Author Topic: Oscillator for discrete digital clock  (Read 8685 times)

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Offline richard.cs

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Re: Oscillator for discrete digital clock
« Reply #25 on: February 19, 2018, 12:10:12 pm »
If you want to avoid lots of dividers I think your options are either a mains-derived timebase (implemented as either a receiver injection locking an oscillator or a direct connection), or a tuning fork oscillator.

If you wanted to go for the tuning fork approach the oscillator only needs one transistor. 440 Hz tuning forks are most common but a quick google search found these: https://colourofsound.org/shop/sound-therapy-instrument-shop/tuning-forks/otto-tuning-forks-32-hz-64-hz-128-hz/ which go down to 32 Hz. Convenient as both a low frequency and a simple binary division to 1 Hz. They would probably need calibrating.
 

Offline ogden

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Re: Oscillator for discrete digital clock
« Reply #26 on: February 19, 2018, 12:11:26 pm »
Electromechanical pendulum running at > 1Hz, like 4Hz? IMHO it will add eye catching value to the thing you are building.
 

Offline NivagSwerdna

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Re: Oscillator for discrete digital clock
« Reply #27 on: February 19, 2018, 01:23:18 pm »
I built one using discrete NOR logic. I blogged about it, and all of the schematics are available on github: ornotblog.blogspot.com


Quote from: From Quoted Blog
Conclusion
I'm glad its over

 :-DD
 
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Offline Zero999

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Re: Oscillator for discrete digital clock
« Reply #28 on: February 19, 2018, 01:54:17 pm »
The lowest frequency crystal, commonly available is 20kHz.

Here's a transistor clock project, which uses the mains frequency and a similar frequency divider circuit, to the one I posted previously.
http://ch00ftech.com/2012/07/10/transistor-clock-part-2-prescaler/
 

Offline TomS_

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Re: Oscillator for discrete digital clock
« Reply #29 on: February 19, 2018, 02:43:24 pm »
Quote from: From Quoted Blog
Conclusion
I'm glad its over

 :-DD

That project took more than enough of my life away.  ^-^
 

Offline BrianHG

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Re: Oscillator for discrete digital clock
« Reply #30 on: February 19, 2018, 02:48:08 pm »
If you are looking for a low frequency crystal, I dont know if it would work or how stable it would be, but, maybe, as an experiment, try using that large crystal from one of those BBQ spark igniter.  It's got to be low frequency, and high voltage.
 
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Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #31 on: February 19, 2018, 05:57:05 pm »
What drive me to do something like this is that I do want to dive to the diode logic circuits, just for fun. So basically my plan were to first design it with common logic gates (clock is basically just counters and some resets) and then design one of each in diode logic or diode transistor logic (inverted) gates. The rest should be "just" assembling with the standard parts.

How one would turn that mechanical tuning fork as electromechanical oscillator. edit: http://kt4qw.com/shortstories/project.htm
That actually might be a cool thing, gets the constant buzz for free.  ::)
« Last Edit: February 19, 2018, 06:02:44 pm by Vtile »
 

Offline Ian.M

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Re: Oscillator for discrete digital clock
« Reply #32 on: February 19, 2018, 06:46:17 pm »
 If you are really dead set on not using mains frequency for a reference, you can get 128Hz tuning forks, though you''l need an ordinary tempered steel one not a stainless steel or non-ferrous one.   However that's still 7 stages of binary dividers + the oscillator itself ad a buffer transistor to get a squarewave, so 16 transistors just for a 1Hz clock signal.   Then you will need to ovenise it as the tuning fork frequency will be significantly temperature sensitive, and purge the oven with inert gas and hermetically seal it to reduce long term drift.
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #33 on: February 19, 2018, 06:53:17 pm »
If you are really dead set on not using mains frequency for a reference, you can get 128Hz tuning forks, though you''l need an ordinary tempered steel one not a stainless steel or non-ferrous one.   However that's still 7 stages of binary dividers + the oscillator itself ad a buffer transistor to get a squarewave, so 16 transistors just for a 1Hz clock signal.   Then you will need to ovenise it as the tuning fork frequency will be significantly temperature sensitive, and purge the oven with inert gas and hermetically seal it to reduce long term drift.
;D No easy route to perfection. Yeah, these cheaper forks seems to be all aluminium or stainless, found one 128 Hz fork made from steel, but the cost is around 40€ .. I did hope there would have been some sand crystal oscillator down to some kHz, but nope. The time nuttery of mine is only for a few weeks per minute. Not a millenia.  :) Maybe I should first make my own tuning fork.  :popcorn:

