Hi Hernan Freschi

If you don't want to use the 1881 (great ic!) you could grab a 12C508 and
program it for detect the pulses, I think that the best would be something
like the 16c621 (they have 2 comparators built in, but are more expensive)
the 12C508 are very cheap, and you could make it to detect the vertical
and horizontal sync and let you know to a bigger IC via another pin.

a good source to figure it out how to do it is looking for the tv decoding
cable circuits (a.k.a. "Decos" in my country ;-), those usually detect, using
operational amps, the supressed sync of the video encoded signal to
lock on, the code is very interesting to take a look, there are over there
a lot of that, but you could start looking for the "3chi" code Decos.
if they can lock on a supressed sync video signals, do that with a good
video signal it's far to easy :-).

BTW: if you use Pal-N, are you from Argentina?, if so, did you try to
find the LM1881 in GM Electronica or CIKA ?, I usually get this ic from
those stores.

If you can't find any 3chi code, i can look for it, contact me via private
and I'll send you the asm if you need it.

good luck

Leo


At 03:35 PM 9/16/02, you wrote:
>Hi there. I'm playing around with video and PICs, and I'd like to
>overlay signals on the video.
>Question is: How do I detect the VSYNC and if possible HSYNC signals?
>
>**** I don't want to use ICs like LM1881 or EL4581, because I can't get
>them at my local electronics store, and I have to order them from
>somewhere else (and wait!). ****
>
>Is there a way of doing that with op-amps or something? All I want is a
>pulse on the PIC port when VSYNC is present, so I can trigger the
>software.
>
>(BTW, the circuit would be for PAL-N).
>
>Hernan Freschi
>
>--
>http://www.piclist.com hint: The PICList is archived three different
>ways.  See http://www.piclist.com/#archives for details.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.