Hi,

I'm really new to electronics and have a little project to start learning, I came across this forum which I hope can help.

The idea is to make a desktop clock.

I have made two cardboard disks, one for hours and one for minutes.

The disks are circles with the numbers around the outside, this then clips onto another bit of cardboard with a window to show the current hour / minute

I've had a look into how I can spin the disks and read about stepping motors and timers plus variable resisters to slow the motor down to the right speed but don't really know where to start. I don't want to buy all the wrong stuff and waste a stack of money, even though it should be cheap enough?


Ideally, something that just turns x degrees every hour would be good, I guess there are loads of ways this can be done?

Any advise would be appreciated,

Here is the drawing to explain how the disks work, this is just the "hour" one:

Thanks

 

In fact, if you think of it, the stepper of any disk is to be iddle most of the time and just move quite "fast" when rotating its disk to bring the next figure to the window. You do not want, I guess, two figures showing at the same time in a window, no matter they are hours or minutes. Not pleasant to see and most probably, confusing.

The "hours" stepper will do it, once in 60 minutes. The "minutes" stepper will do it once in 60 seconds.

You need kind of a somewhat complex setup with logic gates and timers to: adjust the time once (upon start), keep the time and show the sucessive values.

Otherwise, you will need a micro.

Could you rethink your original idea?

 

Thanks for the quick reply!

That does sound quite complex,

I was hoping I could attach a motor on the back of the spinning disk and make it rotate x degrees every 1 hour with a timer perhaps?

To set the time at the beginning, just manually rotate the disk to the correct hour and start the circuit via a switch on the hour.

I guess I could work on the hours one first and apply the same thing to the minutes spinning disk but change the degree of spin and interval time between spins.

Would that be easier to do for a first project, then move into relays etc once I have the basics understood?

 

Yes, I think it could be done. Not what I would but seems possible.

 

A stepper motor would be one way, but for simplicity you would need one with 60 x N (N=1,2,...) steps per revolution. I couldn't find one listed with a quick google .

 

Doing it mechanically would be much simpler, but not much fun if you are looking to do it electronically.

A solenoid with ratchet or an intermittent mechanism would be mechanical methods.

I believe one is called a geneva. Used on camco index tables.

The solenoid would require electronics. While the geneva drive only needs a synchronous gear motor on ac power.

 

There are a couple threads on this site that asked a similar question. It turns out there exist stepper motors with finer resolution than the typical 1.8° or 17°.

Check out this thread and the links therein.

http://forum.allaboutcircuits.com/showthread.php?t=57710

 

A stepper motor would be one way, but for simplicity you would need one with 60 x N (N=1,2,...) steps per revolution. I couldn't find one listed with a quick google .

So are you thinking to rotate 1/12 of a rotation then off, at 5 minute intervals?

Direct drive with the correct motor?

 

I built a stepper motor clock, using the Linistepper kit which is a stepper motor driver that can give 3600 steps/rev from a 200 step/rev motor;

http://www.piclist.com/techref/io/stepper/linistep/LiniClock/index.htm

Because the Linistepper contains a PIC micro on the PCB, you can program it to give very accurate timekeeping AND turn the clock hand in any way you like. (Of course that requires the ability to program a PIC.)

 

So are you thinking to rotate 1/12 of a rotation then off, at 5 minute intervals?

Yes. A 60-steps-per-rev stepper would make life simple. Alas, the common 48-step or 200-step motors would call for quite a bit of electronics or a micro to get 30 degree increments.

A highly-geared DC model motor, with an angle-encoder on the output shaft, is arguably the next simplest solution.

Cheapest solution of all, using no external electronics, would be to use two standard quartz clock mechanisms from the dollar store; one for the minutes disc and the other for the hours disc.

 

... Alas, the common 48-step or 200-step motors would call for quite a bit of electronics or a micro to get 30 degree increments.
...

Sorry to correct but 360' divided by 30' is twelve positions, a common 48 step stepper can be run at full-step 48 steps/rev or half-step 96 steps/rev, and in both cases divide equally by 12.

Re 200 step/rev motors; the Linistepper kit can drive a 200 step motor in these microstepping modes;
200
400
1200
3600
(note the last two can also be equally divided by 12).

Normal IC microstepping drivers are limited to these modes;
200
400
800
1600
3200
(note that none can be divided by 12).

 

I don't mind being corrected. My bad; I was confusing the hours and minutes angle increments. Yes, a 48-stepper will do nicely for the hours dial (30 degree steps). The problem would arise in getting 60 steps per rev if (albeit unlikely) the OP wanted 1-minute resolution rather than 5-min on the mins dial.

 

I don't mind being corrected. My bad; I was confusing the hours and minutes angle increments. Yes, a 48-stepper will do nicely for the hours dial (30 degree steps). The problem would arise in getting 60 steps per rev if (albeit unlikely) the OP wanted 1-minute resolution rather than 5-min on the mins dial.

As it happens, a while ago there was a thread here on a very similar topic, where someone wanted to make a second hand for a clock (60 steps per revolution) using a 48-step motor. I demonstrated that it could be done, and made a video of the device in action:
http://www.youtube.com/watch?v=EGwNYo69y2o

Those skilled in the art will recognize the reason why the motor makes a whining sound on 4 steps out of every 5, but then is silent during the 5th step.

 

I demonstrated that it could be done

Nice. Even nicer with a 60-step motor to do the job .