Date   : Thu, 19 Jan 2006 06:15:48 -0000
From   : "Mike" <profpep@...>
Subject: Re: Master to SCART

A few thoughts.

There is 5V peak coming out of the BBC. Video input is supposed to be 0.7V -
a calculated value would indicate 460R - 470R is well close enough for
government work. Sync is supposed to be 1V, which would call for 300R in
series, so 270 or 330 would be OK.

The fast blanking input ( pin 16) needs to be pulled up to between 1 and 3V
so 100R / 120R in series is OK. The switch input on pin 8 needs to be over
2 volts to pull the set out of TV mode, (as a point, in new sets, over 9.5
Volts puts it into widescreen), so just connect the 5V direct.

Well that's the theory. The switching and blanking bits are fine, but a
quick look at my Master128 diagram, (first one to hand), shows there is 68R
in series with the RGB and sync outputs, probably to protect the BC239's in
the video outputs from shorts, as well as to match the 75R coax. So my vote
is for 390 in series with the R,G and B, and 220 in series with the sync.
The sync inputs on sets can be a bit variable though. If you have been
cursed with a high impedence sync input, the coax in the scart lead will
very likely 'ring', producing all manner of wierd sync effects. Putting your
own 75R to ground at the SCART end will usually sort this.

Incidentally, the fast blanking was originally designed to allow video
overlay, for example for the then (late seventies), expected external
TeleText boxes. It can still be done, but you then also need to genlock your
external video to the set. I did once use it to add a message box/clock to
some TV sets for nightclub.

I've got a couple of Philips monitors with SCART. I'll make up a lead next
week and report.

Mike

----- Original Message ----- 
From: "Jonathan Graham Harston" <jgh@...>
To: <bbc-micro@...>
Sent: Thursday, January 19, 2006 1:30 AM
Subject: [BBC-Micro] Re: Master to SCART


> > Message-ID: <4deacd9d22info@...>
>
> Sprow <info@...> wrote:
> > I would favour series 1N4148 diodes myself, else a larger resistor, say
> > 470R. Infact it seems odd to suggest needing 220 and 270R parts - maybe
it's
> > a typo in the translation to the webpage?
>
> The original says "220 ohm resistor" and "270 ohm resistor". See
> http://mdfs.net/Info/Comp/BBC/Monitor/BBCtoTV.rtf
>
> -- 
> J.G.Harston - jgh@... - mdfs.net/User/JGH
> There are three food groups: brown, green and ice cream.
>
>