Introduction: Gear Clock

The heart of the clock is a PIC 16f628A microcontroller (PDF). This microcontroller has an internal oscillator however an external 20MHz crystal oscillator is being used since it will have to accurately keep track of time for weeks and months. The microcontroller is interfaced to two buttons and one motor.

For more details have a look at the project Website.
alan-parekh.com/projects/gear-clock

The Gear Clock Kit is now available. Have a look at our kit page for more details. If you have a CNC machine you can cut your own gears and just purchase the electronics for the clock.



Step 1: Cut and Paint the Gears

The gears are made out of MDF. They were painted to have a metallic look however the look I was going for was not achieved. Initially I was thinking of making the gears look like they were made of metal and left to rust for a few dozen years. I found some cool products that would give me that rusted effect but they were a bit too expensive. I settled for a can of Krylon Black Metallic Hammered Finish paint. The sample on the lid is a very nice black with subtle bit of gray. I think this might be from a bad batch since the final look is not as black as it should be. It also made taking pictures of the final clock a bit tough since even with modest lighting the glare was horrible.

The gear arrangement is as follows:

  • 9 tooth motor gear
  • 72 tooth minute gear with a 24 tooth secondary
  • 72 tooth intermediate gear with a 18 tooth secondary
  • 72 tooth hour gear

To achieve the correct timing the 9 tooth motor gear is advanced 4 steps every 9 seconds. By moving 4 steps at a time the motor routines can be simple since the motor is always at rest with the same coil energized.

Step 2: Construct the Clock Electronics

Microcontroller

The brains of this project is a PIC 16F628A microcontroller. It keep track of time and activates the stepper motor when needed.

Buttons

The interface is very simple, it consists of two buttons. When the left button is pressed the clock advances time using the motor. When the right button is pressed the clock decrements time using the motor. The only issue is when you need to correct time by many hours you would have to keep the button pressed for a long time. The stepper motor is also always energized to prevent the gears from slipping. To overcome this issue when both buttons are pressed the stepper motor is deenergized and the minute gear can be spun freely.

Motor

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. 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 bipolar motor it is simple for the PIC to drive it with only 4 transistors.

Code

The code is basically split into two sections, there is an iterative loop that monitors the buttons for a change in state and checks if the internal clock has crossed the 9 second mark. If one of those conditions has occurred the stepper motor is driven appropriately.

The other section of code is interrupt driven and it keeps track of time. An interrupt is triggered every 0.1 seconds and adjusts an internal clock as needed. There is a true running clock inside, if you connect the clock PIC pin 6 to a computer serial port operating at 9600 bps you will see the internal clock values update once per second. The clock value in this case is arbitrary since it is never shown and will not be the same as what the gears are displaying but this same code will be used in future projects which will use this code display time.

Step 3: Assemble and Enjoy

All the pieces screw together, the only piece that is glued is the stepper motor into the motor holder.


Comments

author
Junky228 (author)2012-10-09

I know this is a bit old now, but is the design scalable?, I'd like to downsize this design to be about 8 inches wide.

author
REA (author)2010-10-21
using the picture, i was able to crudely model the clock in Inventor.

here are the files

Image.png
author
abbtech (author)REA2010-10-21

Nice!

You can get the CAD here if you want.
http://alan-parekh.com/projects/gear-clock/

author
REA (author)abbtech2010-10-22

i kept trying those files to get the proper dimensions but they wouldnt work in DWG Viewer, Inventor, or AutoCAD (all the most current version).

author
Rob K (author)2010-04-14

For some reason I cant get any of the DXF files to open on this computer. Photoshop CS2 , AutoCAD 2009, Inventor 2010.

Ill give it a try on the schools computer.

author
abbtech (author)Rob K2010-04-14

I just downloaded the zip from the site and opened it. Please re-download the file I think something is corrupted in yours.
http://alan-parekh.com/projects/gear-clock/

author
REA (author)abbtech2010-10-05

AutoCAD 2011 cant open them either.

author
abbtech (author)REA2010-10-05

Not sure what the problem could be. The files open properly on my side and many people have used the same files to make the gears. I just exported the DXF from Artcam so it might be the way it formats the file...

author
Rob K (author)abbtech2010-04-14

I was only able to view the DXF files on AutoCAD, and Inventor when I imported them into MicroStation then resaved them as a DXF in another folder.

Weird.

author
Rob K (author)Rob K2010-04-14

Same on the school computers also. Autocad 2008.

Invalid or incomplete DXF input -- drawing discarded

author
mathman47 (author)2010-08-09

I have the kit from Alan, but haven't built it yet. Glad I ran across this I*. I've been trying to come up with ideas for colors and am thinking now about using one of the Krylon spray cans for a textured effect. Do you know if you can put another color on top? Great job. I love clocks. As I sit at my desk I can see 12 and I have a few to build yet!

author
Ender2007 (author)2010-03-27

How do you cut the gear?

author
abbtech (author)Ender20072010-03-27

I used a CNC machine but you could print the design and cut it with hand tools.

author
Ender2007 (author)abbtech2010-03-28

Thank you for the reply.
I should have been clearer with my question.

