Check frequency

[ClueLess]

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?

--
Thank you very much for your time

ClueLess

 

[John Fields]

On Wed, 16 Dec 2009 19:51:26 +0530, ClueLess
<clueless@wilderness.org.invalid> wrote:

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?

---
For this application an oscilloscope will be useless and you should use
a frequency counter.

In order to keep from loading the crystal, what I'd do would be to wind
an air-cored coil, about an inch in diameter and 10 - 20 turns wide with
its ends soldered to a BNC female connector. Then connect it to one end
of a piece of coaxial cable terminated in BNC males and connect the
other end of the cable to the counter's frequency input.

Set the counter's trigger level control close to zero and place the coil
in the vicinity of the crystal. You'll probably have to fiddle with the
coil placement and the trigger level control to get a reading, but when
you do then you'll be able to trim the crystal to 32768.XXXXXXX Hz
depending on the accuracy of the counter. Once you get it set, move the
coil around to make sure that it's not interacting with the crystal by
observing that the reading doesn't change, and you'll be set.

Another way would be to write a little routine which would force an IO
high for a known period of time with a clock frequency of 32768 Hz and
then to measure the period of the pulse with a counter and trim the
oscillator until the period was precisely what it should be.

For example, if the period of the pulse was supposed to be 100 clock
cycles long, including all of the instruction execution times, then the
width of the output pulse would be:

1
T = --------- * 100 = 3.051757E-3 seconds
32768Hz

The advantage of this method would be not having to screw around with
hardware, while the disadvantage, of course, would be keeping track of
all those instruction cycles (only once, though...).

JF

 

[whit3rd]

On Dec 16, 6:21 am, ClueLess <cluel...@wilderness.org.invalid> wrote:

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.

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.

 

[Phil Allison]

"John Fields"

For this application an oscilloscope will be useless and you should use
a frequency counter.

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


.... Phil

 

[Phil Allison]

"ClueLess

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?

** 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

 

[Jasen Betts]

On 2009-12-16, ClueLess <clueless@wilderness.org.invalid> wrote:

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?

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

 

[Phil Allison]

"Jasen Betts" <jasen@xnet.co.nz>

** Sheep shagger extraordinaire.

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

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

Idiot.



..... Phil

 

[John Fields]

On Thu, 17 Dec 2009 12:58:38 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"John Fields"

For this application an oscilloscope will be useless and you should use
a frequency counter.


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

---
Shame how analog scopes, which is (since he didn't say "DSO") what he
was talking about, don't.

JF

 

[John Fields]

On Thu, 17 Dec 2009 19:21:12 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"Jasen Betts" <jasen@xnet.co.nz

** Sheep shagger extraordinaire.


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


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

---
Actually, out of the box it'll be a little high.
---

Idiot.

---
A dog smells his own farts first, yes?

JF

 

[John Fields]

On Thu, 17 Dec 2009 13:26:31 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"ClueLess

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?


** To get the frequency exact, you need resolution better than 1 Hz

---
I don't think so.

If you've got a 32768 Hz crystal in an oscillator and you want to
measure the output frequency to an accuracy of, say, +/- one part in
32768, then if you use a 1 second timebase to accumulate cycles it has
to have a resolution of +/- 30.51757... ľs
---

-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.

---
True.
---

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

---
Using a 10 megohm scope probe to connect the counter to the driven side
of the crystal, IME, won't stop it, but it will pull it.
---

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


JF

 

[Michael A. Terrell]

John Fields wrote:

Phil Allison wrote:

Idiot.

A dog smells his own farts first, yes?

Then they run in circles chasing it.


--
Offworld checks no longer accepted!

 

[Phil Allison]

"John Fields"
"Phil Allison"

For this application an oscilloscope will be useless and you should use
a frequency counter.


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


---
Shame how analog scopes, which is (since he didn't say "DSO")

** 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

 

[Phil Allison]

"John Fields"
"Phil Allison"

** To get the frequency exact, you need resolution better than 1 Hz

---
I don't think so.

** You don't think straight at all.

Never have.

If you've got a 32768 Hz crystal in an oscillator and you want to
measure the output frequency to an accuracy of, say, +/- one part in
32768, then if you use a 1 second timebase to accumulate cycles it has
to have a resolution of +/- 30.51757... ľs

** Meaningless drivel.



...... Phil

 

[John Fields]

On Fri, 18 Dec 2009 09:41:28 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"John Fields"
"Phil Allison"


For this application an oscilloscope will be useless and you should use
a frequency counter.


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


---
Shame how analog scopes, which is (since he didn't say "DSO")


** 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.

---
Got any suggestions as to which one?

JF

 

[John Fields]

On Fri, 18 Dec 2009 09:44:14 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"John Fields"
"Phil Allison"


** To get the frequency exact, you need resolution better than 1 Hz

---
I don't think so.

** You don't think straight at all.

Never have.

---
Just because you don't recognize it as straight thinking doesn't mean it
isn't.

For example, if you think that the '8' in 32768 Hz represents 1 Hz, as
you seem to indicate, I suggest you consider that it represents 1 part
in 32768 Hz, which is ~ 30.5ľs, not 1s/1Hz.
---

If you've got a 32768 Hz crystal in an oscillator and you want to
measure the output frequency to an accuracy of, say, +/- one part in
32768, then if you use a 1 second timebase to accumulate cycles it has
to have a resolution of +/- 30.51757... ľs

** Meaningless drivel.

---
How would you state it then?

JF

 

[ClueLess]

On Wed, 16 Dec 2009 09:25:28 -0600, John Fields
<jfields@austininstruments.com> wrote:

For this application an oscilloscope will be useless and you should use
a frequency counter.

Thank you very much got your very detailed suggestions, I will look
for a frequency counter and try as you said.

--
Thanks again
ClueLess

 

[Phil Allison]

"ClueLess"
John Fields

For this application an oscilloscope will be useless and you should use
a frequency counter.

Thank you very much got your very detailed suggestions, I will look
for a frequency counter and try as you said.

** 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

 

[Phil Allison]

"John Fields"
"Phil Allison"

** To get the frequency exact, you need resolution better than 1 Hz

I don't think so.

** You don't think straight at all.

Never have.

Just because you don't recognize it as straight thinking doesn't mean it
isn't.

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

For example, if you think that the '8' in 32768 Hz represents 1 Hz, as
you seem to indicate, I suggest you consider that it represents 1 part
in 32768 Hz, which is ~ 30.5ľs, not 1s/1Hz.

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



....... Phil

 

[whit3rd]

On Dec 17, 6:01 pm, ClueLess <cluel...@wilderness.org.invalid> wrote:

On Wed, 16 Dec 2009 09:25:28 -0600, John Fields

jfie...@austininstruments.com> wrote:
For this application an oscilloscope will be useless and you should use
a frequency counter.

Thank you very much got your very detailed suggestions, I will look
for a frequency counter and try as you said.

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.

 

[Phil Allison]

"whit3rd"
ClueLess
John Fields

For this application an oscilloscope will be useless and you
should use a frequency counter.

Thank you very much got your very detailed suggestions, I will
look for a frequency counter and try as you said.

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