PIC OSD - Any Experts out there?

Hi, I have a few questions regarding the OSD project found here:
**broken link removed**
I have had no luck getting this circuit to work, it displays a very very blurry representation, but the sync is all over the place, I thought about using a LM1881 chip, but it's more fun to try and get it working without.

I dont know if anyone is familiar with this, I have had no response from Bruno, it seems as though he has disappeared!

I have checked the oscillator and it appears to work, I can send video out, and you can just about make it out, but its very "jumpy", i've tried changing the clip level but to no avail, I have seen a project similar in AVR without a sync chip, so i'm guessing it is actually possible.

My video signal is a PAL - I, UK standard Composite input.
I have looked on Rickard's page:
**broken link removed**

And it states that the horizontal sync is 0v, yet according to the OSD page, it is triggered at 0.625v, is this correct?

There is no information about the Vertical Sync pulse as such on Rickard's page, but on the OSD page it states:

Yet it looks as thought it is only looking for one pulse duration in the C code provided on the OSD page.

Has anybody got this or something similar to work at all?

The code for the OSD is for Mikro C btw.

Any help would be appreciated.

Cheers

Wilksey

Wilksey said:

I have had no luck getting this circuit to work, it displays a very very blurry representation, but the sync is all over the place,

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If the code is OK, then it sounds like the level setting to detect the sync pulses is off.

There is no information about the Vertical Sync pulse as such on Rickard's page,

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They show this diagram on Rickard's page:

If you want to do OSD, use an OSD chip and use the PIC to control it, this gives perfect OSD, just like your VCR or satellite receiver.

Only problem is sourcing an OSD chip that you can obtain a datasheet for.

@kchriste

Yes, I thought that, but I cant seem to get the right level, Which is why I was wondering if there was anything obvious with the code, or if anybody has got this project working.

@Nigel

I have seen the MAX7456 in action, and it is a nice chip, I know others have mentioned a ST5730 and a NEC chip, the problem is the chips tend to be quite expensive, especially the MAX chips.

The reason I am looking at a "chipless" OSD is I want to keep the cost down, my plan is to make a OSD inline system, where a laptop can interface with it via USB or 232, and send text to the PIC to output the text data on a video that is playing, this is a "give away" idea for a local community center where they have deaf people and they can play standard training videos but with a pre-timed text overlay.

I have a 18F4550 chip, ideally would want to write the code in C18, as it is a free proposal.

So any ideas anyone has about cheap OSD chips, or an easy way to use the LM1881 with a PIC, or any ideas for the PIC OSD code are welcome.

I dont require colour, just black/white text overlay.

Wilksey

Wilksey said:

The reason I am looking at a "chipless" OSD is I want to keep the cost down, my plan is to make a OSD inline system, where a laptop can interface with it via USB or 232, and send text to the PIC to output the text data on a video that is playing, this is a "give away" idea for a local community center where they have deaf people and they can play standard training videos but with a pre-timed text overlay

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No need or want to use a PIC there. The "closed captioning" function has been an embedded part of the NTSC broadcast and VHS and DVD for many years. I'm sure it exists for PAL too. And just about every TV has a Closed Captioning display function if you just work through the menus to turn it on!



This doesn't look right at all. The output drive will conflict with the existing signal.

I've seen other superimposers like at **broken link removed**
The schematic is way more complicated, can't say if it's "necessary" or not:


I do have an interest in a video superimposer myself, I've got a number of apps where that might be useful.


**broken link removed**

Oznog said:

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This doesn't look right at all. The output drive will conflict with the existing signal.
...

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It's ok, it's the same as a number of one-PIC OSD circuits over the years. The PIC output pin is toggled to high-impedance, so it on;y overwrite the video signal when it is writing to the screen.

The problem with the sync jitter is because of the method used for sync detection, the PIC is detecting the sync pulse as a DC voltage threshold, but the video signal is AC coupled through a capacitor and will float a bit depending on video content. You will probably find if you use a blank video signal like bluescreen from your DVD it will probably sync ok.

You can improve the sync detection by using a single transistor as a sync separator, and feed that into the PIC input.

@Oznog, the video's do not have closed captioning, they are pre-recorded for training at like colleges etc, it's not for a standard TV broadcast.

@Mr RB,

Yes, that is the way I understand it to work, adds 1v or 0v to the signal to represent a black or white pixel and grey values in between.

Interesting about the Sync Jitter, I have only tried it with what I have at home, which is an analog CCTV camera with BNC output and TV with composite input.

I will get a scart - composite conveter and try it on a DVD / VCR output with just the still image displayed.

Would you be so kind as to post a simple diagram of how to use a transistor as a sync seperator in relation to the existing circuit? Will it affect the video because the input and output are joined when using the transistor?

Thanks for all the help.

Wilksey