I would love to to the same with a CNC but I lack experience.
What kind of CAD did you use to generate the gears?
And how did you process them to the CNC?


Thanks.

author
abbtech (author)Ender20072010-03-28

I used a Fireball V90 CNC machine and cut them using Mach3. You can download the files to cut on your CNC machine here.
http://alan-parekh.com/kits/gear-clock-kit/

author
Ender2007 (author)abbtech2010-03-29

Thank you so much!
Going there right now...

author
Doc Holliday (author)2010-03-14

As a first step, how do I create really accurate gear patterns without expensive tols and training?

author
abbtech (author)Doc Holliday2010-03-14

You could purchase the gears or cut them out using a saw.

author
john3f (author)2010-01-02

The step motor used in this project is a "unipolar" type step motor, not a bipolar one. Bipolar step motors dont have a "common, ground, +V, coil split etc.." connection. Also it's not easy to drive a bipolar step motor. A bipolar stepper requires h-bridge circuit and 8 transistors for the coils to be driven.

author
abbtech (author)john3f2010-01-02

You are very right John. I have updated the page.

author
john3f (author)abbtech2010-01-03

Great. The project is really awesome.

author
abbtech (author)john3f2010-01-03

The kit version should be available in about 3 weeks. Custom boards should be in any day now... It feels like a second Christmas. :)

author
knife141 (author)2009-10-28


Very nice project!  In terms of getting a rusted metallic look on wood, I've had good luck spraying the parts with flat black, then just lightly dusting with bronze metallic paint. 

author
Killer~SafeCracker (author)2009-10-25

Good job. Now if I could just get the gears I would build.

author

Thanks. It might be made into a kit, there has been lots of interest. To be automatically notified is a kit is made available sign up here.
http://alan-parekh.com/mailing-list/

Or just keep your eye on this page.
http://alan-parekh.com/projects/gear-clock/

author
newtonn2 (author)2009-10-25

 Very cool clock! Excellent JOB!

author
robotguy4 (author)2009-10-22

You should maybe add two stationary pointers to the mix...  For accurate time reading...

author
abbtech (author)robotguy42009-10-23

That would sure help. Thanks for the idea.

author
benthekahn (author)2009-10-21

 if you put sea water on steel it will rust it over night.

author
abbtech (author)benthekahn2009-10-21

It is made of MDF though.
Check out what happens to MDF when it gets wet!
http://forum.hackedgadgets.com/viewtopic.php?t=2589

author
benthekahn (author)abbtech2009-10-22

I said that to let you know that you could just cover the gears with thin steel sheet, and rust it over night for very little cost.

author
abbtech (author)benthekahn2009-10-23

That would be a cool idea!

author
Koosie (author)2009-10-22

Woah, seriously awesome!

Looks a bit like the twin cams on a DOHC straight six.

7m-ge.jpg
author
abbtech (author)Koosie2009-10-23

LOL, it does!

author
Re-design (author)2009-10-23

First Class.

author
Doldrum (author)2009-10-22

 I don't need to tell you how awesome that is.  

author
3366carlos (author)2009-10-22

Outstanding man.  The only feedback I have is: you need a reference point on each gear  so that anybody that looks at your clock can read the time easily.

author
Chicken2209 (author)2009-10-21

 Saw this on my make rss (i think)
Really interested me mainly because I've had the idea of a planetary clock but given very limited budget and supplies i'd be limited to cardboard and an exacto knife.  MDF seems slightly better though... What programs did you use to make the gears?  The closest i had was inkscape that has a star tool that can create a gear looking shape that could function but i think its mainly for looks and not functionality. I like the use of the floppy drive motor too.

author
abbtech (author)Chicken22092009-10-21

Hi Chicken,

I used Artcam to design most of it. MDF is cheap and tough, I would use it over cardboard.

author
Chicken2209 (author)abbtech2009-10-21

How was it cut?

author
abbtech (author)Chicken22092009-10-21

On a Fireball V90 CNC machine using Mach 3.
http://hackedgadgets.com/2009/04/26/fireball-v90-cnc-router-assembly/

author
newbie2cnc (author)2009-10-21

That is an awesome clock! Could we get the files or drawings of the clock gears?

author
abbtech (author)newbie2cnc2009-10-21

I have had some inquiries about that, I will make them available in the near future on my site.

author
Phil B (author)2009-10-21

 This is nice, but I do not have access to a CNC machine.  What about a version of this project that uses wooden wheels with rubber tires driving each other by friction?

author
abbtech (author)Phil B2009-10-21

That is a good idea. As long as slipping wasn't an issue it would work very well.

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Bio: You can see my blog here: http://hackedgadgets.com and my personal site here: http://alan-parekh.com
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