Hi, I'm trying to to get my hands on a chip that will convert a VGA signal to PAL. I've found a few, but they're discontinued. RsComponents, Maxim, Jaycar and googling for hours hasn't worked!
Does anyone know where i could a chip that does this?
Thanks
check whats used in the video output on cctv dvr , should work and will be cheap
Dave.
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"fuzzymonkey" wrote in news:idKdnckf-_aI_vDWnZ2dnUVZ snipped-for-privacy@westnet.com.au:
If you intend to drive a normal TV set, have you considered the scanning frequencies?
The horizontal is roughly twice as fast as the conventional 15625Hz (64us)
You may well end up with two side by images with half the scan lines!
Ray
Actually, that's exactly what happens now! The screen is a small LCD from a PSone. pic -
It can display NTSC or PAL and takes a composite or S-video connection. From VGA i connected Red, Green, Blue, Ground and HSync to the screen. It shows a very very blury double image; side by side. I figure it's because the screen only accepts an interlaced signal and the card outputs a progressive scan signal... but this is all still new to me so maybe i got it wrong. If i use something like Dave mentioned
Anthony
Wow i just realised you're Dave from the eevblog! Pays to look at peoples signatures. Love the video blog!
I was look>> Hi,
$31USD
The documentation for that chip specifically identifies the need for an interlaced VGA input at the appropriate size and frequency.
Sylvia.
Rohm BH7236AF-E2 (farnell part number 1716147 )
This won't translate the resolution or sync rate, it'll just convert RGBa+sync to PAL composite. However most VGAs should be capable of the PAL sync rate
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Wow i just realised you're Dave from the eevblog! Pays to look at peoples signatures. Love the video blog!
I was looking a similar chip on rsComponents. So the one you suggested is great, only problem is the minimum purchase quantity from analog.com is 100! I only need 1 (or 2 since i'll probably destroy the first one.)
You could try getting samples. Alternatively, Farnell have it in stock in the UK. Failing that, I might have some lying around somewhere. Definitely got some on some old boards.
Dave.
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It's still going to be quite blurry even when it's working perfectly. TV resolution just isn't that good. You will of course go the S-video route, rather than composite video, since it produces somewhat better results.
Sylvia.
From the datasheet: "The AD725 can be used to convert the analog RGB output from a personal computer's VGA card to the NTSC or PAL television standards. To accomplish this it is important to understand that the AD725 requires interlaced RGB video and clock rates that are consistent with those required by the television standards. In most computers the default output is a noninterlaced RGB signal at a frame rate higher than used by either NTSC or PAL."
Yup, that sucks. I know computer i'm us>> Actually, that's exactly what happens now! The screen is a small LCD
They sort of imply that at least some VGA cards can be configured to produce interlaced output with NTSC or PAL compatible timing, but I've never come across any information about so configuring them.
Even if you contrive to drop every alternate line, the pixel rate will still be wrong, and, importantly, the vertical sync pulses will not be set for interlaced - an interlaced field either starts or ends with a half-line - so that the total number of lines is odd (525, or 625).
You need a scan converter - which is what David Eather pointed to, and the cheap one (similar price to the one posted) I have produces a correspondingly cheap output.
It's very easy to end up wasting a lot of money like this, and LCD monitors these days can be had quite cheaply. You might be advised to take that option.
Sylvia.
It's called TV OUT or something similar. Pretty straightforward, really. Either your video card has it or it doesn't, simple.
A TV out socket will produce a composite video signal. A VGA output with TV compatible timing would still produce an RGB output with separate horizontal and vertical sync signals, but the timing would be such that it could be converted by a circuit such as AD725 into a composite video signal.
So they're different, and the "either has it or it doesn't" position doesn't stand up.
Sylvia.
It's probably just a software problem. hardware-wise all you need is a VGA compatible video card. these cards have an interlace option, you just need to turn it on.
that's too much like hard work.
that's not going to work. you need to slow the horizontal scan rate down and reduce the number of scan lines.
OTOH a CGA compatible video card runs at the NTSC tv sync rate, and converted to composite that will display a raster on most PAL TVs (I had a CGA card with a monochrome composite out in the 80s)
but seriously with a VGA card, it's just a matter of setting the right parameters. how are you setting the currnt video mode? (mswin? X? libvga? stm?)
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the following are for Xwindows but alternatives exist for most other platforms.
After ModeLine and "the label" the fields are pixel clock (in MHz), displayed pixels, hsync start, hsync end, total pixel cout for row, displayed rows, vsync start, vsync end, vertical total, then option flags
(begin modelines stolen from the mythtv website.) ===============
#702x576 @ 25Hz, 15.6kHz, itu-r bt.470 PAL, analog broadcast ModeLine "702x576@25i" 13.5 702 722 785 864 576 581 586 625 interlace -hsync
-vsync
# 704x576 @ 25Hz, 15.6kHz, itu-r bt.470 PAL, mpeg, 702 dots displayed ModeLine "704x576@25i" 13.5 704 723 786 864 576 581 586 625 interlace -hsync
-vsync
# 720x576 @ 25Hz, 15.6kHz, itu-r bt.601 PAL, mpeg ModeLine "720x576@25i" 13.5 720 732 795 864 576 581 586 625 interlace -hsync
-vsync
# 768x576 @ 25Hz, 15.6kHz, square dot itu-r bt.470 PAL, TV-monitor,
767 dots displayed ModeLine "768x576@25i" 14.75 768 789 858 944 576 581 586 625 interlace -hsync-vsync
# 720x576 @ 50Hz, 31.25kHz, itu-r bt.1358 625/50/p/1:1, RGB, YPbPr, HDMI ModeLine "720x576@50" 27 720 732 795 864 576 581 586 625 -hsync -vsync
============= (modelines stolen from the mythtv website end.)
It makes one think that IBM designed the Video Graphics Array to be capable of producing a video raster. :)
bye.
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Just buy the right video card and stop trying to convert the wrong one.
Simple - either it has it or it doesn't.
It's a laptop so can't install a new graphics card. Money is limited so i can't buy a new laptop with TV out. Space is limited so i can't assemble a PC with a card that has TV out because it won't fit.
I see your point about wasted effort... but this stuff interests me and i want to learn as much as i can about it :)
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