How read the frequency of crystal - Page 1
Forum section: electronics / beginners

author: Andbro
author_rank: Regular Contributor
timestamp: October 11, 2019, 04:13:49 pm
content: Hi,How measure the crystal frequency in circuit ?Thanks

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2019, 05:56:00 pm
content: 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.

author: magic
author_rank: Super Contributor
timestamp: October 11, 2019, 06:09:52 pm
content: Use a 100x probe to minimize the load10x 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.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2019, 06:11:50 pm
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: October 11, 2019, 06:17:43 pm
content: Or use a frequency counter, that's kind of what they're designed to do.

author: ataradov
author_rank: Super Contributor
timestamp: October 11, 2019, 06:20:02 pm
content: Quote from: james_s on October 11, 2019, 06:17:43 pmFrequency counters are not any better when it comes to input capacitance.

author: james_s
author_rank: Super Contributor
timestamp: October 11, 2019, 06:31:03 pm
content: 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.

author: magic
author_rank: Super Contributor
timestamp: October 11, 2019, 06:50:14 pm
content: 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 IIRCNot sure about the Hantek's absolute accuracy, but probably not worse than a $10 module tooAnd you still need some kind of probe which is going to load the circuit. Might as well use a scope and standard probe.

author: james_s
author_rank: Super Contributor
timestamp: October 11, 2019, 09:08:13 pm
content: 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.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 11, 2019, 09:13:11 pm
content: 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.

author: magic
author_rank: Super Contributor
timestamp: October 12, 2019, 07:44:25 am
content: Quote from: james_s on October 11, 2019, 09:08:13 pmPossibly not all of them, I only have that Hantek.Quote from: ejeffrey on October 11, 2019, 09:13:11 pmThis surely appliesAs 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.