External LCD screen connections

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nicksen782
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External LCD screen connections

Post by nicksen782 »

Hi all!

I have been given a nice LCD screen. It is 5.7 inch TFT with backlight. Also has resistive touchscreen. It would be cool to throw a small micro at it and use it for controls but that isn't that important to me. I want to see the game screen.

Anyway, the Uzebox uses RGB332 and a resistive DAC which sends the color values to the AD725. One pin each for red, green, blue on the AD725. This screen that I have (CLAA057VA01CW) is a parallel RGB (6-bit) interface. That means that I need digital values. My thought is that I should green-wire from the Uzebox MCU (the PORTC pins for each video value) right to the bit 0-5 of each color (RGB) of the external display. I would need to ground (or tie high?) the unused bits of course.

Anyhow, perhaps this thread may be helpful to someone else who has an RGB screen.

Question: Will the image stretch across the screen? The screen is 640 pixels wide. If not, how can that be fixed? I'm looking for minimal/none code modifications. I'm not opposed to using a middle-man micro to smooth things out if required.

Datasheets:
http://www.analog.com/static/imported-f ... /AD725.pdf
http://beyondinfinite.com/lcd/Library/C ... VA01CW.pdf
CunningFellow
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Re: External LCD screen connections

Post by CunningFellow »

possible.

It will be hard work though.

The intermediary microcontroller/FPGA is going to need to scan-double the lines OR if it has enough memory de-interlace.
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nicksen782
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Re: External LCD screen connections

Post by nicksen782 »

So, connecting RGB from Uzebox to the RGB lines of the screen isn't going to work? Or, would I just get a small screen in the corner?
CunningFellow
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Re: External LCD screen connections

Post by CunningFellow »

Just connecting the RGB wires and doing nothing else will get you no picture.

You need to provide a dot clock as well.

The syncs would need to be changed/extended.

If you did these two things but still did not scan double the lines then you would end up with a fat screen than only took up half the vert resolution.

To get a picture of correct aspect ratio you would need to read a line to RAM on the secondary CPU/FPGA and then play it back 2 times.

Sounds a lot easier to get an LCD that does TV line frequency. Save/Give that VGA LCD you have for a rasberry Pi
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nicksen782
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Re: External LCD screen connections

Post by nicksen782 »

Question 1: So, connecting the clock, enable, hsync, and RGB lines from the Uzebox isn't enough? Would I just get the small image that doesn't take up the full width and height? Would I get anything at all? I would like to understand that a bit better.

Question 2: A micro would need to send each row twice then? So, the width would be fine it would just not be tall enough? This would create a stretch effect if I sent each line twice, correct?

Actually, maybe I don't know what I'm talking about but that doesn't seem all that bad other than needing a middle-man micro to handle the conversion. Then, how does a normal screen know how wide and tall to make an image? Does NTSC have all the same dimensions then?

Thanks for your answers so far!
CunningFellow
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Re: External LCD screen connections

Post by CunningFellow »

Without having a 2nd micro/fpga to fix things up you will get no picture and damage the lcd (if left run for AGES)

Remember the uzebox has composite sync and the lcd needs h/vsync. Also the dot clock for lcd is not the same as clk on the uze.

If the 2nd micro doesnt scan double you will have a short wide picture.

If it was my project id be setting aside 20 to 30 hours to do it. Thats a lot of work when you can buy an lcd that does work off ebay for 20 or 30 bucks.
CunningFellow
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Re: External LCD screen connections

Post by CunningFellow »

Oh - and yes NTSC defines everything in time.

X many milliseconds for this. Y many milliseconds for that.

Uzebox carefully creates a tv picture with the correct times, the tv accepts it.

That LCD is expecting a drum to march too as well as close to VGA timming rather than NTSC timing.

SO you want to find a TV lcd rather than a vga one. The vga one is more suited to a rasberry pi
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nicksen782
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Re: External LCD screen connections

Post by nicksen782 »

I get it now. Thank you.

30 bucks on eBay? What would I specifically look for? I've been eye-balling a 5 inch NTSC LCD from Adafruit now. Under 150$.
CunningFellow
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Re: External LCD screen connections

Post by CunningFellow »

Baby monitors and car reversing screens on ebay are all candididates.

The other option is to dumpster dive for a broken portable dvd player. They all had tv speed lcds
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nicksen782
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Re: External LCD screen connections

Post by nicksen782 »

Found this: Samsung DVD-L200 . Takes 8.4v DC. Battery is dead though and no power cord. Screen looks ok. I'm going to hook it up to a bench power supply and see what happens. It'll look pretty cool. Plenty of room for an Uzebox PCB.
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