PS.. Or cannibalize Omega Constellation Chronometer they seems to have 300Hz electromechanical vibrator (tuning fork).  :-DD
« Last Edit: February 19, 2018, 07:00:47 pm by Vtile »
 

Offline richard.cs

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Re: Oscillator for discrete digital clock
« Reply #34 on: February 19, 2018, 07:07:35 pm »
I found some German-made steel 128 Hz tuning forks on ebay for £17 when I looked earlier. It is possible to couple into a non magnetic one but the conventional design assumes magnetic. The alternative methods include acoustically coupling in through the air next to the tines or a direct mechanical coupling into the bottom of the fork with something like a piezo transducer. You can couple out acoustically or optically.
 

Offline Zero999

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Re: Oscillator for discrete digital clock
« Reply #35 on: February 19, 2018, 07:14:25 pm »
If you are looking for a low frequency crystal, I dont know if it would work or how stable it would be, but, maybe, as an experiment, try using that large crystal from one of those BBQ spark igniter.  It's got to be low frequency, and high voltage.
I don't think that would be suitable. The crystal inside a BBQ igniter is long and cylindrical and is completely the wrong shape for a timing crystal, which should be tuning fork shaped or a thin bar.
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #36 on: February 19, 2018, 07:27:40 pm »
I found some German-made steel 128 Hz tuning forks on ebay for £17 when I looked earlier. It is possible to couple into a non magnetic one but the conventional design assumes magnetic. The alternative methods include acoustically coupling in through the air next to the tines or a direct mechanical coupling into the bottom of the fork with something like a piezo transducer. You can couple out acoustically or optically.
But isn't one important part of the traditional magnetically coupled design that it also gives energy to the fork to continue vibration? At least that is what I think what is happening there, with piezo or acoustic coupling that re-arming energy would be much more complex to get it right I would assume.
 

Offline Kalvin

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Re: Oscillator for discrete digital clock
« Reply #37 on: February 19, 2018, 07:30:07 pm »
In the 80's this oscillator problem would have been very easy to solve. It didn't matter what kind of crystal radio you built, the Radio Moscow was the loudest station to be heard anyway. It was like 50 Hz hum which was everywhere. Nowadays, there may be some other more useful radio stations available which could be used as a timebase. So, a simple 60 kHz regenerative receiver and a divider could be used as a timebase yielding a frequency uncertainty of less than 1 part in 10E12? https://en.wikipedia.org/wiki/WWVB :)
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #38 on: February 19, 2018, 07:33:30 pm »
..This is getting out of control.. :P

Hmm... I wonder if one could build a electromechanical capacitive vibrator, like a tuning fork kind of.. 

Hmm... Hmmmmm....
« Last Edit: February 19, 2018, 07:36:17 pm by Vtile »
 

Offline ogden

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Re: Oscillator for discrete digital clock
« Reply #39 on: February 19, 2018, 07:39:46 pm »
..This is getting out of control.. :P

Hmm... I wonder if one could build a electromechanical capacitive vibrator, like a tuning fork kind of.. 

Hmm... Hmmmmm....

It's 32KHz watch crystal oscillator. They are tuning forks and they are capacitive vibrators:


 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #40 on: February 19, 2018, 07:40:52 pm »
..This is getting out of control.. :P

Hmm... I wonder if one could build a electromechanical capacitive vibrator, like a tuning fork kind of.. 

Hmm... Hmmmmm....

It's 32KHz watch crystal oscillator. They are tuning forks and they are capacitive vibrators:


Oh dang.  :palm: Circle is closed.
 

Offline ransonjd

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Re: Oscillator for discrete digital clock
« Reply #41 on: February 19, 2018, 07:43:29 pm »
You might be able to get two crystals separated by a few tens of hertz, mix their outputs, and get a nice low frequency out. The timing accuracy won't be great, but it would be pretty easy to do with discretes.
 

