IC - VGA to PAL

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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


Re: IC - VGA to PAL


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check whats used in the video output on cctv dvr , should work and will
be cheap

Re: IC - VGA to PAL


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http://www.analog.com/en/digital-to-analog-converters/video-encoders/ad725/products/product.html

Dave.

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Re: IC - VGA to PAL


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.)

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http://www.analog.com/en/digital-to-analog-converters/video-encoders/ad725/products/product.html
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Re: IC - VGA to PAL


(resent coz Windows Live Mail is a crap Newsgroup client)

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.)



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http://www.analog.com/en/digital-to-analog-converters/video-encoders/ad725/products/product.html
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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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Check out my Electronics Engineering Video Blog & Podcast:
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Re: IC - VGA to PAL



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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

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Actually, that's exactly what happens now! The screen is a small LCD from a
PSone.
pic -
http://www.retroleum.co.uk/wp-content/uploads/2009/05/psonelcd_front.jpg

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
http://www.analog.com/en/digital-to-analog-converters/video-encoders/ad725/products/product.html
I
think it would work for what i need.

Anthony

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http://www.analog.com/en/digital-to-analog-converters/video-encoders/ad725/products/product.html
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The documentation for that chip specifically identifies the need for an
interlaced VGA input at the appropriate size and frequency.

Sylvia.

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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 using can't output an interlaced
signal. Suppose try and see how i can convert from progressive scan to
interlaced (and actually read the data sheet!). Even if i drop every 2nd
line to get the correct vertical resolution i'm ok with that (is it as
simple as a clock divider? i wont have a chance to try it for a while).
Otherwise i'll just give up and buy something like David Eather mentioned.

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http://www.analog.com/en/digital-to-analog-converters/video-encoders/ad725/products/product.html
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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.


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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.

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It's called TV OUT or something similar. Pretty straightforward, really.
Either your video card has it or it doesn't, simple.









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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.

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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.






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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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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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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.

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that's too much like hard work.

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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?)


Re: IC - VGA to PAL


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Sent: Thursday, February 18, 2010 6:55 PM
Newsgroups: aus.electronics
Subject: Re: IC - VGA to PAL

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I don't know what stm is, but i'm actually running in DOS (I just need a
non-multitasking OS because timing is super critical)

On this page http://www.epanorama.net/circuits/vga2tv/psergio_circuit.html
(it's ancient)
I used this program: http://www.epanorama.net/circuits/vga2tv/vgatv2a2.zip
to convert the video output to an interlaced signal. IT WORKS! but the hsync
signal is inverted!! My old CRT can display the picture, but nothing on the
little Psone LCD. I don't think it can make sense of it.

Can't believe i don't have anything here that can invert the hsync signal!

 


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"SVGA Text Mode"  with a couple of hours work the linux source can be
compiled with the free version of turbo-c for dos. like the label says,
text mode.  DOS on a TV :)

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hsync inversion can be done with software... or a transistor.

bye.


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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.

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