[time-nuts] Re: Crystal oscillator for a begginer

[Chris Caudle]

On Wed, January 5, 2022 5:01 pm, Adam Space wrote:
> My knowledge of hardware is pretty weak

How would you quantify "pretty weak?"  You could connect up the components
correctly, but you could not design a circuit from scratch?  Or you are
worried you will let the smoke out the first project you start?

> But I am confused on how I could exactly use this [crystal oscillator]

A "canned" crystal oscillator is a quartz crystal and circuitry together
in a package that provides an oscillating electrical output when connected
to power.
For the specific device you mentioned, you connect it to a 5V power
supply, and the output will vary between 0.5V and 4.5V 10 million times
per second.

> if I have a crystal oscillator going, how could I compare it or adjust
it to
> other clocks on my network, or to UTC for example?

First, a crystal oscillator has no concept of time, so discussion of
adjusting to UTC does not make sense in that context.  The output swings
low to high to low and that is it.

If you want a clock, you need something which oscillates (quartz
oscillator, atomic states of cesium atoms, pendulum, etc.) and you need a
mechanism to count and display the oscillations.
So to make a clock with your 10MHz quartz oscillator you would need an
electronic circuit compatible with the electrical levels of that
oscillator, which includes a counter that can increment at that rate, and
probably circuitry to divide down the 10 million cycles per second to more
usable rates (1 cycle per second, 1 cycle per hour, etc.).  Unless you are
satisfied just knowing that the circuit is busy counting cycles, you
probably also want a way to either display the current count, or output
the count in some electrical format for use elsewhere.
Unless your counter is completely self referenced, you will probably also
want a way to set the count to a predetermined count right after it powers
on so that it matches your other clocks.

> Or to take another example, suppose I have a few crystal oscillators like
> the one above. Is there a way I could compare them to each other, or log
> the offsets from each other, and so on?

Yes, and depending on how quickly you need to know, how precisely you need
to know, and over what time periods you need to know (or alternately what
frequency offset if viewing in frequency domain rather than time domain)
there are quite a few ways.
The most basic is to use a frequency counter instrument with a time base
much better than the device you are trying to measure and count how many
cycles occur over a particular time period.  For example, you could could
the transitions on the output of your oscillator for 1 second, and display
the count.  You expect it to be around 10 million, but oscillators vary in
accuracy as built, and drift with time, temperature, power supply
variations, etc.  Unless your counter can generate the start and stop
counting signals very accurately 1 second apart, you can't be sure how
much of the difference between the actual count and 10 million is due to
the device you are testing, and how much is due to inaccuracy in the
measuring device.
For the oscillator you mentioned the problem is not very difficult, most
good quality test equipment has much better accuracy oscillators
internally, but as you attempt to measure higher and higher quality
oscillators it becomes more challenging making the test equipment good
enough to be sure you are actually measuring your device, and not just
displaying the limits of the test equipment.

> Ultimately, it would be nice to
> compare the frequency and time offsets to a reference source that is
> accurate long-term, like my GPS hat Raspberry Pi.

You have the right idea, although a Rasberry Pi is probably not the ideal
tool for that job.
There are different tools needed as well for comparing how far apart two
devices have drifted over the course of a day, week, or month compared to
what you would use to determine how much the frequency varies second to
second, or millisecond to millisecond, or how the time period between any
two positive going edges of your 10MHz signal compares to the time between
any other two consecutive edges.

> Any ideas, suggestions, or clarifications are welcome. Additionally, if
> anyone knows of any guides (either text, video, or whatever), that would
> be great too.

You could start with this as a breezy introduction:
http://leapsecond.com/ten/

This will keep you busy for a long time:
http://www.resonal.com/Downloads/John%20R.%20Vig%20-%20tutorial%20on%20Quartz%20Crystals%20and%20Oscillators.pdf

(apologies if my mail editor mangles that link, hopefully you can put it
back together successfully if that is the case).

-- 
Chris Caudle