There's a circular rotating disc composed of two semi circles, one white and the other black. You are given sensors that you can place directly above

There's a circular rotating disc composed of two semi circles, one white and the other black. You are given sensors that you can place directly above the disc. These sensors send a 0 when the region below it changes from white to black and 1 when it changes from black to white. The speed of rotation of the disc is not predictable
a. What is the minimum number of sensors you need to determine the direction of rotation? Also draw a state change diagram
b. What is the optimal placement of the sensors in order to optimise the time taken to detect the direction of rotation
c. If you are given just one sensor, what additional constraints will you bring in to the equation?

2 sensors, put sensor A on the twelve’o clock, put sensor B on the three’o clock
If firstly A gets a value and then B gets a value, if(A.value==B.value) clockwise
If firstly A gets a value and then B gets a value, if(A.value!=B.value) anticlockwise
If firstly B gets a value and then A gets a value, if(A.value==B.value) anticlockwise
If firstly B gets a value and then A gets a value, if(A.value!=B.value) clockwise