Positioning control system for alphanumeric displays

In a changeable sign, apparatus for positioning a plurality of display devices in individually selectable rotative positions, a common drive shaft for all of said devices, a reversible motor connected with the drive shaft, a separate clutch means for each device adapted to be engaged for coupling the respective device to the drive shaft, selector means for producing a desired position signal for each device, shaft position encoding means connected with said drive shaft and adapted to produce a shaft position signal, motor control means connected with the shaft position encoding means for energizing the motor in a reverse direction to drive each device to a home position and energize it in a forward direction when the home position is reached, said encoded means being connected with said selector means to cause the selector means to produce a command signal when the shaft position signal bears a predetermined relation to the desired position signal for each device, clutch control means connected with the clutches and the selector means and being responsive to the command signals for selectively engaging each of the clutch means to couple the respective devices to the shaft during shaft displacement corresponding to the rotational distance between the home position and the desired position for the respective device.