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Date   : Sun, 05 Feb 2012 13:40:17 +0000
From   : mfirth@... (Michael Firth)
Subject: RGB to mono composite with only resistors

You could just copy the cicruitry from the BBC circuit diagram - its basically 
just resistors with a transistor on the output to give some drive (and probably
impedance matching - composite video usually presents a 75R load, which would
be quite low for a passive resistor combination of R, G, B and Sync)

Regards

Michael

On 4 Feb 2012,@22:17, Kris Adcock <beeb@...> wrote:

> LONG ago in the distant past, I had a need to convert the RGB signals 
> from (I think) a Teletext podule into a composite video feed. I only 
> needed mono, so someone supplied me with a simple circuit diagram (I'm 
> pretty sure that it used ONLY resistors) and combined everything 
> together into composite video.
> 
> I'm guessing that the different resistors gave each of the colour 
> channels a different bias that made sense in mono (red is more prevalent 
> than blue, etc).
> 
> Unfortunately I can't find the e-mail, my notes, or remember who 
> supplied me with this information. Has anyone here done this, or did I 
> dream it all?
> 
> Many thanks in advance,
> 
> Kris.
> 
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