floppy centring unit

In modern disk drive mechanisms, as, for instance, the TEAC FD55x, the motor starts automatically when a disk is inserted into the drive. When the lid is closed, the motor stops again. This arrangement ensures bet- ter centring of the disk. Better cen- tring means less wear on the centre fixing hole, the life of the disk is extended, and read/write errors owing to eccentricity off the disk are prevented. Owners of older drive mechanisms, such as the BASF 6106, can incor- porate that facility with the circuit pro- posed here. The signal from the write protect phototransistor is used to determine when a disk is being inserted (this signal is normally gated when the drive is closed), and to start the motor for the total period of 5V floppy centring unit IC1 MMV1 = %ICI = 4098 C1 monostable MMV1. The SPEED signal is not absolutely necessary: it stops the motor direct when the lid is closed. If it is not used, pin 3 must be connected to the +5 V line. The motor will then run for the du...