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'50 MHz Freq Meter'
1998\08\09@052309 by Ari Wahyudi

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I read about 50MHZ Freqmeter developed bySimone Benvenuti and Andrea
Geniola using PIC16C84.
I just don't understand how it works. HOw the PIC can measure such that
high frequency, since it only use 4MHz clock frequency..
Anybody can explain?

Thank's for advance.

-ari-

1998\08\09@084816 by Nigel Goodwin

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In message <Pine.BSF.3.96.980809160835.3052B-
spam_OUT100000TakeThisOuTspamelka93.ee.itb.ac.id>, Ari Wahyudi <.....ariKILLspamspam@spam@ELKA93.EE.ITB.AC.ID>
writes
>I read about 50MHZ Freqmeter developed bySimone Benvenuti and Andrea
>Geniola using PIC16C84.
>I just don't understand how it works. HOw the PIC can measure such that
>high frequency, since it only use 4MHz clock frequency..
>Anybody can explain?

It uses the built-in prescaler, this is effectively a 16 bit hardware
counter which can be clocked by the incoming frequency. The counter can
be read (by devious means!) after a predetermined time interval, and the
frequency calculated.
--

Nigel.

       /--------------------------------------------------------------\
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       | Lower Pilsley   | Web Page : http://www.lpilsley.demon.co.uk |
       | Chesterfield    |                                            |
       | England         |                                            |
       \--------------------------------------------------------------/

1998\08\09@091357 by Ari Wahyudi

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On Sun, 9 Aug 1998, Nigel Goodwin wrote:
> >I read about 50MHZ Freqmeter developed bySimone Benvenuti and Andrea
> >Geniola using PIC16C84.
> >I just don't understand how it works. HOw the PIC can measure such that
> >high frequency, since it only use 4MHz clock frequency..
> >Anybody can explain?
>
> It uses the built-in prescaler, this is effectively a 16 bit hardware
> counter which can be clocked by the incoming frequency. The counter can
> be read (by devious means!) after a predetermined time interval, and the
> frequency calculated.

But  PIC16C84 datasheet/manual mention that external clock is
synchronized with Osc Clock, and it is necesary for TOCKI to high at
least 2Tosc and low for at least 2Tosc..

-ari-
still confusing

1998\08\09@102936 by Nagendra, VU2CLN

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check out www.man.ac.uk/~mbhstdj/files/counter.zip
It's a Frequency counter designed on 16F84 with very user friendly
description of source code





Virtually yours,
   Nagendra


Bye,73's
*---------------------------------------------------------------------------
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|Celebrating 50 years Of Indian Independence,                           |
|Proud to be Indian ,VU2CLN
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If speed scares you, try Windows...
Multitasking: You can crash several programs all at once. No waiting!

1998\08\09@175130 by Leon Heller

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In message <Pine.BSF.3.96.980809200104.3427A-
EraseME100000spam_OUTspamTakeThisOuTelka93.ee.itb.ac.id>, Ari Wahyudi <arispamspam_OUTELKA93.EE.ITB.AC.ID>
writes
>On Sun, 9 Aug 1998, Nigel Goodwin wrote:
>> >I read about 50MHZ Freqmeter developed bySimone Benvenuti and Andrea
>> >Geniola using PIC16C84.
>> >I just don't understand how it works. HOw the PIC can measure such that
>> >high frequency, since it only use 4MHz clock frequency..
>> >Anybody can explain?
>>
>> It uses the built-in prescaler, this is effectively a 16 bit hardware
>> counter which can be clocked by the incoming frequency. The counter can
>> be read (by devious means!) after a predetermined time interval, and the
>> frequency calculated.
>
>But  PIC16C84 datasheet/manual mention that external clock is
>synchronized with Osc Clock, and it is necesary for TOCKI to high at
>least 2Tosc and low for at least 2Tosc..

That's for input to TMR0, not the prescaler.

Leon
--
Leon Heller: @spam@leonKILLspamspamlfheller.demon.co.uk http://www.lfheller.demon.co.uk
Amateur Radio Callsign G1HSM    Tel: +44 (0) 118 947 1424
See http://www.lfheller.demon.co.uk/dds.htm for details of a simple AD9850
DDS system. See " "/diy_dsp.htm for a simple DIY DSP ADSP-2104 system.

