E1.3 A CD player laser beam focusing system has an array of photodiodes that is used to determine if the laser beam is in focus. The laser beam focus is controlled by an input current to a lens focusing motor. A microprocessor controls the input current to the motor by comparing the output from the array of photodiodes. Complete the block diagram representing this closed-loop control system shown in Figure E1.3, identifying the output, input, and measured variables, and the control device.