# Check frequency

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Hi all

I have a requirement to exactly adjust the frequency of a microcontroller system (8051) that works with the 32768 Hz watch crystal.

I am not an electronics engineer but a hobby type. I will thank you to please let me know how the system can made to work exactly at the above frequency. Trimmers are provided. my understanding is that you need an oscilloscope to do this. In that case what kind should I go for? Os is there a simpler methods?

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Thank you very much for your time

ClueLess```
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For this application an oscilloscope will be useless and you should use
a frequency counter.```
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Define 'exactly'. You will need a very accurate standard to compare your oscillator with, and the crystal won't allow much alteration of frequency, regardless of 'trimmers'.

An oscilloscope and Lissajous techniques can do part of the job, but frequency accuracy can be a challenging task; some clocks reach ten significant figures, it matters a LOT what your accuracy requirement is.

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"John Fields"

** Shame how even the cheapest DSOs have built in frequency measurement to 5 decimal places.

... Phil

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"ClueLess

** To get the frequency exact, you need resolution better than 1 Hz - one way is to use a frequency counter that can be set to count for 10 seconds - giving you 327 thousand odd counts on the display.

Picking up a signal voltage from the crystal without disturbing it is a problem too - most counters would stop the oscillations if directly connected.

Time for a Reality check:

Just how " exact " do you really need it ??

A watch crystal will be within about 30ppm (or 1 Hz ) with no adjustment.

To get better accuracy, you will need at a dual trace scope and a quartz clock that keeps good time.

Dunno why you are playing with uPs when you have no scope.

.... Phil

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Set the device up to count cycles between input pulses and feed it the

1 Hz pulse train from a GPS, trim until you get close enough to 32768
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"Jasen Betts"

** Sheep shagger extraordinaire.

** The crystal will be 32.768 kHz out of the box.

Idiot.

.... Phil

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Shame how analog scopes, which is (since he didn't say "DSO") what he
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Actually, out of the box it'll be a little high.```
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I don't think so.

If you've got a 32768 Hz crystal in an oscillator and you want to```
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Then they run in circles chasing it. :)

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Offworld checks no longer accepted!```
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"John Fields" "Phil Allison"

** Pedantic bollocks.

The OP is a novice and has no scope at present.

A low price ( ie \$300) DSO is just what he should get.

.... Phil

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"John Fields" "Phil Allison"

** You don't think straight at all.

Never have.

** Meaningless drivel.

..... Phil

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Got any suggestions as to which one?

JF```
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Just because you don't recognize it as straight thinking doesn't mean it
isn't.```
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Thank you very much got your very detailed suggestions, I will look for a frequency counter and try as you said.

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Thanks again
ClueLess```
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"ClueLess" John Fields

** Don't do that.

That advice is crap and will not work.

Get a scope with two traces.

But first tell US what sort of accuracy you NEED and why !!

..... Phil

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"John Fields" "Phil Allison"

** Fraid it is just more of your crazed, autistic crapology.

** Fraid it is just more of your crazed, autistic crapology.

...... Phil

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Er... no, that's not right. If you have a suitable reference frequency source, you can watch the pretty Lissajous figure on an X/Y oscilloscope (no dual channel, no counter) and if it goes through a cycle in 100 seconds, with 0.1 second stopwatch accuracy, you've just made a frequency measurement with .001 Hz accuracy. For your

32 kHz crystal, that's a second per year kind of accuracy.

A frequency counter is a convenient and quick solution, but it is NOT required nor is it superior in accuracy.

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"whit3rd" ClueLess John Fields

Er... no, that's not right. If you have a suitable reference frequency source, you can watch the pretty Lissajous figure on an X/Y oscilloscope (no dual channel, no counter) and if it goes through a cycle in 100 seconds, with 0.1 second stopwatch accuracy, you've just made a frequency measurement with .001 Hz accuracy. For your

32 kHz crystal, that's a second per year kind of accuracy.

A frequency counter is a convenient and quick solution, but it is NOT required nor is it superior in accuracy.

** Ask JF where the OP can get an affordable counter that reads a frequency in Hz to seven decimal places - as in his " 32768.XXXXXXX Hz ".

His magic 10 turn crystal PU loop need to be patented too.

...... Phil

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