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Composite video

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Not sure what you meantt when you said are you sure Nige.

Colour games have been done with pic16f's, might use a similar technique to romans but still colour.

Can you give ANY example? - I don't see as it's possible (or anywhere near possible), just as Roman couldn't do it with an 18F (and I presume he had more sense then to even try :D)
 
... also noticed he used ad724 aswell, oops was this one:https://www.qsl.net/zl1wtt/images/Bar_PCB.jpg...

As you said, his project uses a PIC and a second AD724 chip to make the colour.

Don't confuse composite video colour (which is very complex!) with my simple VGA colour. VGA colour is easy as you just drive three lines R,G,B, for each pixel.

But even then, as Nigel said it's hard to do anything more than the simple 3bit colour I did which just turns the each of the RGB on/off to set one of 8 possible colours. And of course I had to transmit the whole line in ONE fixed colour, because otherwise you need 3 synchronised SPI modules to send out the 3 RGB signals at the same time.

Technically, I could have changed the colour between SPI bytes, ie; between each 8-hpixel character to make each text sharacter a different colour. But there's not much time in there for decision making as you have exactly 8 PIC instructions to load the video byte into the SPI module and to load the colour byte to the PIC port, it's possible but I did not bother as it would have been tight coding.

You could use a pre-loaded colour sequence and just clock it out, one colour byte and one data byte in an array, and clock out the 2 bytes every 8 PIC instructions.

If you really want "composite video" colour this is possible but you need a separate chip. With the right chip you can send 3 bit colour to it and it will do the rest. The good point with composite video is that the lines are much slower than VGA, so if you are happy with a low horiz resolution you might have time for colour characters or even colour pixels (very chunky pixels!).
 
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Actually the example I was thinking of might be an AVR
 
Actually the example I was thinking of might be an AVR

Again, can you provide a link to it? - I don't see how it's possible to create PAL/NTSC in software on anything of reasonable speeds (if at all?).

Incidentally, I have an AVR based test card generator - which obviously uses a PAL encoder chip to create the composite video signal.
 
You can just about create a composite B/W signal with a PIC, but not a colour one, not that I have seen anyway! Text overlay was too choppy for me when using a PIC alone, I ended up using a MAX7456 chip, I just couldn't get the sync correct, kept jittering!
 
Actually the example I was thinking of might be an AVR

I've seen a couple of nice AVR colour video generator projetcs, but they were VGA output not colour composite video. Maybe it was one of those?
 
I've seen a couple of nice AVR colour video generator projetcs, but they were VGA output not colour composite video. Maybe it was one of those?

Like I've said previous, that isn't really 'colour' - it's just three separate monochrome pictures, and is relatively easy to do.

I don't believe it's possible (or anywhere near it) to create a composite colour with a PIC or an AVR, or even devices many times more powerful.
 
Well, it is "colour video" by my definition. It works on a colour screen and makes pixels of many thousands even millions of colours, depending on ADC resolution of the 3 channels. A VGA monitor is a "colour monitor" and VGA is just one type of colour video signal. And even in a "colour TV" there are plenty of stages where all it is is three individual monochrome channels for RGB.

I do agree generating a "composite video" signal with colour using just a PIC is practically impossible. Your project did it in the best way I think using a standard colour generator circuit so the PIC just needs to make RGB colour signals. :)
 
Well, it is "colour video" by my definition. It works on a colour screen and makes pixels of many thousands even millions of colours, depending on ADC resolution of the 3 channels. A VGA monitor is a "colour monitor" and VGA is just one type of colour video signal. And even in a "colour TV" there are plenty of stages where all it is is three individual monochrome channels for RGB.

Perhaps you might have noticed the title of this thread? :D

I do agree generating a "composite video" signal with colour using just a PIC is practically impossible. Your project did it in the best way I think using a standard colour generator circuit so the PIC just needs to make RGB colour signals. :)

I don't think 'practically' comes in to it - I would say completely impossible for any PIC or AVR - could any even generate an accurate and stable 4.43361875MHz colour burst signal? (sorry, can't tell you the NTSC value, I've no reason for it to be memorized :D).
 
Perhaps you might have noticed the title of this thread? :D

Yeah point taken. :) I've probably been getting off topic talking about VGA video generation although oriignally it was to discuss issues common to both like sync and SPI pixel data out.

I don't think 'practically' comes in to it - I would say completely impossible for any PIC or AVR - could any even generate an accurate and stable 4.43361875MHz colour burst signal? (sorry, can't tell you the NTSC value, I've no reason for it to be memorized :D).

It's an interesting thought experiment. Maybe somehow running the PIC from a 4.4336 PAL colour burst xtal, or the NTSC xtal equivalent?

Then maybe some external discretes controlled by the PIC pins and the already available xtal signal... Just thinking out loud. It would be a silly way to try to do it, although I'm not sure getting some composite video colour would be "completely impossible".
 
Yeah point taken. :) I've probably been getting off topic talking about VGA video generation although oriignally it was to discuss issues common to both like sync and SPI pixel data out.



It's an interesting thought experiment. Maybe somehow running the PIC from a 4.4336 PAL colour burst xtal, or the NTSC xtal equivalent?

Then maybe some external discretes controlled by the PIC pins and the already available xtal signal... Just thinking out loud. It would be a silly way to try to do it, although I'm not sure getting some composite video colour would be "completely impossible".

'External discretes' rather proves the impossibility :D

You also only seem to be considering the colour burst, and not the actual colour data, which needs to be EXTREMELY accurately phase shifted and synchronised with the colour burst - accurate analogue output with nS timing would be difficult using a PIC.
 
.050", or 1.27 mm

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I dont thibk you'll get that in perf, you'll need a 100 leadouts to do that.

You can remove solder bridges from smd's by using desoldering braid, I usually deliberatly put too much sodler on then remove it like this.

You can salvage ram connectors from old motherboards using a hotair paint stripper gun.
 
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