LCD panels

[remp]

Google LVDS

The major supplier of the connection system between a laptop computer and its LCD screen seems to be the the National Semiconductor LVDS system.

LVDS = Low Voltage Differential Signalling

This system is in two main catagories

FPD-link = Laptop to Laptop LCD = short distance < 30cm (12 inches)

LDI = Lvds Display Interface = connection to a desktop LCD display <3 m (10 feet)

Both systems have a transmitter, a connecting cable and a receiver on the LCD.

The advantage of the LVDS system according to the National description
is only 4 twisted pairs are needed to transmit 24 bit colour and clock to a LCD panel which could otherwise need 50 or more wires.

To see if surplus laptop LCD's have a receiver built into the LCD I found out a number of companies offer LVDS test sets.

This is extracted from a test supplier document
This document is a test guide and it is recommended to be used when performing a functional test of a LVDS Transmitter-2xxxx (LVDS transmitter 2 pixel/clock) module and or LVDS cables for these modules. These LVDS modules are able to drive TFT displays 5v or 3.3v 1 pixel/clock or 2 pixels per clock up to 1280 x 1024 up to 24 bit colours.
.................The receivers are normally intergrated in the display................etc.

Several others said the same.
It seems a resonable assumption that receivers are fitted into Laptop LCD's

If you can get hold of a good laptop LCD and it has a 20 pin connector chances are very high it has a LVDS receiver built in.
If the lcd panel is cheap its worth thinking about how to drive it.

You need an LVDS transmitter (if it is an LVDS system) and you need to enter setting details in the computer bios.

Those two requirements are not very easy.
On a laptop the bios details are easy for the manufacturer because they know all about the LCD they are fitting.
We dont.
You could borrow a laptop, try and find the bios details, go out and buy an identical LCD screen find a suitable transmitter and hope it all works.

There is another way. Several manufacturers supply PCI graphics boards which include an LVDS transmitter and the lcd settings can be set on the board by dip switches independant of the main computer bios.

A quick search showed a few such graphics boards at about $250 - $300 dollars.

At that sort of price there is no advantage over a regular controller for about the same money.

Ebay projection panels are getting expensive. Good ones such as Sharp QA 2500 have been listed at $500.

The thing is actually very simple because an LVDS transmitter is only one chip. Its very cheap. It needs Cmos TTL from you regular video card. And it needs to know what LCD is connected. BIOS settings.

How can it get it. Is there a feature plug on a graphics board that outputs graphics digital Cmos TTL. ?
That would be handy because then we only need to find a simple LVDS board.

That still leaves the BIOS problem.

I have seen a computer board that plugs into your computer, takes in DVI, converts it to LVDS and outputs data to an LCD. No BIOS needed. No prices.

What I am looking for is a simple solution to a complex problem at around
$100 for a decent laptop LCD Maybe a good laptop panel is not that cheap. I have seen some at $10 dollars TFT colour and some at $300. If good ones are too expensive it's not worth finding out how to drive them.
$100 for the means to drive it. Guess.

I think half the problem is looking promising because all laptop LCD's appear to have a receiver of one standard or other built in. There are 4 competing systems. The most popular by far seems to be the National LVDS system.

The other half of the problem how to drive the laptop LCD is still a long way from being solved. But its getting slowly closer.

[stoko]

check out pdf files on:

www.lcdspecifications.com

my questions are:

1. can we wire some of those lcds directly on video card, somewhere between GPU and vga out, before D/A conversion?

2. can we build some CHEAP adapter, which would convert dvi signals to lcd signals such as those on pinouts?

as i understand dvi is some sort of serial connector. can those serial data be converted to parallel?

[remp]

stoko

Good link.

The whole problem with trying to even think about using surplus laptop LCd's because ebay is getting expensive is we have to try and figure out how they are connected to the laptop. What technology is involved and how it works and most importantly how can we identify panels that might be useful.

So far the only clue I have found is if the LCD has a 20 pin connector it's most likely using a LVDS connection system.

The LVDS system comes in two flavours

FPD-link for short links like inside a laptop
LDI for connection to a desktop mounted LCD.

The transmitter and receiver combinations are different for FPD-link and LDI link.

The max distance they say the FPD-link will go is from a laptop video card or motherboard to the hinge and then to the laptop LCD. They say 30 cm (12 inches).
Thats not a lot of use because for projection work you might have your computer several meters away from the LCD.

But I bet you could probably get away with 60cm (2 feet) specially on the lower resolution panels.

Still not really any good is it. You need at least 1 meter (3 feet) and 2 meter ( 6 feet ) would be better.

