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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