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[DPRG] Re: [D P RG] Converting laptop LCD's

Subject: [DPRG] Re: [D P RG] Converting laptop LCD's
From: Kenneth Maxon kmaxon at qwest.net
Date: Sat Jun 4 18:06:58 CDT 2005

The panels used in most laptops are VGA compatible.  

That said, there is a striking resemblance between the data structure and timing used in VGA signals driven to a monitor and the parallel data signals driven to a TFT LCD panel.  The resemblance comes at the higher level of the protocol if you consider a pixels worth of data to be equivalent between the two systems (even though one has 3 analog values to represent R,G&B, while the other has 3 digital (5,6or8 bit) numbers to represent R,G&B) then everything else is basically identical.  From this stand point, interfacing to an LCD display from digital circuitry is easier than VGA as you don't the need the DtoA converters and impedance driving of the cables & phase alignments of pixel clocks between sender and receiver are taken care of.

DVI opens up a whole other can of worms.  DVI is just a commercial standard that covers standards on how to interconnect video + audio between two pieces of digital equipment.  The bigger problem in using DVI is that it is not an open spec.  There are legal fees & licensing agreements involved, requirements to use only approved connectors & wiring with impedance matched spec's...   What they're trying to do is make it so that every DVI piece of equipment is 100% interchangeable and that the consumer has a "pleasant" experience with DVI.  Of course most of this precludes it from inclusion in amateur projects...

     -Kenneth
  ----- Original Message ----- 
  From: DeltaGraph at aol.com 
  To: kmaxon at qwest.net ; wecole at ev1.net ; dprglist at dprg.org 
  Sent: Friday, June 03, 2005 11:57 PM
  Subject: Re: [DPRG] Re: [D P RG] Converting laptop LCD's


  Kenneth or Someone:

  Do the Laptop LCD panels have an integrated controller?
  I thought I heard someone describe them as having like an analog VGA interface?
  Is this not true?  It seems to make sense that they would not have analog inputs except for the high pin counts or fast logic to clock all those bits.

  I find it interesting that the cheap LCD panels have analog VGA interfaces and the more expensive have DVI (where I would think it takes more to digitize analog VGA signals).

  Now, maybe the issue with DVI is cables are probably less available or harder to make.
  I figure somewhere there is a plant where a slag of plastic pellets and copper flows in one end and VGA cables flow out the other where they are dumped into cargo containers -- making the choice for low end video monitor manufacturers -- analog VGA.

  My question would be if any of these LCD panels  accept analog VGA, might a DVD player with component RGB output get you real close to what you need assuming that the LCD controller would accept NTSC timing & come to think of it interlaced video too -- unless using progressive scan output DVD which is maybe more likely present with one that has RGB outputs I would think.

  Also, if a DVD player with a DVI output is helpful then the solution may not be cheap,
  one I saw:  http://www.projectorcentral.com/bravo_d1.htm

  And it does not come with a DVI cable. Those things are pricey!

  -Ron


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