Author Topic: Oscillator for discrete digital clock  (Read 8683 times)

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Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #50 on: February 19, 2018, 08:29:07 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
That is/were my original plan to use diode gates and some transistors for buffers and inversions.
 

Offline Zero999

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Re: Oscillator for discrete digital clock
« Reply #51 on: February 19, 2018, 09:16:57 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
No, it's much simpler than that. As I said in another post, the basic divide by two stage only needs two transistors. Here's another schematic and link to a tutorial.

https://www.electronics-tutorials.ws/waveforms/bistable.html
 

Offline VtileTopic starter

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Re: Oscillator for discrete digital clock
« Reply #52 on: February 19, 2018, 09:21:34 pm »
14*15 = 210 parts.  ;)
 

Offline Zero999

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Re: Oscillator for discrete digital clock
« Reply #53 on: February 19, 2018, 09:39:32 pm »
14*15 = 210 parts.  ;)
Where do you get 14*15 from, or is a joke I don't get?

Each flip-flop divides by two. If you have a 32768Hz oscillator, then you need to divide by 32768 or 215 to get 1Hz. If you put 15 divide by two counters in series, you'll get a divide by 32768 counter. 15 flip-flop and using the above design, would only require 30 transistors.
 

Offline glarsson

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Re: Oscillator for discrete digital clock
« Reply #54 on: February 19, 2018, 09:47:52 pm »
14 parts including two transistors.
15 * 14 is no joke.
 

Offline Zero999

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Re: Oscillator for discrete digital clock
« Reply #55 on: February 19, 2018, 10:48:21 pm »
14 parts including two transistors.
15 * 14 is no joke.
Of course. I was just counting the transistors. Silly me.  :-DD

How about this circuit instead?

Use a dual diode for D11 & D12 and D10 & D13 and now it's only 10 parts, or would that count as an IC which is cheating?


http://ch00ftech.com/2012/07/10/transistor-clock-part-2-prescaler/
« Last Edit: February 19, 2018, 10:58:03 pm by Hero999 »
 
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Offline duak

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Re: Oscillator for discrete digital clock
« Reply #56 on: February 20, 2018, 03:30:30 am »
Look up "astable multivibrator frequency divider".  There is at least one patent describing it.  This circuit will give a greater divide ratio per stage than a purely digital divider.  The principle is that each stage is an oscillator tuned to have a free running frequency just a bit lower than the desired frequency.  Each stage will then lock to an exact sub-multiple of the frequency applied to its trigger input.

I first ran across this concept in an article in Scientic American from the 50's where vacuum tubes were used for the active devices.

You might also want to look at some digital instruments built in the 50's & early 60's before integrated circuits.  hp built counters with really efficient designs

Cheers,
 
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Online BrianHG

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Re: Oscillator for discrete digital clock
« Reply #57 on: February 20, 2018, 04:53:41 am »
Well, as others have cited, just like you can have a third overtone & 5th overtone crystals, which are crystals at 1/3rd, or 1/5th their written value with a LC tuned oscillator just running at 3x or 5x speed, it might be possible to go in the opposite direction.  Get a 32.768 Khz crystal, connect it to an LC oscillator tuned at some odd number dividend, the further away, the more difficult to retain lock, and it should work.  This means you basically use a 1 transistor LC oscillator tuned to, example 1/9th 32.768k = 3.640888889 Khz.  Then use that oscillator as a reference for the next stage 1 transistor oscillator to divide by 9 again = 404.5432099 hz, then /9 again = 44.94924554 hz.  That's 3 transistors to go from 32k to 44.949hz.  But, you also need 3 ferrite tunable inductors or 3 varicaps which may drift with temperature and time.

A divide by 3 or 5  per stage would be more tolerant.  In theory, maybe even a divide by 15 or even bigger may work.  At that level, I would breadboard a 1 transistor fundamental 32Khz, with it's output going through a 5pf to 100pf feeding the base of a second 1 transistor LC oscillator tuned to something like 1/101 the frequency and fiddle around with the inductor's tuning just to see if there is any harmonic locking.  It will stand out on a scope as you adjust the frequency (ie tune the inductor), there will be zones where the frequency seems to snap to a fixed value.  If you have a REAL frequency counter, it's reading will stabilize in these zones while anywhere else, the frequency will be unstable or drift.  This would give you a 32Khz / 101 with only 2 transistors... Or try smaller divisions.  A smaller divide by 3 or 5 would snap/lock very hard.

This should be bread-board-able with a couple of 2N3904, 1 watch crystal, some caps, resistors and a TOKO 7 style 2mh adjustable inductor.  Maybe buffer the output with a third 2N3904 to isolate your scope probe's capacitance, and as a LPF to remove any 32Khz from the source, as tuning to a /101 will be really touchy.
« Last Edit: February 20, 2018, 05:55:16 am by BrianHG »
 
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