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From: myers@hpfcdj.HP.COM (Bob Myers)
Newsgroups: sci.electronics
Subject: Re: Changing video to VD, HD
Message-ID: <17660091@hpfcdj.HP.COM>
Date: 21 Aug 90 18:35:17 GMT
References: <1702@oucsace.cs.OHIOU.EDU>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 43

>	Question -- Does anyone out there have a circuit
>	that will get these signals out of a NSTC video 
>	signal?

Assuming that you have an NTSC *baseband* signal to work with (meaning that
it's already been demodulated off the RF carrier):

1. Several ICs are available which do just this; some good examples are found
   in the Motorola _Linear_and_Interface_Integrated_Circuits_ data book 
   (Section 9).  Assuming that you want to go from NTSC video to RGB outputs,
   look at the TDA3330 color processor.

2. On the other hand, if you're just talking about monochrome, stripping the
   sync off is relatively easy.  There's really no need to strip off the
   sync prior to sending the signal to the video amplifier, as the CRT is
   already in blanking during this period.  (NOTE: This assumes that the
   monitor includes some form of a "DC restore" after the video input, to
   detect the blanking level on a composite video signal.)  You will need a 
   sync separator to generate signals for the deflection circuit, though.  
   The typical way is to feed the composite signal (possibly inverted, or sync 
   positive, depending on your design) to a transistor that is biased in 
   cutoff, such that the sync tips turn the transistor on.  In other words, 
   only the sync tips get through.  What you get out is composite sync - both 
   horizontal and vertical together.  These can be separated by using high and 
   low pass filters, as the H and V frequencies are quite far apart.  
   Actually, an HSYNC input is often quite happy receiving composite sync, as 
   it's just looking for edges.  Therefore, you might be able to simply 
   low-pass filter the CSYNC signal to make VSYNC.  Buffer, etc., to get to 
   your desired level (TTL or whatever).  Which brings up another point:

3. Are you certain that your CRT/associated stuff is set up for NTSC video
   rates? (60 Hz *interlaced* vertical, about 15.75 kHz horizontal?)  If these
   are "computer surplus", they may not run at these rates, which are slower
   than many of the standard timings used for computer displays.

Good luck!


Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
myers@fc.hp.com                          |  sentient life-form on this planet.