Author Topic: Oscillator for discrete digital clock  (Read 8684 times)

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Offline VtileTopic starter

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Oscillator for discrete digital clock
« on: February 18, 2018, 05:13:53 pm »
Hello.

I'm wondering and pondering a new project. An all discrete digital clock. Can someone suggest me some approaches for the oscillator part of the circuit as obviously it should be fairly slow, but stable. Am I right? Or is there a nice trick to drop the typical quartz kHz oscillator pulse to something more useful for a minute counting, without piling a hundreds of parts just for that.
 

Offline zztech

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Re: Oscillator for discrete digital clock
« Reply #1 on: February 18, 2018, 05:39:26 pm »
You can build oscillator with quartz and CMOS or TTL IC's. You have to divide frequency to 1Hz.
http://www.electroschematics.com/225/1hz-generator-and-2hertz-oscillator/
This is one typical circuit. You can use also microcontroller.
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #2 on: February 18, 2018, 05:45:37 pm »
Hmm... Too many ICs..

Thank you for that idea, but no I try to avoid using any ICs even if "old" ones. All discrete basic parts crystals, diodes, transistors etc.

Is the 32kHz the minimum frequency of commercial crystals?
« Last Edit: February 18, 2018, 05:49:14 pm by Vtile »
 

Offline Kalvin

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Re: Oscillator for discrete digital clock
« Reply #3 on: February 18, 2018, 05:50:44 pm »
Looking for something like this?

https://upload.wikimedia.org/wikipedia/commons/6/6d/Transistor_Clock.jpg

No ICs included ;)
 
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Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #4 on: February 18, 2018, 05:51:42 pm »
Looking for something like this?

https://upload.wikimedia.org/wikipedia/commons/6/6d/Transistor_Clock.jpg

No ICs included ;)
Yes... But with better implementation.  ;)

That one seems to take the base clock signal from the mains. Not too exited.
« Last Edit: February 18, 2018, 06:03:13 pm by Vtile »
 

Online iMo

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Re: Oscillator for discrete digital clock
« Reply #5 on: February 18, 2018, 06:02:04 pm »
Quote
Can someone suggest me some approaches for the oscillator part of the circuit as obviously it should be fairly slow, but stable. Am I right? Or is there a nice trick to drop the typical quartz kHz oscillator pulse to something more useful for a minute counting
For a "minutes counting" (60secs period) and built with discrete components search for "fet astable multivibrator". Carefully designed (voltage stabilization, quality foil capacitors, stable resistors, transistors kept at same temperature) you may achieve +/- few minutes a day :)
« Last Edit: February 18, 2018, 06:07:34 pm by imo »
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #6 on: February 18, 2018, 06:04:13 pm »
For a minute counting with discrete components search for "fet astable multivibrator". Carefully designed (voltage stabilization, quality foil capacitors, stable resistors, transistors kept at same temperature) you may achieve +/- few minutes a day :)
That wouldn't be a clock, but a counter.  :)
 

Offline Kalvin

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Re: Oscillator for discrete digital clock
« Reply #7 on: February 18, 2018, 06:08:55 pm »
Looking for something like this?

https://upload.wikimedia.org/wikipedia/commons/6/6d/Transistor_Clock.jpg

No ICs included ;)
Yes... But with better implementation.  ;)

That one seems to take the base clock signal from the mains. Not too exited.

It should be quite easy to build a 32.768 kHz xtal oscillator and build 15 divide by two flip-flops giving 1 Hz.
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #8 on: February 18, 2018, 06:19:18 pm »
... It would take ~250 parts if I'm not terribly mistaken..

