Hi,

I recently got an awesome new laptop. However, soon after I got it, I found out, to my great disappointment, that it lacked a TV out. All it has was a VGA output. Not to be defeated, I began to look for ways to convert the VGA out to a signal that was compatible with my TV. After looking at several commercial solutions, I found out that ICs exist to do this. What I wanted was a self contained unit that would take the VGA signal and convert it to a NTSC S-video signal. By referring to the data sheets for the various components I wanted to use, I developed a preliminary circuit design. From this, I intend to etch a board and put it together, but I have a few questions first.

Please refer to the circuit in the attached file:

My main question refers to the capacitors. The regulator I am using required an output capacitor to remain stable (C3), and the other IC, and the oscillator both call for capacitors across the supply voltage inputs (C4,C12,C14,C15,C16). I presume the capacitors are there to ensure a stable input voltage, but are all the capacitors really required? Will having this many capacitors cause any bad effects on the circuit performance?

Also, if there are any other issues anyone can see with the circuit, please let me know. I will probably be etching the board in the next few days unless I hear something that requires me to redesign the circuit.

Attached Files

RGBtoNTSC.pdf (16.5 KB, 9 views)

 

I would suggest you need to be VERY careful, an RGB to NTSC converter will most probably not help you at all - it merely takes an existing TV standard RGB signal and converts it to a composite NTSC signal (it's just a colour encoder).

VGA doesn't provide television standard signals, it runs at a much higher line and frame rate, so you need a standards converter - a much more expensive and complicated device.

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Thanks for the reply. I know that normally VGA singnals run at higher framerates and resolutions that what I can use, but I believe the output from the laptop can be configured to the proper resolution and refresh rate. Is there any potential for damage to the laptop from a device like this?

I already have all the parts I need to make this, so unless it could damage the laptop, I will probably try it anyways, and see if it will work.

 

You shouldn't be able to configure the laptop so you can damage it, but check what resolution it will go down to first - bear in mind it's LOW for TV, less than the 640x480 of VGA - so see if it has the correct settings for NTSC.

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Since you didn't understand the function of the circuit you posted a link to I'd say immedatly stop thinking you can simply build a circuit to do this and purchase a consumer device to do it for you. It's not just a matter of frame rate and syncing the video, the formats are completly different, and not subject to simple conversion circuits. The RGB data would have to be taken and using oscilators running at very specific rates be encoded into an NTSC compatible signal.

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Yes, please buy one. Especially if it is a new laptop!

Some laptops do allow for output to tv via the vga port. In that case, a cable like this would work: http://cgi.ebay.com/VGA-TO-TV-CONVER...QQcmdZViewItem


BUT MAKE SURE YOUR LAPTOP SUPPORTS IT!!!!!!

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My laptop does not support this, this is the first think I looked at.

Please don't think I am ignoring all the people that are telling me to not make this, I realize this probably won't work, but since I have everything I need to make it, I would like to try. (if for no other reason, to see how well I can solder surface mount components) I need to be able to set the VGA to output 640x480 at 60hz interlaced. while this may not be a normal configuration for video output from computers, from what I have seen it is not impossible. From what I can tell, the damage risk to the laptop is small, if someone else can contradict this, please let me know and I will stop.

Any thoughts on my original question about capacitors? or does it change with each design?

 

Why not try and get hold of an old Commodore Amiga A500 computer RF modulator?, this included a colour encoder, plus an RF modulator, and would do what your circuit is supposed to.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk