HOWTO Determine Unknown XTAL Freq

What's wrong, Phyills, didn't your boyfreind show up last night? We know how cranky you get when you don't get....

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Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

"Michael A. Terrell, Psychotic, Autistic FREAK "

YOU can go a shove your pointy head up a dead donkey's backside where you normally hide it.

CUNT BRAIN !!

....... Phil

I think you just need to tell us (and Michael) how you really feel.

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Regardless of what you do you\'ll still need to measure the period of
the delay which, for an accurate determination of the crystal
frequency is going to take at least as much test equipment as
measuring the frequency of the crystal in an oscillator would.

Syphilis doesn't feel, she just flames.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Hm. Why am I getting a sudden urge to start reposting all that stuff about Dean Humphries catching his crackwhore wife blowing one of his friends?

What a very strange impulse to have after all these years.

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   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
  \\|/  \\|/              Perna condita delenda est
---^----^---------------------------------------------------------------

Do tell!

Well, I have something, admittedly not much, but it works for one of my junkbox crystals. See

jcomeau_ictx wrote in news: snipped-for-privacy@q75g2000hsh.googlegroups.com:

Build a crystal oscillator with an inverter (logic gate NOT) like this:

Usually best buffered by an extra gate if you're going to load it a bit:

74HC04 or 74HCT04 devices can work to over 100 MHz. NAND gates with inputs tied can be used as a NOT gate if spare. NAND gates are amongst the cheapest IC's ever.

innews: snipped-for-privacy@q75g2000hsh.googlegroups.com:

this:

bit:

Nice! Those circuits are about my speed. I'm headed out of town for a week, but plan to update my page when I get back. Thanks -- jc

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Not to rain on your parade, but the difference between 7.15625 and
7.19780 is 0.04155, which is an error of 0.58%, a _huge_ error in
the land of crystals. ;)

No, that doesn't rain on my parade, as the calculation was based on eyeballing a moving LED display. If I wanted accuracy I would have rewritten the program to calculate the result itself with a stable timebase, and displayed it in binary on the LEDs. This was just a proof-of-concept, and since I had only one crystal that worked, it doesn't really qualify as that, but the amount of accuracy does make it seem a plausible approach.

jcomeau_ictx wrote in news: snipped-for-privacy@n76g2000hsh.googlegroups.com:

Bear in mind that while logarithms involve precision that justifies 12 bit ADC/Process/DAC work, getting accurate voltage conversions from frequency is far less demanding. It's linear, and you can get a 1 Hz to 1 MHz range within the range of 20µV to 20V, a fairly easy task with one of various cheap freq/volt converter IC's and a cheap op-amp like an LF411, let alone something more exotic. You can make switched ranges if needing more, or sample a pulse train digitally. Either way, you can start with one of those circuits I linked to from my other post, the one with the hex inverters in it. Why settle for an estimate when you can get high precision for less than most kids would consider as adequate pocket money?

If you can find a freq/volt IC that has connections for a crystal to be added, and a variable gain on the output, you could do everything with that IC and a voltmeter. I don't know if such a singular IC exists, but if I had a lot of crystals to test, I'd be looking for one.

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The insurmountable problem I see with your approach is that no
matter what you do you can\'t use the µC\'s time base to determine its
own frequency since you\'ll either have to have a reference time base
running independently from your µC time base or, knowing the
frequency and accuracy of your µC time base, use it as the
referenced against which to measure the period/frequency of the
crystal being tested in a _separate_ oscillator. In either case what
you\'ll have built is a conventional frequency or period counter.

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The circuits you\'re referring to are merely oscillators, and will do
nothing except get the crystal to oscillate so that its frequency
can be measured.

As far as I know there are _no_ frequency-to-voltage converters with
the accuracy required to measure frequency with anything coming even
close to the crystal\'s own accuracy, and if there are they won\'t be
cheap.

I could be wrong, of course, so if you can find one and post which
one it is, I\'ll gladly admit to being wrong.

snipped-for-privacy@n76g2000hsh.googlegroups.com:

se

That looks like an interesting approach. I'd need a better VOM than I have now, though, to be able to take advantage of the high precision. And it seems most kids nowadays have more pocket money that I do.

Yes, that's a problem for sure. I wonder how accurate is the 60 Hz from the power company? A quick websearch didn't come up with anything. If it were reliable to a few PPM that might work as a timebase. And IIRC the PIC devices have protective circuitry on the I/ O pins so all you need is a current-limiting resistor, say ten megohms.

Right. One that anyone with a PIC device could make in a few minutes when needed, and repurpose for other uses afterwards.

In any case, I probably won't pursue this any more unless I have need for it myself. If the OP really gives a damn about his crystals, there's enough useful info in this thread now.

John Fields wrote in news: snipped-for-privacy@4ax.com:

I never said otherwise.

That's true too, but it would still be better than the kind of error you showed existed in the other method. Not over the entire range, perhaps, but it should be a reasonable match for the 0.5% typical of many multimeters.

My emphasis was on cheap, and easy, and how you can make a significant improvement on accuracy this way.

jcomeau_ictx wrote in news: snipped-for-privacy@l77g2000hsb.googlegroups.com:

Trust me... don't go there. >:)