..But this project doesn't make a much sense anyway.  :-DD
 

Offline Kalvin

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Re: Oscillator for discrete digital clock
« Reply #9 on: February 18, 2018, 06:23:53 pm »
Using 0201 size passives and SOT-723 transistors it might be surprisingly small, though. Wristwatch made using discrete components! :)
« Last Edit: February 18, 2018, 06:27:52 pm by Kalvin »
 

Online iMo

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Re: Oscillator for discrete digital clock
« Reply #10 on: February 18, 2018, 06:27:32 pm »
You may buy this Watch, glue a piezo sensor on it, follow with a single fet pre-amplifier, and you get a quite precise ~few pulses per second. The cheapest way to continue with your project as far as the discrete components number is concerned   :)
« Last Edit: February 18, 2018, 06:29:26 pm by imo »
 

Online daqq

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Re: Oscillator for discrete digital clock
« Reply #11 on: February 18, 2018, 06:28:47 pm »
Quote
Is the 32kHz the minimum frequency of commercial crystals?
Certainly these days. You might find some old lower frequency ones, or have custom ones made.
Quote
... It would take ~250 parts if I'm not terribly mistaken..
I suppose that if you desperately want to avoid using a binary prescaller (32768 Hz / 32768 = 1 Hz) you could try something more exotic, like get to precission oscillators, 1 Hz apart, do the XOR of their outputs, run it through a low pass filter and get the difference. Maintaining that difference would be pretty critical and difficult. But it's possible.

You can't beat the stability of a crystal by any simple means. Sure, you can use an RC oscillator as a timebase, but that's just silly. Or, go the electro mechanical route, use a tuned fork oscillator. Or something similar.
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Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #12 on: February 18, 2018, 06:32:35 pm »
Using 0201 size passives and SOT-723 transistors it might be surprisingly small, though. Wristwatch made using discrete components! :)
:-DD

I had actually something like, which I just found in mind: https://hackaday.io/project/27410-uncon-talk-discrete-d-flip-flops
 

Offline Kalvin

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Re: Oscillator for discrete digital clock
« Reply #13 on: February 18, 2018, 06:33:51 pm »
50 Hz is everywhere. Just make a high gain amplifier and you have a timebase. No pesky xtals needed. It won't work outside nearest power line, though. But if you make a self-oscillating circuit with 50 Hz resonance and inject the amplified 50 Hz mains, it will keep accurate time near power lines, and it will keep time as "best effort" outside 50 Hz mains.
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #14 on: February 18, 2018, 06:34:06 pm »
Quote
Is the 32kHz the minimum frequency of commercial crystals?
Certainly these days. You might find some old lower frequency ones, or have custom ones made.
Quote
... It would take ~250 parts if I'm not terribly mistaken..
I suppose that if you desperately want to avoid using a binary prescaller (32768 Hz / 32768 = 1 Hz) you could try something more exotic, like get to precission oscillators, 1 Hz apart, do the XOR of their outputs, run it through a low pass filter and get the difference. Maintaining that difference would be pretty critical and difficult. But it's possible.

You can't beat the stability of a crystal by any simple means. Sure, you can use an RC oscillator as a timebase, but that's just silly. Or, go the electro mechanical route, use a tuned fork oscillator. Or something similar.
.. Or some form of PWM to voltage conversion and comparator. Outcome again would be something more like a counter. I would assume.  ???   ...part count unknown.
« Last Edit: February 18, 2018, 06:36:56 pm by Vtile »
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #15 on: February 18, 2018, 06:35:47 pm »
50 Hz is everywhere. Just make a high gain amplifier and you have a timebase. No pesky xtals needed. It won't work outside nearest power line, though. But if you make a self-oscillating circuit with 50 Hz resonance and inject the amplified 50 Hz mains, it will keep accurate time near power lines, and it will keep time as "best effort" outside 50 Hz mains.
That is interesting approach. Is that called a locking oscillator.
 

Offline Kalvin

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Re: Oscillator for discrete digital clock
« Reply #16 on: February 18, 2018, 06:37:41 pm »
50 Hz is everywhere. Just make a high gain amplifier and you have a timebase. No pesky xtals needed. It won't work outside nearest power line, though. But if you make a self-oscillating circuit with 50 Hz resonance and inject the amplified 50 Hz mains, it will keep accurate time near power lines, and it will keep time as "best effort" outside 50 Hz mains.
That is interesting approach. Is that called a locking oscillator.
https://en.wikipedia.org/wiki/Injection_locking
 
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Offline NivagSwerdna

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Re: Oscillator for discrete digital clock
« Reply #17 on: February 18, 2018, 06:42:22 pm »
I stumbled across this... http://wwwhome.cs.utwente.nl/~ptdeboer/misc/mains.html which was quite interesting i.r.o. mains frequency derived clocks.

