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PIC showing images on a TV :-)

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psmll

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Hi,

Two days ago I thought in a new project, nothing serious, just for fun, put PIC processing images that can be seen in a regular TV :)

To start I choose the PIC18F2620, because it have an internal oscillator that with PLL can do 32MHz (8MIPS) and lots of ROM & RAM.

For the DAC I simple used some resistors.

This can be used, just for fun, or for example to use a TV as a out interface for an application that needs to show important information, menus...

I searched in the net, and this is nothing new, some people already did it.

Since I'm doing this for fun, I will try to do it by myself.

First, where I live the PAL is the standard, so I didn't spend time with this decision ;-)

To start I only use Black&White.

Now the most important, to do something, we need to know well how it works, this is the biggest problem.

The document to go is the "Recommendation ITU-R BT.470-7 Conventional Television Systems", but I can't find a link to download it, if you know one, please help

I searched in the net and I found several info, the big problem, is that one page for example says "x=4.7us" and other page says "x=4.5us", and I don't know what is the right one...

I was able to put PIC sending some signals to tv, but as you can see in the captured images below, the first lines are not in the right position :-( Do you have any idea what can be?

At least the other lines are OK, and the first lines not even are visible in most of the TVs ;-)

Another thing that I don't know very well are the video signal voltages, in some places says that they are from 0 to 1V and in others that are from -0.3V to 0.7V.

I first tried one DAC that only have 2 resistors and produce voltages from 0 to 1V, but it didn't worked well in some of my TVs, VCRs and PCTV card, as you can see in the second image below (from PCTV card).

So I did an DAC that can do -0.3 to 0.7V, the only problem is that it needs 4 resistors, but worked very well in all the equipment, as you can see in the frist image below (from PCTV card).

So I think that the right is from -0.3 to 0.7V. Do you know if I'm right?

I already tried so display some things and seems to work ok :)

Now the problem is that the video signal need accurate times, but I also have to put some code to do process others things...

This is just a start, maybe you can try to do something like this, and give me information :)

A test image, the first field have some bars, and the second are all white. (large images, but only 5.6KB+5.56KB) ;-)
 

btminzon

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Congratulations, this is a very nice project. You can also try to use a fpga to generate the RGB signals. There is some threads about that in this forum. So, you can free some processor´s time. Again, congratulations!!

best regards

Breno
 

jhanus

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Don't ask...(in rar is all information I collected for my collage project)

At a begining it was fun, after some time I realized that there is no room for even one mistake, literally.
1us off and there goes image down the drain, ahh, for second year collage project I choose this, while others where liting LEDs, smart move, NOT.

I did finished it, but you have to realize with 4MHz you lose 98% of time generating TV signal, and other 2% for something intelligent to do. (I exaggerate a little)

But, maybe you will like it.
Good luck. :|
 

psmll

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Hi,

At the moment I'm with no free time to continue the project, it will need to wait a little bit, I not even have the MPLAB installed...

But I will finish it ;-)

At the moment:

-I have good control of the tv signal specification, all the times need to be very accurate

-I solved the problems that I had with the top pf the image

-Now to simplify the things, the image is stored in RAM, I just change the RAM to change the image :)

-I also have done some things to 16F PICs, but because of low RAM memory the image have less resolution compared to 18F PICs

Problems:
-For now it's all in ASM, to have accurate times, but I will go to C to process the Image(RAM matrix) and ASM to draw the image.

Future(when I have time):
-Choose a nice application to use it ;-)
 

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