measure the xtal

[savnik]

I want to use timer0 in order to see in the LCD the frequency of crystal (internal clock). Or external on RA4
But I do not know how I begin.
I want use it , for measure xtal.



' 16F877A

DEFINE LCD_DREG PORTD ' Selection of the port D
DEFINE LCD_DBIT 4 ' Selection one RD4 with RD7
DEFINE LCD_RSREG PORTD ' RS on port D
DEFINE LCD_RSBIT 2
DEFINE LCD_EREG PORTD ' E on port D
DEFINE LCD_EBIT 3
DEFINE LCD_BITS 4 ' Mode 4 bits
DEFINE LCD_LINES 2 ' 2 lines

DEFINE OSC 4

OPTION_REG = %00001000

start:

LCDOUT $FE,1,#TMR0

goto start

[skimask]

To measure something, anything, you have to have an accurate timebase. To measure the internal clock of the PIC, using that same internal clock as your timebase as you've shown in your brief example, doesn't work.
Do you have an o'scope?

[savnik]

To measure something, anything, you have to have an accurate timebase. To measure the internal clock of the PIC, using that same internal clock as your timebase as you've shown in your brief example, doesn't work.
Do you have an o'scope?
Yes i have.
Or how to measure a xtal on RA4;
I want to measure the frequency of a oscillator with xtal or from a signal connecting to RA4

[skimask]

Yes i have.
Or how to measure a xtal on RA4;
I want to measure the frequency of a xtal or from a signal connecting to RA4

So you want to make a frequency counter then...not measure the internal frequency of your PIC...

[savnik]

So you want to make a frequency counter then...not measure the internal frequency of your PIC...
Yes.I want to measure the frequency of a oscillator with xtal or from a signal.

[skimask]

Yes.I want to measure the frequency of a oscillator with xtal or from a signal.

One of the easiest ways I can think of off the top of my head...

Use PBP's COUNT command...

But that's only good up to about 125Khz when the PIC is running at 20Mhz.

So, you could 'pre-divide' (like the various prescaler/postscalers inside the PIC) the incoming signal using a divide-by-x chip, like maybe a 74193 or something similar.

Feed the input signal into the 74193, take the output from the 74193's Qd output, which will be a divide-by-16 output, and will effectively increase PBP's COUNT commands range up to about 2Mhz (with a decrease in resolution of course).

Cascade 2 of the 74193's back-to-back, and you should be able to measure signals up to about 32Mhz (which is the effective limit of the 74LS193), using PBP's COUNT command.

[Acetronics2]

Hi, Savnik

An easy solution is to use an external RC circuit and use ... RCTime ( 16 Bits result ...) !!!

calibrate RCTime ( low drift components !!! ) with a Known Freq XTal ...

With another XTal The Result will be proportionnal to the XTal Freq change ...

That's all, Folks !!!

Alain

[skimask]

Hi, Savnik
An easy solution is to use an external RC circuit and use ... RCTime ( 16 Bits result ...) !!!
calibrate RCTime ( low drift components !!! ) with a Known Freq XTal ...
With another XTal The Result will be proportionnal to the XTal Freq change ...
That's all, Folks !!!
Alain

Won't the output from RCTime be a logarithmic response, in other highly non-linear? You'd probably have to do some serious math to get accurate results.

[Acetronics2]

Won't the output from RCTime be a logarithmic response, in other highly non-linear? You'd probably have to do some serious math to get accurate results.

Hi, Skimask

you Just forgot The XTal range won't be from zero to infinite ... 1 to 20 ... may be.

But, as always, I'm not so sure of what our friend intends to do ...

Alain

[savnik]

But, as always, I'm not so sure of what our friend intends to do ...
I have done a frequency meter with prescaler (256) from 10-1400Mhz.
I did it with pbp(tmr0) and asm.
But now i want to make a frequency meter from 0 -10 Mhz with only pbp.

[skimask]

I have done a frequency meter with prescaler (256) from 10-1400Mhz.
I did it with pbp(tmr0) and asm.
But now i want to make a frequency meter from 0 -10 Mhz with only pbp.

Well, I gave you an idea that I thought was fairly good...whether you use it or not is up to you...either run with it or don't...

[Acetronics2]

Hi, Skimask

I'm out on this one ...

I thought at first Savnik wanted to build some kind of XTal "identifying Gizmo" ...

For a Freq meter, I never found simpler than The µChip AN 50 Mhz freq meter :

1 16F84
1 74HC 132
1 Input Fet
1 LCD ...

rather simple. But works fine. ASM program ...of course.


links to clones :

http://www.sixca.com/eng/articles/fc50/index.html

Note their PCB is to re-design ... too close layers in the P.A. section ... I couldn't measure over 7-8 MhZ with their design.

Got 50+ Mhz with a re-design of PCB ...

and :

http://www.sprut.de/electronic/pic/projekte/frequenz/freq.htm


Also simplified ...

http://l.lefebvre.free.fr/freq/freq_01.html

And the last one :

http://www.artra-qrp.com/fp50/fp50.html



Alain