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'Sync restoration (how) ?'
1996\04\09@105316 by Argiris A. Kranidiotis

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[ Ok, this is *not* a pure PIC question, but I really need some help...So
don't shoot please ...]

Dear All,

       I have a composite video signal (PAL) with *no* sync pulses at all.
I  would  like  to  build  a  simple  circuit  to put the sync back (a sync
restorer).   Ideally,  vertical  & horizonal phase (and frequency -- slight
changes) would be adjustable.

-  Can  you  suggest  me any special IC's for that purpose ?  (I know about
National's  LM1882  but  it  is  too  complicated  for  my purpose).  I was
thinking to use a PIC for that purpose , but this must be an overkill...

- Any other suggestions or ideas ?


Thank you very much in advance,

Argiris A. Kranidiotis

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1996\04\09@121721 by Martin McCormick

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In message <.....m0u6eod-0000nfCKILLspamspam@spam@dc.cis.okstate.edu>, "Argiris A. Kranidiotis" write
s:
>        I have a composite video signal (PAL) with *no* sync pulses at all.

       There needs to be some sort of timing signal available which is synced
to the video signal.  The actual sync generation is simply the addition of
a pulse of the correct width of maximum black level sent at the start of each
new video frame which in the case of European PAL is every 625 lines.  One
could divide the color burst frequency down enough to provide the right
suitable frequency, but there needs to be some sort of time reference in order
to know where the exact start of the new frame is.  Some subscription video
systems send no sync, but transmit a pilot carrier over the audio so that
the decoder can rebuild a sync pulse.  The short answer is that there is no
magic way to restore sync where there is none.

Martin McCormick 405 744-7572   Stillwater, OK
OSU Center for Computing and Information services Data Communications Group

1996\04\09@134224 by Terry Yingling

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On Tue, 9 Apr 1996 17:45:45 +0300, you wrote:

>        I have a composite video signal (PAL) with *no* sync pulses at all.
>I  would  like  to  build  a  simple  circuit  to put the sync back (a sync
>restorer).   Ideally,  vertical  & horizonal phase (and frequency -- slight
>changes) would be adjustable.
>
>-  Can  you  suggest  me any special IC's for that purpose ?  (I know about
>National's  LM1882  but  it  is  too  complicated  for  my purpose).  I was
>thinking to use a PIC for that purpose , but this must be an overkill...

There is a sync generator chip available that provides all the sync signals
you'll probably need.  It is the CD22402E LSI Sync Generator.  Works with 525
or 625 line systems.  It cost $7.95 from DC Electronics.  Don't know if 800
numbers work from Athens but their number is 1-800 467-7736 or 1-800 423-0070.

Good luck.

Terry

1996\04\10@133821 by Jim Main

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>        I have a composite video signal (PAL) with *no* sync pulses at all.
>I  would  like  to  build  a  simple  circuit  to put the sync back (a sync
>restorer).   Ideally,  vertical  & horizonal phase (and frequency -- slight
>changes) would be adjustable.

Although there're a variety of timebase chips that would do this cheaply, you're
still going to need a reference to lock on to... eg you can't just re-insert
syncs from a free running timebase - (you could try locking to colour subcarrier
and dividing down - but it's not too easy in PAL..

I had been thinking that a PIC would be good for doing an intelligent sync
capture (look for absence of picture etc) and locking a pll to the output of
the Pic - haven't done the sums tho'....

Jim

1996\04\10@192328 by Ken Parkyn

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>>        I have a composite video signal (PAL) with *no* sync pulses at all.
>>I  would  like  to  build  a  simple  circuit  to put the sync back (a sync
>>restorer).   Ideally,  vertical  & horizonal phase (and frequency -- slight
>>changes) would be adjustable.
>
>Although there're a variety of timebase chips that would do this cheaply,
you're
>still going to need a reference to lock on to... eg you can't just re-insert
>syncs from a free running timebase - (you could try locking to colour
subcarrier
>and dividing down - but it's not too easy in PAL..

If the colour burst (or even a remnant of it) is present, it should be
possible to detect this & then at least generate sync pulses for the
following lines, meaning you'd miss one line sync. Once this has been locked
on to, you'd then need to look for a missing pulse at the vertical interval
and derive the vertical serration sequence. around line 8 or 9 the colour
burst starts again. This again could be detected and your insertion sequence
initiated. (Perhaps this is where the missing line could be tolerated, as
it's already in the vertical area.)
Kenneth
The lion and the calf shall lie down together,  but the calf won't get much
sleep....

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