The hard disk drive’s read/write heads are maneuvered across magnetic platters using a linear motor. This motor comprises a coil that moves within a robust magnetic field, controlled by sophisticated electronics to swiftly position the heads accurately. With a significant number of hard disk drive failures, enthusiasts can easily acquire one for repurposing. Due to the motor’s extensive stroke and force capabilities, we utilized it in a unique clock project.
Applying a DC voltage to the coil causes the arm to abruptly move from one end to the other. Reversing the voltage polarity shifts the arm in the opposite direction. A PC can regulate the voltage applied to the coil through a Darlington circuit (refer to Figure 1).
Computer Interface: Centronics Port Configuration
In this setup, a specific pin (K1) of the Centronics port on the computer is utilized to drive the circuit. The control signal originates from pin 2 of the Centronics connector, which links to bit 0 of port H378. Pin 19, serving as the ground, is connected to the control circuit’s ground line. To power the system, a robust AC power adapter delivering a minimum of 2 A is essential.
Unconventional Mechanical Design: Innovative Clock Structure
The clock’s mechanical design deviates from the norm. It incorporates a curtain rail positioned at an inclined angle. Along this rail, a steel ball from a ball bearing is propelled upwards and rolls back down under its weight. When the ball is struck with a force contingent on the time of day, it travels a specific distance along the rail. Observing the ball’s movement enables approximate time reading from an hour scale marked along the rail’s length.
Impact Generation and Time Calculation: Repurposed Hard Disk Drive Component
To generate impact on the ball, a discarded hard disk drive’s head motor is repurposed. The ball rests against the motor’s arm when it’s at the rail’s lowest point. The computer calculates the impact force and drives the motor for a predetermined duration. The clock’s software is designed using Visual Basic and features a straightforward structure, extensively documented for clarity.
Now for some practical details on the clock:
Rail length approx. 160 cm (5’ 5”)
– Height difference (top/bottom) approx.
10 cm (5”)
– Ball diameter 17 mm (11/16”)
– Head motor coil resistance 5–15 Ω (depending on hard disk model)
Coil voltage 5–12 V (depending on coil resistance)
The hours scale on the rail must be determined experimentally after first adjusting the
impact for 12.00 h so the ball nearly reachesthe highest point of the rail.