Newsgroups: sci.electronics.misc
Subject: Re: converting laptop monitors
References: 
[email protected] (directorpat) writes:

> I have a project I'm working on. I would like to adapt old laptop screens, 
> color or B&W, to be able to accept a compisite video signal. This would 
> have to be accomplished by detaching the laptop screen from the 
> keyboard/cpu then making some kind of black box to run the screen and 
> feed/convert to be able to accept composite video.
> 
> Any ideas?

Interfacing to LCD screens seem to be a frequently asked topic
without good answers or good published plans. I do not have any
plans for this and not complete information. I can only give some
hints and which will reveal that what you are trying to you could be
more complicated than you might first think.


The following part is taken from my VGA to workstation monitor FAQ
at http://www.hut.fi/Misc/Electronics/faq/vga2rgb/
It tells something about VGA interfacing to laptop LCD, the
conversion you try to do is somewhat more complicated because
you need to decide the composite video signal also.


How do I connect my VGA card to a LCD display taken from an old laptop
?

Many people have recently started to ask how to connect an LCD screen
taken from an old laptop computer. Unfortunately there is no simple
solution for this conversion because the differences of the interfaces
used in normal VGA monitor connections and the interfaces used in
laptop LCD screen. The LCD screen on laptops typically use a special
digital inteface between the graphics controller and LCD screen
itself. Those interfaces can be special high speed parallel or serial
interaces and there are many flavour of them in use. The graphics
cards inside the laptops have that special interface compatible with
the display in this laptop, but normal PC graphics cards do not have
this kind of interfaces. One problem is also that there is wide
variety of LCD display interfaces in use, so first you need to figure
out what interface is used (can get hard) and then get somewhere
information how to interface to it (information might not be
publically available). Here is a list of some LCD screen interfaces
used or in-use nowadays: 

Analog VGA (used in external LCD displays but not in laptops normally)

44-pin TTL parallel 
20-pin LVDS serial 
Digital Video(6-bit for each color R/G/B) Sync Signal,DOTCLK, 4 pairs
LVDS (used in some IBM laptop displays) 
DVI (Digital Visual Interface LCD panel digital interface from DDWG,
used for external LCD screen mainly) 

So the conversion between normal PC graphics cards and LCD display
taken from old laptop is not generally very complicated and usually
not worth of a try. To do the conversion you would first need to get
to know what type of interface that LCD screen uses, then get the
specifications of that interface, then specifications of that specific
LCD and then design your own interface for that. Very complicated and
not worth of the problem to try to do that at least if you plan to do
this for saving some money (maybe a good educational experiment for a
very good hardware/electronics expert, but not recommended for any
average electronics homebuilder). 
It is possible, but in order to get the LCD to run off a standard VGA
or standard digital video card, a converter must be bought. The
converters cost about $250+. Its often cheaper just to buy a flat
panel display. Regular flat panel displays on the market now are at
least 15" which is much larger then the most laptop LCDs out
there. The ready-for-vga flat panels for sale include the sort of
input converter that you would have to buy to make the bare LCD
work. While it seems like the converter should not cost half the price
of a new LCD display, it does. The LCD interfaces that work for old
laptop screens were made in low quantity for a few specific projects
and are designed to support numerous types of LCD. 

You can find specifications of some LCD displays an their interfaces
from http://www.flat-panel.com/tech.htm. 



-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/