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.
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?
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
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.
... It would take ~250 parts if I'm not terribly mistaken..
..But this project doesn't make a much sense anyway.
Using 0201 size passives and SOT-723 transistors it might be surprisingly small, though. Wristwatch made using discrete components!
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
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.
... 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.
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.
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.
... 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.
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.
.. 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.
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.
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.
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.
Discrete yes, discrete transistor / diode design.
I wonder if you will ever finish.
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...
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.