FothTV (405-line from a PC) - KISS Circuit
 

Hi,

I've been pondering the complexity of the MkII RGB combiner, trying to come up with something simpler and consequently easier and quicker to lash up.

This is the end result, it uses the smallest number of parts I think it's possible to get away with while still "working".

This just crudely adds composite sync to the green video signal, ignoring red and blue. I've tried it with monochrome and colour DVDs and it works pretty well, considering. Field-sync is just one broad pulse which my fussy Pye monitor doesn't like, I get line-pairing as happens with the XORed syncs from the "MkII". But I do get a locked 405-line picture. Well, sort of... ;)

I'm not sure what a VHF modulator will make of it, though; I've still not built one.

But, here it is - it could be worth trying this first, then work up to better circuits later :)

(I'm not claiming originality; I found a few circuits for feeding "Sync on Green" monitors while trawling the 'net for ideas, this is a rip-off of one of them...)

So... you need this, a suitable PC and a modulator...

I should add that this requires both syncs to be negative-going, so you need "-hsync -vsync" in the modeline.

Regards, Kat

Re: FothTV (405-line from a PC) - KISS Circuit
 

Hi Kat,

I've been toying with this kind of idea for a while (also prompted by a web search). Is there any reason why the RGB signals can't be mixed with resistors? It would then at least approximate a monchrome signal (OK, so it may up the parts count by 6).

Jim.

Re: FothTV (405-line from a PC) - KISS Circuit
 

Hi Jim,

Nope, no reason at all; now I've proven this one works; guess what I'm lashing up right this minute? ;)

Regards, Kat

Re: FothTV (405-line from a PC) - KISS Circuit
 

Hi Jim, you need only three additional resistors.;)
Place a 180R at red , 680R at blue and 47R at green.
Connect them at the 47uF.

Darius