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=Electronics Hardware Questions=


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

2 sensors are required to indicate the direction of rotating.
They are placed like at the drawing.
One sensor 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.