Interlocking concept

Problem: Design an electric circuit in which when we press START button the Conveyer belt 1 (C.B.1) is ON and Proximity Sensor 1(P.S.1)  sence 5 small boxes. After 5 boxes drop on large box Conveyer belt 1 STOP and C.B.2 start. When large box under droping position of small box, C.B.2 STOP and C.B.1 START again.

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