Re: TV Charater Overlay - food for thought

[Keith Doxey <ukha@xxxxxxxxxxx>]

Quoting Wayne <wayne@xxxxxxx>:

> Thanks all!
> Was wondering if this thing was an 'easy goer' but guess not... :(
>
> A couple of things spring to mind though. Taking on board whats been
> said about composite video, would a tv convert an rgb / svideo signal
> from another scart socket (assuming thats where Tivo's etc are plugged
> into) into composite video on a second socket?

No because S-Video on SCART and RGB on SCART are only ever inputs as the
same
pins are used for In and Out. Having said that, a lot of TV's WILL output
the
Composite input from one SCART to another SCART. (Often menu definable and
may
only do it whilst the TV is in Standby).

As RGB signals used Composite Video as the Sync, a SCART being fed RGB may
output a composite vesion on another SCART but an S-Video input would
output a
Black and White picture under similar conditions.

> If this is the case then
> (and a few leaps of faith are going on here) would it be possible to
> 'flip channels' by our new 'box' just while it displays the text - I
> realize that the output of that would be composite video, but for 5
> seconds (or some other manual response) or so it takes to acknowledge
> the message is it so bad? It isnt as though your focus is on your
movie
> at this point. The other thing from that is getting this 'thing' to
> release the channel and take you back to where you were before it
> started or is this something thats variable depending on how the
> manufacturers implement scart?
>

Again it is very TV/Manufacturer specific. SCART switching often depends on
a
heirachy often with AV1 being the "boss". As this is often the
RGB scart as
well it can be difficult to force another input to take priority. The other
problem is that the TV may drop back to the wrong input afterwards.

eg. My Mitsubishi TV would do the following. Assuming I have an S-Video
input
on
AV2 which grabs the SCART. I watch AV2. I then choose to watch something
via
the TV tuner by pressing "4" or whatever. I am now watching
channel 4 and it is
totally ignoring the fact that AV2 was forced.

I now use something that grabs AV1. I watch AV1. I then drop the device on
AV1.
Instead of dropping back to Tuner(Channel 4) that I was watching, it then
decides that I should be watching the still active AV2 :-(

> as a PS. did a 'Google' on the STV5730A chip Kieth talks about - to
say
> that this was a popular chip seems to be an understatement! although I
> found this http://alternatezone.com/electronics/vtg.htm
which (about
> half way down) suggests that this chip is now back in production! -
> Would this be good news? (or fiction? - cant find it on a manufactures
> web site) - although this then makes my original idea a little harder
as
> its now a case of working with chips rather than modules (no plug n
play
> :) )
>

It is a VERY popular chip for DIY type Video overlay but its days are sadly
over. Any commercial need for OSD falls into one of 3 types of application.

1. TV. These all have Teletext so the microcontroller that generates the
Text is
also used for any OSD. (In fact the whole guts of a TV can now be obtained
on a
single chip)

2. Set top box. All new STB's are for some form of Digital TV so
effectively
have a graphics card ona chip more than capable of generating OSD.

3. Security Applications. The crosspoints used for switching multiple
cameras to
different monitors now have multi channel OSD built in.

It would be superb *IF* it was back into production but the only thing I
could
find on www.st.com was the datasheet under "Obsolete Products".
Last year I
asked my Account Manager at Rapid Electronics to check on the availability
and
whist she could have obtained some I was told that it was being
discontinued
with no replacement. The only results found on st.com whan searching for
OSD
return chips that fall into categories 1 & 2 above. :-(

Keith

www.diyha.co.uk
www.kat5.tv