the flip-flop equals zero, and if D input
        sensor "fires" first - the output of the flip-flop becomes high.