Author Topic: How read the frequency of crystal  (Read 2145 times)

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Offline AndbroTopic starter

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How read the frequency of crystal
« on: October 11, 2019, 04:13:49 pm »
Hi,

How measure the crystal frequency in circuit ?

Thanks
 

Online ataradov

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Re: How read the frequency of crystal
« Reply #1 on: October 11, 2019, 05:56:00 pm »
If it is a working oscillator circuit, then put an oscilloscope probe on one of the pins and observe the waveform. Use 10X probe to minimize the load.
Alex
 

Offline magic

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Re: How read the frequency of crystal
« Reply #2 on: October 11, 2019, 06:09:52 pm »
Use a 100x probe to minimize the load >:D
10x ones have input capacitance similar to typical crystal capacitors.

That being said, 10x will work too but frequency will change some fraction of a percent when the probe is connected. Ideally, you would try to measure the resulting clock rate of the whole IC rather than the oscillator directly.
« Last Edit: October 11, 2019, 06:12:33 pm by magic »
 

Online ataradov

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Re: How read the frequency of crystal
« Reply #3 on: October 11, 2019, 06:11:50 pm »
Well, in practice I never had a problem with 10x.

It also depends on what you mean by "read". If you just need to figure out if it is 8 MHz or 16 MHz crystal, then 10X is plenty.

If you want to actually determine the frequency, your setup may get rather complicated depending on the required accuracy.
Alex
 

Offline james_s

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Re: How read the frequency of crystal
« Reply #4 on: October 11, 2019, 06:17:43 pm »
Or use a frequency counter, that's kind of what they're designed to do.
 

Online ataradov

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Re: How read the frequency of crystal
« Reply #5 on: October 11, 2019, 06:20:02 pm »
Or use a frequency counter, that's kind of what they're designed to do.
Frequency counters are not any better when it comes to input capacitance.
Alex
 

Offline james_s

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Re: How read the frequency of crystal
« Reply #6 on: October 11, 2019, 06:31:03 pm »
No but they're typically more precise, and less expensive than an oscilloscope if you don't already have a scope. I only listed it as another option.

A while back I picked up a <$10 frequency counter module from China out of curiosity and found that it's actually quite good.
 

Offline magic

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Re: How read the frequency of crystal
« Reply #7 on: October 11, 2019, 06:50:14 pm »
You mean that "High Sensitivity 1Hz-50MHz Frequency Meter Counter Measurement Tester Module 7V-9V 50mA DIY Kit"?
That's 5 digits resolution, my Hantek scope has 5 or 6 IIRC :P
Not sure about the Hantek's absolute accuracy, but probably not worse than a $10 module too ;)

And you still need some kind of probe which is going to load the circuit. Might as well use a scope and standard probe.
 

Offline james_s

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Re: How read the frequency of crystal
« Reply #8 on: October 11, 2019, 09:08:13 pm »
I don't recall if that's what it is or not, I just remember I bought it out of curiosity and ended up being surprised. Didn't realize scopes were giving that much frequency resolution these days, mine only show frequency to 2-3 decimal places. My real benchtop frequency counter is far more precise.

Anyway like I said, it's just an option, use what you've got.
 

Online ejeffrey

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Re: How read the frequency of crystal
« Reply #9 on: October 11, 2019, 09:13:11 pm »
To really minimize loading use a near field probe with a spectrum analyzer. It all depends on what you want to do and what equipment you already have.
 
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Offline magic

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Re: How read the frequency of crystal
« Reply #10 on: October 12, 2019, 07:44:25 am »
Didn't realize scopes were giving that much frequency resolution these days, mine only show frequency to 2-3 decimal places.
Possibly not all of them, I only have that Hantek.
It all depends on what you want to do and what equipment you already have.
This surely applies :-+

As for the Hantek, its "measurements" panel also only shows frequency to 2-3 decimal digits, but there is an additional trigger event counter which is always visible and provides several digits of resolution at high frequencies. IIRC its gating interval is 1s and it doesn't do reciprocal counting, but that's good enough for MHz crystals.
 


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