The options with laptop LCD's seem to be
(1) Find a LVDS LCD (20 pin connector)
(2) Find a video board that can fit close to the LCD that puts out LVDS
(3) Feed analogue into the board from either VGA, composite video or s-video.

Exactly similar to the controllers from Earthlink.

I have found several analogue boards around the $100 dollar mark. I have not yet investigated this in detail.

But now at least I know that no bare LCD panel takes in analogue, they are all digital.
Feeding them with digital is not easy
Digital would be best quality
Analogue is still ok for average use
Might be a lot easier to find an analogue board
Easier for cable length

Analogue or digital its still going to cost
The LCD panel
The controller

And if you buy an analogue controller from Earthlink or similar you have to specify the panel.

Another thing I have found out is specifying the panel does not seem all that difficult.

Assume the LVDS serial link is streaming red blue and green to the LCD. Starting at row one column one, for NTSC after 52 microseconds, the setup says hold the data steam because we now have a sync pulse. The data stream is halted for 12 micoseconds then resumes.
Meanwhile the row and column drivers have repositioned at row 2 column one all ready to start displaying the next line of data.

So what the BIOS function is doing is providing the sync pulse timing for NTSC or PAL or SECAM and the wait time between active display. These are very critical but its not hard to do.
I am not sure if its done at the transmitter end to halt data flow or at the LCD end under the Timing control IC but basically all it does is count clock pulses and knows when data should be displayed.

Also many video cards output one pixel per clock pulse or two pixels per clock pulse. The panel needs to know that information.

Also some video cards fill the frame buffer and wait until that is displayed before adding more info. Some video cards fill the frame buffer continously as fast as they can.
Thats another thing the panel needs to know.

So the bios tells the computer and LCD what to do and when to do it. Very similar to when you install a new printer or modem.

I will now start looking for an analogue board that can be fitted close to a LVDS laptop LCD and see how I get on.

[stoko]

look at this LCD pinout at:

http://www.lcdspecifications.com/tos...12C289-v30.PDF

and this DVI pinout at:

http://www.altinex.com/PDFs/ConnectorPinouts_121401.pdf

it is completely different, and it would probably need lots of electronics to interface it!

[stoko]

can anybody find schematics/diagram/pinout for any laptop so we could see how the laptop is connected to LCD?

also, can anybody find schematics/diagram/pinout for any graphics processor, so we could see is it producing same or similar signals as those LCDs requires!

maybe that way we could connect LCDs directly to GPU, withot any interface!

can anybody post abut this in the main thread! those guys probably dont know about what is going on here, and we would need all the help as possible!

i would do it myself, but my english is too bad, and i couldnt explain it to them properly!

[stoko]

about LVDS, it would be probably hard to find LCD with it!

but there are thousands broken laptops with good screens, and you can get them for few $

and on the back of all laptop LCDs there are written the manufacturer and the model of LCD!

[remp]

stoko

about LVDS, it would be probably hard to find LCD with it!

I think most laptop LCD's would be LVDS. Or a similar serial system.

They have to have a simple cheap method to get the data from the laptop through the hinge to the laptop with a very small number of wires. LVDS does that

TTL would need a lot of wires and radiate a lot of noise.

From what I can gather most laptops use either LVDS or another system very similar. A LVDS panel should have a 20 pin connector. TTL panel would have a connector with a lot more pins up to 50 or so.

http://www.idparts.com/
This link that you posted has a video of a guy removing an LCD from a laptop. If you look carefully it shows what looks like a 20 pin connector to the LCD.

[stoko]

check this out:

http://www.ixbt.com/video/images/rad...eon-scheme.gif

[stoko]

quote from:

http://www.techwarelabs.com/communit...t=1313&start=0

"Hi. electrical engineer & college proffesor here.
Working on the same project. here is the deal. tou CAN use a laptop screen on a standard PC. Configuring it to work with you analog VGA card is possible, but VERY VERY impracticle. here is what I reccomend for cost efficiency and ease. I know you want to keep it cheap.
if you dont have a main board yet (or if you do and have all the parts and pieces, IE chip, memory, etc) purchase a EBC 552 pc card. everything is built in including a TFT controller. then its just an issue of making a connector and matching the pins. these cards are made for AMD, Pentium, and VIA Cyrix, so you can buy the to match the CPU and memory you already have. they go for about 100$. kind of expensive, but its the closest
to plug and play as it gets. you'll easily spend 100 in parts and pieces to make a standart VGA card work....and you might end up burning something up.
I'm curious...what kind of interface are you going to use?? mouse, keyboard?

good luck.
voodoosi@hotmail.com
let me know how it works out "

[stoko]

http://www.google.com/search?hl=sr&i...552%22+tft&lr=