"Propeller Clock" Mechanically Scanned LED Clock
Seven light emitting diodes spin, giving the illusion of numbers in the air.

Top View

Side View

This is the first clock I ever built. I've built a few LED signs, but they get boring because I already know the message.

How this clock works:
A motor spins the "propeller", and a small microprocessor keeps track of time and changes the pattern on seven LEDs with exact timing to simulate a 7 by 30 array of LEDs. It is an illusion, but it works nicely.

If you want to build this clock, you will need a few things, including:
  Skill with motors and mechanical things.
  Prior electronic experience.
  A dead VCR or floppy drive or other source of a suitable motor and miscellaneous parts.
  A programmer that will program a PIC16C84 or 16F84 microprocessor.

I have provided (almost)everything else:
The Next Page with drawings and plans.

mclock.txt A full description how to build it.
mclkpart.txt The parts list.
mclock8.asm The source code in Microchip MPASM format.
mclock8.hex The hex code ready to load into a PIC16C84 or 16F84 chip.
mclksch2.gif A large and very readable schematic diagram.
mclkmoto.gif A drawing of the modifications to the motor.

If you can't get that kind of motor, you can use the motor from an old disk drive. This page has a lot of pictures and will take some time to load. If you use a disk drive motor or any other DC motor with brushes 180 degrees apart, you'll need the slightly revised code:
mclockt3.asm The source code.
mclockt3.hex The hex code ready to put in a chip.

If you don't have any way to put the program into a PIC 16C84 or 16F84 chip, you can build your own programmer.

Printed Circuit Board Layout for a version of the clock.

The hardware design and software are covered under the GNU General Public License.


Frequently Asked Questions:


What’s this .047 FARAD capacitor??


You can get them many places, including memory capacitors at Jameco Electronics.




What’s a Berg connector?


What’s a Kleenex? :-) The PC board side is sometimes called a “header”. The lights and buttons hooking to computer motherboards use them. The pins are .025” square, on .1” centers. The female end is composed of crimp terminals fit into a plastic housing. An example at Jameco.




I saw a big version of this at a store but it was different. Have you seen it?


Yes, I’ve seen a lot of “persistence of vision” clocks in recent years. I made this one in 1996, so I think they all copied me :)




My VCR head motor has lots of wires. Which ones do I use?


I didn’t use a head motor. I used a reel motor. It only has 2 wires and runs on DC.




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