Offline ogden

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Re: Oscillator for discrete digital clock
« Reply #42 on: February 19, 2018, 07:49:32 pm »
You might be able to get two crystals separated by a few tens of hertz, mix their outputs, and get a nice low frequency out. The timing accuracy won't be great, but it would be pretty easy to do with discretes.

It will not work. Crystals happen to drift, one could drift faster than another. Could be so that one day clock is running 2x faster and another it is running 20x slower  :-DD
 

Offline Rerouter

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Re: Oscillator for discrete digital clock
« Reply #43 on: February 19, 2018, 07:50:05 pm »
While sacrificing accuracy compared to a crystal, a few automotive clocks used a pendulum oscillator, this was a ring with a magnet attached at 1 point, it had 2 drive coils and 1 sense coil, and a restoring spring.

When the magnet went past the sense coil in 1 direction it gave a positive pulse, in the other a negative pulse, which drove the transistors operating the drive coils which gave it a small kick to keep it moving.

I have only repaired 5-6 of these in the past, however almost all of them operated at 2 Hz, 
 
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Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #44 on: February 19, 2018, 07:51:25 pm »
You might be able to get two crystals separated by a few tens of hertz, mix their outputs, and get a nice low frequency out. The timing accuracy won't be great, but it would be pretty easy to do with discretes.

It will not work. Crystals happen to drift, one could drift faster than another. Could be so that one day clock is running 2x faster and another it is running 20x slower  :-DD
That would be like the compass of Cpt. Jack Sparrow. Hmm... Peanuts.

What about quartz oscillator... A hourglass with electromechanical motor to turn it over.
« Last Edit: February 19, 2018, 07:54:50 pm by Vtile »
 

Offline ransonjd

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Re: Oscillator for discrete digital clock
« Reply #45 on: February 19, 2018, 08:03:06 pm »
Quote
It will not work.

It's probably not that bad. I'm betting you could keep it within 20% of ~50Hz. And your next project could be a temperature chamber to stabilize your clock.  :-+
 

Offline Zero999

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Re: Oscillator for discrete digital clock
« Reply #46 on: February 19, 2018, 08:09:54 pm »
You might be able to get two crystals separated by a few tens of hertz, mix their outputs, and get a nice low frequency out. The timing accuracy won't be great, but it would be pretty easy to do with discretes.

It will not work. Crystals happen to drift, one could drift faster than another. Could be so that one day clock is running 2x faster and another it is running 20x slower  :-DD
Yes that won't work. I actually thought of it before but didn't post it because it was a dud idea. Look at the stability figures for a crystal. A reasonable one would be +/-3 ppm. Now take two crystals, say 30000Hz and 31000Hz, in the hope you can mix them to get 1kHz. Suppose the 30kHz one is just 1.5ppm too slow, that would be 29999.955Hz and the 31kHz one is just right. That gives a beat frequency of 1000.045Hz, which is 0.045Hz or 45ppm off 1kHz: much worse than the 30kHz crystal. In reality, it's likely to be much worse than this!
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #47 on: February 19, 2018, 08:10:06 pm »
Actually, could the mass of the d'arsonval movement be used as a pendulum... It could work. It should.
 

Offline Kalvin

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Re: Oscillator for discrete digital clock
« Reply #48 on: February 19, 2018, 08:13:46 pm »
Use your pulse as time base, and relax. If you notice that the clock goes too slow, your pulse will automatically go up anyway and it will catch up.
 
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Offline jmelson

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Re: Oscillator for discrete digital clock
« Reply #49 on: February 19, 2018, 08:21:57 pm »
... It would take ~250 parts if I'm not terribly mistaken..

..But this project doesn't make a much sense anyway.  :-DD
Look in VERY old transistor databooks for diode-steered capacitor-coupled flipflops.  When distilled down from the universal JKT for to just a toggle (T) FF, I think it can be done with 10 components per FF, so that would be 150 parts for a 15-stage binary divider.  This technology was not used after, maybe, 1965 or so, so you need something like the GE transistor databook from before that.  They had a bunch of sample circuits in the back.

I tried to build one of these when I was a kid, but didn't really have the test gear to even tell if it worked.  So, I built one a few years ago with modern components, and it works fine.  Pretty slow, but I think the rise time was about 50 ns, fall time (with transistors conducting) was better.

Jon
 
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