Hi Igor.

I've done work for PICs using correlation with fixed frequencies.
For PLL I was using hardware but it seems possible to do it in
software as well for low frequencies. ( the same ideas )

In your case highest frequency is 500 Hz which is 2 mSec
With 20 MHz PIC and (for say) 20% of PIC time used for PLL
software you'll have 2000 clocks per sine period.
Looks quite doable.

With what speed the primary frequency can change ? ( Hz/sec)
Do you need just to decode what is frequency/amplitude/phase
or you really need to do PLL on that ? The more details the better


WBR Dmitry.


Igor Pokorny wrote:
>
> Hello Dmitry,
>
> you mentioned correlation. Do you know some methods how to do this with
> PICs.?  I would like to do PLL of the incoming signal very much (300 to 500
> Hz for about 100 to 300 miliseconds) but I am not able to find any algorithm
> that would be able to filter a signal and/or to synchronize ADC by a proper
> way.
>
> Igor
>
> -----Original Message-----
> From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On
> Behalf Of Dmitriy A. Kiryashov
> Sent: Sunday, February 23, 2003 12:54 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [pic]:CCP Capture mode
>
> Greetings Scott.
>
> What if the first pulse you've captured is noise/wrong pulse?
> You lock onto it and miss another one which is right.
>
> Why not filtering approach or correlation ?
>
> WBR Dmitry.
>
> Scott Dattalo wrote:
> > OTOH, if there's a potential error source that can be identified, then
> > there may be a potential fix to remove it. I can't see any *simple* fix.
> > I'm not going to add extra hardware, and I really don't care to add extra
> > inefficient software like the looping solution I proposed. However,
> > another simple solution could be to inhibit the CCP module:
> >
> >     MOVF    CCP1CON,W             ;Save the current CCP mode
> >     CLRF    CCP1CON               ;Disable the CCP module so that
> >                                   ;no new events are captured while
> >                                   ;we're reading the last captured event
> >     MOVFF   CCPR1L,TC_CaptureLo   ;Save the time for the last edge
> >     MOVFF   CCPR1H,TC_CaptureHi   ;
> >     MOVWF   CCP1CON               ;Restore the CCP mode
> >     BCF     PIR1,CCP1IF           ;Clear any spurious interrupt.
> >
> > Has anyone tried something like this?
> >
> > Scott
>
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