Gadget Freak

Check out this inventive use of an MCU and stepper motor by one Alan Parekh.

This great looking gear clock tells the time in a unique way. A PIC 16F628A microcontroller with an external 20MHz crystal oscillator times a stepper gear, which drives a minute display, which also drives an hour display...

It's 11:21 in the still above, by the way.

Details of Alan's project can be found here: http://alan-parekh.com/projects/gear-clock/

Of the motor, he writes:

The motor is a unipolar stepper motor that has been harvested from an old 5 1/4 inch floppy drive. This is the motor that used to move the read write heads back and forth, to get one of this size and power you'll need to find a nice old one. There are many sizes and styles of steppers so it may take a bit of digging to find a usable one. Modern floppy drives don't have steppers with this level of torque.

This motor moves 1.8 degrees per pulse which means that with 200 pulses it will make one full rotation. Since it's a unipolar motor it is simple for the PIC to drive it with only 4 transistors. You will also need to be aware of motors with different number of pulses per rotation however 200 is the most common.

You can view a general schematic of the design, and you can also download the HEX file for the chip from Alan's page.

The MCU, amid the casing.


And the stepping motor is pictured below.