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

On Dec 16, 6:21=A0am, 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.

"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

"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

On 2009-12-16, ClueLess <c...@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

"Jasen Betts" <j...@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

On Thu, 17 Dec 2009 12:58:38 +1100, "Phil Allison" <p...@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 

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

>
>"Jasen Betts" <j...@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 

On Thu, 17 Dec 2009 13:26:31 +1100, "Phil Allison" <p...@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... µs  
---

> -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