Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!mcnc!ecsvax!dukeac!sgt
From: sgt@dukeac.UUCP (Stephen G. Tell)
Newsgroups: sci.electronics
Subject: Re: Finding the HSYNC signal
Message-ID: <1370@dukeac.UUCP>
Date: 22 Apr 89 22:57:34 GMT
References: <8903310230.AA08623@maxwell> <16552@cup.portal.com> <772@sunkisd.CS.Concordia.CA>
Reply-To: sgt@dukeac.UUCP (Stephen G. Tell)
Organization: Academic Computing, Duke University, Durham, NC
Lines: 26


I would recommend using the National Semiconductor LM1881 chip
to decode the sync from the baseband video signal before it gets to
the modulator.  It takes a video input, and gives you TTL outputs
for HSync, VSync, blanking, field index, and burst gate, which
tell youu just about everything you could possibly want to know about
the video timing.  For your circuit you would need just the Hsync and Vsync
signals to reset your horizontal and vertical counters.

I would strongly recommend staying out of your TV set; many connect the
AC line to their power supply an chassis without any transformer, so it
would be easy to fry your circuit, computer, and yourself to a crisp.
The general principle is that if you have to ask if its dangerous to open
up and hack on a TV, stay far away from it with your screwdriver.

The modulated RF signal would have to be demodulated to baseband video
before it could be used, so why not just pick off the signal before it
gets modulated?  In order to feed both your circuit and the modulator,
you may need a video distribution amplifier (VDA) to split the signal.
(Note that this is different from an RF DA used for splitting antenna signals.)

Steve
-- 
Steve Tell:  senior, Duke University school of Engineering (please hire me).
Former Chief Engineer, Cable 13 / Duke Union Community Television.
sgt@dukeac.ac.duke.edu;     !mcnc!ecsgate!dukeac!sgt