Re: 32Hz stable discrete square wave oscillator, how to?

A tuning fork oscillator is electromechanical, it's just like a musical tuning fork but has a coil and circuit beside it to amplify and sustain the vibration. They can be very stable but at 32Hz I suspect the fork would be quite big to fabricate and difficult to temperature stabilize.

Brian.

Mechanical resonance is just a matter of mass and stiffness.

Only effect of temperature would be thermal expansion, and invar is a special metal alloy SPECIFICALLY formulated to have zero thermal expansion.
It is used for all kinds of very high precision mechanical applications.

Its rather like scaling up a quartz crystal oscillator to work directly at only 32 Hz.
And it should be just as stable as a quartz oscillator, perhaps even better.
Pretty fringe engineering, but entirely possible.

Its already been done back in about the 1940's.
Here are some pictures of an invar 60Hz tuning fork frequency reference.
Hardly practical these days, but definitely possible.
http://leapsecond.com/museum/gr815b/

I know that it is not discrete, but will 32Hz out of the PC sound blaster be stable in frequency enough?
What short of stability should I expect from a software synthesizer program?

It should be very stable but might be difficult to utilize without picking up traces of noise from the PSU and other digital circuits. My other concern is extracting the signal without it passing through any AC coupled stages on the sound card. At such low frequency you might see significant distortion to a square wave.

Brian.

there are a few sound cards that are DC coupled..but not too many.

or you could go into the card and jumper over the DC blocking cap at the DAC output to make it DC Coupled, or replace it with a larger value capacitor.

http://forum.arcadecontrols.com/inde...topic=135230.0

I don't see how a soundcard frequency derived from an uncalibrated cheap xtal could be anywhere near your "better than TCXO" requirement.

You find arbitray specifications along the thread, I gave up to think about it. Hopefully neazoi knows his actual requirements.

Regarding sound card output, it's easy to convert the signal to a square wave, worst case by using a comparator. So I don't see an issue in this regard.

I started the thread as "discrete" but since I see from the answers that it is not so easy, I start to investigate other chip-free ways as well. Well the PC is chip-full, byt anyway.

Square wave can be made with a diode clipper too I think. More important is the frequency stability. I cannot tell you the requirement on this because I do not know what will be the effect of any amount of instability on this circuit http://www.hanssummers.com/huffpuff/...ist/2chip.html in which the oscillator is to be used.

Holy cow!

How can you think that 32Hz audio from PC, with all its jitter, multiplied a million times to MHz range, would be useful to stabilize a VFO ?

Is it multiplied? The flip flop requires a 32Hz signal and that is derived from a divided oscillator in the euthor's schematic. Am I losing something here?

Hi,

a simple AVR or PIC with xtal and hardware generated square wave will be much more precise than a soundcard output.
Good audio equipment has low jitter, but if you generate sine (or audible waveform) from a cheap soundcard and then use amplifiers and/or comaprators to form a square wave..... i don′t think this is a good way.

In the link of post#29 they use 32000Hz or 32768 Hz, you talk about 32Hz. You are sure you need 32Hz?

Klaus

Thanks Klaus.
Not exactly, the frequency is not too important, it could be even 30 or 25 or 20... It is the stability that is more important.
From the posts, it seems that there is no good discrete way to do this, you have to use an IC or a tuning fork.

Hi,

the frequency is not that important.

Do you need:
* low (cycle by cycle) clock jitter, or
* low frequency drift (like thermal...)

can you give max values on that?

Klaus

Yes, it is multiplied. Your "huff puff" function is similar to a PLL design, where fRF = n * fREF.
Any instability in the reference will be multiplied by factor n.

You don't see the multiplier? From a system perspective, dividing the RF frequency is the exact same thing as multiplying the reference.

http://www.eham.net/reviews/detail/8437

It isn't quite the same as a PLL, the idea behind 'huff n puff' is it locks to increments of the reference rather than multiples of it. If I remember back to the original design proposal in Radcom magazine in the early 70's it used a 1MHz XTAL reference and had a 1 second time constant in the VCO filter (1M Ohm and 1uF I think). The stability is related to the reference but only in so far as an error in one may be duplicated in the other. For example if 32Hz was the reference producing 1MHz, 32.1Hz would produce 0.1Hz error in the 1MHZ, in other words the error is not multiplied.

Brian.

A limitation with all these circuits is that they lock in 32Hz increments o/k, but if the frequency drift is much greater they "jump" and lock onto the next 32 Hz increment in frequency.
So it will cure a very slow frequency wander, but if the frequency drift is considerable, it will jump instead of drift.

Do you have mains AC in the vicinity? Here's an idea. Tap into that. It will give you stable 50 or 60 Hz. Then divide by 2 through a flip flop.

You probably do not need to connect directly to mains. It should be possible to pick up mains hum in appliances several feet away. The right length, or shape, of antenna might help. Amplify the signal. Divide by 2 or 3 as you desire.

Actually not necessarily true in the case of 'Huff n Puff', the lock range depends on the available control voltage range and it's tuning coefficient. In fact the biggest problem with this kind of control mechanism is difficulty changing the frequency and re-locking again. I note the kit mentioned a few posts back uses a variable time constant to allow rapid tuning with the stabilizer catching up only after the tuning stops.

Brian.