"discrete"? is that really what you meant?
 

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Re: Oscillator for discrete digital clock
« Reply #18 on: February 18, 2018, 06:42:45 pm »
Quote
.. Or some form of PWM to voltage conversion and comparator. Outcome again would be something more like a counter. I would assume.  ???   ...part count unknown.
Well, if you want an RC oscillator of that kind, you're going to have to go into really precision components. It would be interesting to see how accurate and stable you could make an RC (or similar) oscillator, if you used really high end parts, such as the LM399/LTZ1000, precision few ppm resistors, exotic comparators... the greatest problem would probably be a stable enough capacitor, though you could thermostat (and maintain precise humidity) it.
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Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #19 on: February 18, 2018, 07:02:14 pm »
I stumbled across this... http://wwwhome.cs.utwente.nl/~ptdeboer/misc/mains.html which was quite interesting i.r.o. mains frequency derived clocks.

"discrete"? is that really what you meant?
The mains synchronized clock would be the easiest and since it of course will be pretty power hungry contraption the mains power (and base clock pulse) would be there anyway. Interesting article, If they really do synchronize the grid to the reference time and frequency and not just to 50 Hz.

Just AC 12V or so transformer feed to the clock itself and then there is many easy ways to get the clock pulse from it. Crystal oscillator approach would be nice and allow use this as boat clock middle of the ocean. :P 

Discrete yes, discrete transistor / diode design.

I think the stable capacitor would be the most difficult part in the analog / digital hybrid. Let see this have been really a great help already to get my thoughts a bit more oriented.

I need to make my mind of I go for CMOS or TTL chip driven precision crystal or mains synchronized design, I think the D-flipflop divider from 32k crystal with discrete transistors screams a bit too much a lifetime project. Need to check my junk part box as there is all sort of old junk .. in hope of slow crystal. ::)

edit. some missing words added.
« Last Edit: February 18, 2018, 07:35:04 pm by Vtile »
 

Offline David Hess

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Re: Oscillator for discrete digital clock
« Reply #20 on: February 19, 2018, 12:24:06 am »
If Kalvin had not linked that I would have.  A series of injection locked oscillators can divide the 32,768 kHz crystal oscillator down to 1 Hz.  Since injection locked oscillators can divide by more than 2, fewer stages are required.
 

Offline NivagSwerdna

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Re: Oscillator for discrete digital clock
« Reply #21 on: February 19, 2018, 10:11:47 am »
Discrete yes, discrete transistor / diode design.
I wonder if you will ever finish.
 

Offline TomS_

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Re: Oscillator for discrete digital clock
« Reply #22 on: February 19, 2018, 10:30:54 am »
Discrete yes, discrete transistor / diode design.
I wonder if you will ever finish.

I built one using discrete NOR logic. I blogged about it, and all of the schematics are available on github: ornotblog.blogspot.com

Mine took about 5 months of reasonably intense work during evenings and over weekends to complete, and uses about 1500 transistors (roughly 2400 components in total).

You really do need to be committed...
 

Offline Zero999

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Re: Oscillator for discrete digital clock
« Reply #23 on: February 19, 2018, 11:25:34 am »
Looking for something like this?

https://upload.wikimedia.org/wikipedia/commons/6/6d/Transistor_Clock.jpg

No ICs included ;)
Yes... But with better implementation.  ;)

That one seems to take the base clock signal from the mains. Not too exited.

It should be quite easy to build a 32.768 kHz xtal oscillator and build 15 divide by two flip-flops giving 1 Hz.
... It would take ~250 parts if I'm not terribly mistaken..

..But this project doesn't make a much sense anyway.  :-DD
It's possible to build a divide by two counter with just two transistors.
 

Offline David Hess

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Re: Oscillator for discrete digital clock
« Reply #24 on: February 19, 2018, 11:50:43 am »
I like the idea of using discrete injection logic with the base resistors replaced with emitter resistors but it requires more transistors.  The bias voltage to the current sources can be adjusted for the lowest speed and power.
 


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