Sir Galahad and the Holy Grail (Laptop LCD to VGA conversion)

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Ex-parrot's picture
Joined: Dec 20 2003
Posts: 6835

For everyone who's been looking for a really simple (albeit lacking in some quality) Holy Grail circuit, here's one I stumbled upon:

And an implementation of it: (mirror as the original is hosted on a DSL connection)



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Eudimorphodon's picture
Joined: Dec 21 2003
Posts: 1203

This circuit came up a few years ago. It's a cute hack, but it doesn't do much to disprove the statement that you "can't just make a cable to plug a laptop LCD into your VGA port and use it like a monitor". This hack relies heavily on the fact that these particular LCD panels use the same pixel clocks and timings as a fixed-frequency VGA monitor, and use easy to work with (TTL) voltage levels. These panels were specifically manufactured to work with trivially modified standard VGA chips. (All you need to provide on a chip to drive one of these panels is a modified RAMDAC which exposes the digital signal before the analog conversion. Modern chipsets have much more sophisticated LCD panel support.)

Most panels simply *won't work* with something this simple. You could probably apply a similar circuit to a higher resolution *TTL* panel, granted, but at the very least you'd have to program your video card to output a mode with compatible timings. (Unlike these panels, a higher resolution panel probably *won't* match up so nicely with a common video mode.) As to applying this to a "modern" (less then seven or eight years old) panel, well, good luck. At the very least you'll almost certainly need to buy some hard-to-find driver ICs to correct the signaling levels to something usable. *And* need to program a custom video mode. *And*... well, you get the idea.

This is the exception that proves the rule, basically.


DrBunsen's picture
Joined: Dec 20 2003
Posts: 946
There are allusions to a simi

There are allusions to a similar (or identical?) possible hack in this old thread.


Damn the Torx screws, full speed ahead!
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