1998\08\09@192522 by Don

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It does seem well documented. I downloaded it, but havent built it. Did
you? The only thing I dont understand is how to calculate the three time
loops (T1 T2 T3) for a given crystal frequency. Or, do you just make
them up and any set of values is fine if it satisfies the total timing
formula that is given? Also, I guess the same question goes for the nops
for fine tuning (X, Y, and Z). It would be nice to be sure. That way you
could make an estimate, then build the counter, and compare it against a
reference counter, then recalculate the fine tuning and hit perfect
calibration by only making two chip burns.
Don


Nagendra, VU2CLN wrote:
{Quote hidden}

1998\08\09@201124 by Regulus Berdin

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Hi all,

This is done by having TMR0 as the input and shorting one I/O to it.
Adjust the prescaler to divide by 256, this will hold the lower 8
bit of your data.

On your program, for example you want a 1 Hz resolution, you should
have an exact 1 second delay. But before starting this delay, set
TMR0 to count from external source, count from low to high transition,
then clear the TMR0 and the I/O pin tri-stated.

After the delay, put the I/O pin to low to stop the counting.
At this time TMR0 holds the upper 8 bit and the prescaler holds the
lower.  TMR0 is easily read but prescaler is unaccessible.

To read the value of the prescaler, clock the I/O pin until the value
of the TMR0 changes.  Subtract 256 from the number of clock pulses.
The result will be the lower 8 bits.

I hope this helps.

Reggie

1998\08\09@205316 by Scott Newell

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>On your program, for example you want a 1 Hz resolution, you should
>have an exact 1 second delay. But before starting this delay, set
>TMR0 to count from external source, count from low to high transition,
>then clear the TMR0 and the I/O pin tri-stated.

If you use something like a 16C74, with the CCP modules, you can do _much_
better.  I used some external logic (flip-flops) to gate the input open and
closed, and the capture function to timestamp the first and last rising edges.

I was seeing 6 digits of resolution per second, regardless of frequency.

Of course, the math for a reciprocal mode counter isn't nearly so simple...


newell

1998\08\11@230100 by Ari Wahyudi

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Yea.. I understand the problems now.. I must not read the PIC datasheet
carefull enough.

And I would like to say thank you for you all who respond to my email
about 50 MHz Freq Meter.

Thanks guy..

Regards,

-ari-

On Sun, 9 Aug 1998, Nagendra, VU2CLN wrote:

{Quote hidden}

1998\08\12@023028 by Peter Gee

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i was pretty intersted in this frequency meter.
has anyone built it ?
what type of display are people using  for it ?

do people think that an LCD calculator display would be appropriate ?

or should i just string 7 seven segment displays together ?  ie does the
multiplexer use the latency of the LED to display the frequency, or are
those displays latched ?

cheers

1998\08\12@112918 by Peter L. Peres

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On Wed, 12 Aug 1998, Peter Gee wrote:

> i was pretty intersted in this frequency meter.
> has anyone built it ?
> what type of display are people using  for it ?

Whatever you want. An ASCII LCD module or a PC connected through RS232
come to mind.

> do people think that an LCD calculator display would be appropriate ?

Yes, if you happen to be able to source an ASCI that can drive its
segments. Otherwise, no.

> or should i just string 7 seven segment displays together ?  ie does the
> multiplexer use the latency of the LED to display the frequency, or are
> those displays latched ?

What multiplexer ? This counter has NOTHING in common with discretely
built counters, or specialized chips used for that.

Peter

1998\08\13@092720 by WIL REEDER

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Terry Weeder has a really tidy little kit for this @ 46 usd. I built one a
while back and have been totally happy
with it.  http://www.weedtech.com/
good luck

----------
> From: Peter L. Peres <spamBeGoneplpspamBeGonespamACTCOM.CO.IL>
> To: TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU
> Subject: Re: 50 MHz Freq Meter
> Date: Wednesday, August 12, 1998 11:10 AM
>
> On Wed, 12 Aug 1998, Peter Gee wrote:
>
> > i was pretty intersted in this frequency meter.
> > has anyone built it ?
> > what type of display are people using  for it ?
snip

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