Embedded OSD (Not STV5370A)

Sounds like a time/date generator for CCTV recording... Lots already exist, last one I bought was about 40 pounds in UK

have several available). Unless I needed it for part of a design I personally would not reinvent the wheel, unless it is a project to learn about.

Most OSD modules/chips work in RGB domain as they are _mainly_ used in monitors that are in RGB domain. Philips have a bunch often with I2C interface.

Work out what you actually need, i.e.

1/ does it have to be colour or monochrome? 2/ does it need black borders or grey borders around the text? 3/ does it need graphic symbols?

If you are using monochrome and simple character sets, with a border or video mixed border, you can do simple switching of video and OSD o/p, mixing can be done by reducing chroma and luminance before mixing on a simple alpha mixer[1] which exist as analog mixer/multiplier chips from many manufacturers. Ensure your alpha signal does not have sharp edges as this can cause image artifacts, especially if your clock to generate the OSD has jitter on it.

Lots of people have made OSDs and time date generators that are driven by a PIC and limited external circuitry to overlay onto a composite video stream by the above methods. There are propbably articles about doing the same thing on Circuit Cellar magazine site, I have seen various articles about this in many places.

You could use a piece of dual ported RAM that holds enough bits for a small section of the screen to overlay the data. Some timing circuit to read out the OSD data at the right time, and change the RAM contents from the micro at a time when the RAM is not being read. So if the RAM is read out over a 2ms portion of the field, you have 18ms available to update the RAM.

Most colour OSD work is done for simplicity in the RGB domain, as this requires simpler locking of line and subcarrier frequencies, hence derivation of pixel clocks for the OSD. A reconstituted composite output PAL/NTSC has both parts driven by the same subcarrier. Even studio equipment works by separating the video into at least Y/C or YUV to remove the artifacts and what phase each video stream is to each other to mix signals.

[1] alpha mixer

output = ( X * alpha ) + ( Y * ( 1 -alpha ) )

Where alpha = 0 to 1

X and Y are matched inputs on amplitude range

output is matched amplitude range to inputs

--
Paul Carpenter		| paul@pcserv.demon.co.uk
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In message , Paul Carpenter writes

Close, but I need to be able to overlay serial data, it's for recording checkout transactions with the camera output. Might be worth hacking one of the CPC units though.

Well, I'd prefer not to have to reinvent the wheel, but I really don't want to have to pay almost 1000ukp per site (four sites, five checkouts each )

Colour would be nice as I could then select for maximum contrast against a range of different backgrounds.

Would be nice to have a black outline for readability but other than that I don't need it.

Hmmm, pound sign would be nice but not essential.

Snipped lots of useful information, thanks for your reply.

--
Clint Sharp

Coulden't help but notice your application.

UK US We interface to more cash registers than anybody else.

Cheers,

Chris Moya snipped-for-privacy@aveusa.com

I was just looking at these the other day. There are a bunch of people who make parts with R/G/B and syncs out, fewer who make parts with composite video out. For the r/g/b parts you can try ST, Philips, Renesas, Fujitsu, Sanyo, Zilog and probably Samsung and Toshiba.

Fujitsu has two parts with composite out MB90050 and MB90092 listed on their site here:

but I was told one was obsolete, and I don't recall which it was right now.

I haven't used any of these in a product yet, so I can't comment on how well they perform. I also saw a few very low-res attempts using a PIC or similar along with a LM1881 (or the updated elantec version of same) to allow the micro to time out the data outputs and simply force white/black pixels at the appropriate time.