Path: utzoo!attcan!uunet!snorkelwacker!apple!portal!cup.portal.com!mmm
From: mmm@cup.portal.com (Mark Robert Thorson)
Newsgroups: sci.electronics
Subject: Re: COMPOSITE -> TTL
Message-ID: <30171@cup.portal.com>
Date: 24 May 90 06:33:57 GMT
References: <24431@unix.cis.pitt.edu> <1015@gold.GVG.TEK.COM>
Organization: The Portal System (TM)
Lines: 30

To correct any misinterpretations of the previous post, I'd just like to
point out that the interlace is generated in the source of the video signal,
by adding a half-line at the end of the frame.  This shifts the next frame
by a half-line in the vertical dimension.

Your monitor's selection between interlaced and non-interlaced modes probably
just changes the speed of the sync pulses the monitor is expecting.

The original poster wanted to run a signal from a VCR into a video
monitor from an ASCII terminal.  This is possible, but not trivial.
The cheap video monitor in the terminal requires a sync signal.  To
get this from a composite signal, you need a sync separator.  There
must be one in the VCR, so it may be possible to find a suitable signal
in there.

So maybe you could connect the composite signal to the video input, and
probe around inside the VCR with the sync input.  As I've described in the
past in this group, I once modified a TV set to receive pay-TV signals
encoded using inverted sync by a similar means.

I located a trace on the circuit board which appeared to connect the video
section to the sweep circuits.  I cut the trace, and turned the TV on, and the
picture would roll asynchronously to the transmitted picture.  Then, I hooked
the suspected horz sync signal to various places in earlier stages of the
video section, until I found an inverted sync signal.  Then, I wired in
a switch to flip back and forth between normal and inverted sync pulses.

Be warned that the voltage levels might not be compatible.  Also, a TTL
input on the monitor might be too much load for a CMOS output in the
VCR.