> Hi, All!
>
> Before Christmas I asked you all for ideas and suggestions
> on a video capture device I was planning to design.
>
> Within the holiday I had a working design. At least almost working.
>
> In short this is how the design works:

... interesting details on a video sampler omitted ...

one thing which comes to mind is why you don't just get the whole field
between two VSYNC, leaving HSYNC processing to the PC (you just have to
make the HSYNC/VSYNC pulses store an "invalid" value into the RAM, e.g.
0 or 255 (or, if you also have a parity bit...). That might simplify
the hardware, and make the design less critical (you would then
just use the PIC to drive the transfer to the PC I guess...) so that
you could use a slower PIC.

As for your drift problem: isn't it just an effect of the tolerance of
the transmitter and your xtal ? you drift 400ns every 134 lines or
8576us, which is approx 45 ppm -- maybe you can put a variable
capacitor in the oscillator and tune it so as to reduce the drift.

In any event, would you like to make schematics & sources available ?
sounds like an interesting project.

        Luigi
-----------------------------+--------------------------------------
Luigi Rizzo                  |  Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it    |  Universita' di Pisa
tel: +39-50-568533           |  via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522           |  http://www.iet.unipi.it/~luigi/
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