2. LVDS cables

Some words about LVDS interface to LCD TFT screens .

For those who want to know better - please read this Wikipedia

Almost all modern laptop's (and monitor's) screens are LVDS types, it is type of serial connection to data source .

In short, LVDS is low cable count connection type, made as twisted pairs of data R G B (red, green, blue) plus clock data .

In each LVDS pair exist Positive(+) and Negative(-) wire , and those Positive and Negative must match in LCD socket and controller socket for proper work.

Unfortunate, various screens have various LVDS hardware connectors, like 14, 20, 30, 40 pins and various shapes.

For example 20 pins connectors can look different and use different sockets, but signal pin assignment is the same in both of them.

Also for example, the same looking 20 pin socket in two displays, could have completely different signals at the same pin's numbers, they are scrambled in different way.

The same differences are for all types of connectors, like 14, 20, 30, 40 or other pin sockets.

Signals always should be check with datasheet of particular display.

Many times you can use datasheet of similar display and then check for example positions of GND(using multimeter) to be sure, that order of signals are identical.

Usually, GND pins are "fingerprint" of type of cable we must use. Always check twice or more to be sure.

It is not all, another important for LCD is supply power Voltage, most of screens works at 3.3V but there are some 5V and even 12V.

But it is not all, there is also backlight, it is ambient light behind the TFT screen, that made picture visible for us.

Here we have CCFL lamps, those are driven by piece of electronic named CCFL High Voltage driver, usually controlled by BL(on/off) and ADJ(dimming) control, and powered usually by 12V-20V.

Latest LCD displays are backlit by LED diodes, in that case LCD connector have special input for LED power, usually along with BL(on/off) and ADJ(dimming) control if screen include LED driver, elsewhere there are only raw LED wires and we need to use external LED driver.

More details are there 8. Backlight

LVDS cables are able to deliver signals to various resolution screens, so they are able to deliver serial data 6 bit or 8 bit at 1 channel (odd bits) , some are works as 6bit or 8 bit at 2 channels (odd and even bits).

As last, I must mention that one pair can transmit not only data for one color, but bits of colors can be scrambled depend of LVDS receiver chip, used in particular LCD display.

Well, all above looks not easy and indeed is not.

So before start to work with any LCD display, first of all, look for datasheet of your display and read it.

In datasheet, are included most important information you will need :

- resolution of screen

- power supply Voltage

- signals to pin assignment

- what LVDS signal is used (ex. 6 bit 2 channels)

Another practical advice, is that LVDS cables are quite expensive for various screens,

so NEVER THROW AWAY LVDS CABLES from your laptop's screen. If you removed screen from bracket. always KEEP his LVDS cable, the reason is simple, that cable we can reuse for our purposes with our screen. That way we can save time and money for searching and buying cable for particular LCD screen.

Of course, I can imagine many situations that we will buy LVDS cables if we really need, and it is OK.

Is good idea, to keep also all screen's covers and brackets, as it help finally to reuse complete screen's cover with LCD display.

Also original CCFL lamps inverters can be reused, so keep them, they always fits in brackets as "original" :) hehe .

OK, let say we have screen and his LVDS cable used in laptop, as next we must know what type of control board we use with screen.

Especially what socket and LVDS signal pin assignment is used in that particular control board.

Here is good news, it looks like in the cheapest (those are most interesting) universal LCD controller boards, are the same LVDS ports, it is 2mm space standard 2 row goldpin socket, LVDS signal assignment are the same in all controllers, described as 8 bit 2 channels.

Controller Signal map looks like that :

2x15pin (the black Connector):

Pin Definition Description

1 LCD-VDD Power for Panel

2 LCD-VDD Power for Panel

3 LCD-VDD Power for Panel

4 GND Ground

5 GND Ground

6 GND Ground

7 RXO0- LVDS ODD 0 - Signal

8 RXO0+ LVDS ODD 0 + Signal

9 RXO1- LVDS ODD 1 - Signal

10 RXO1+ LVDS ODD 1 + Signal

11 RXO2- LVDS ODD 2 - Signal

12 RXO2+ LVDS ODD 2 + Signal

13 GND Ground

14 GND Ground

15 RXOC- LVDS ODD Clock - Signal

16 RXOC+ LVDS ODD Clock + Signal

17 RXO3- LVDS ODD 3 - Signal

18 RXO3+ LVDS ODD 3 + Signal

19 RXE0- LVDS EVEN 0 - Signal

20 RXE0+ LVDS EVEN 0 + Signal

21 RXE1- LVDS EVEN 1 - Signal

22 RXE1+ LVDS EVEN 1 + Signal

23 RXE2- LVDS EVEN 2 - Signal

24 RXE2+ LVDS EVEN 2 + Signal

25 GND Ground

26 GND Ground

27 RXEC- LVDS EVEN Clock - Signal

28 RXEC+ LVDS EVEN Clock + Signal

29 RXE3- LVDS EVEN 3 - Signal

30 RXE3+ LVDS EVEN 3 + Signal

Picture of bottom side of some controller, in this case,

signals ODD RXO are marked as BTX and signals EVEN RXE are as ATX , pairs numbers and power plus and minus are the same

In some boards, pin 3 and/or 4 are not connected at all, so always check specification of particular controller.

For example, lot of LCD screens with resolution 1024x768 or 1280x800 use only signals ODD0, ODD1, ODD2, ODD Clock, so only 4 pairs (8 wires) for LVDS transmission, plus GND and LCD Vcc (power supply). Rest are not used, this is 1 channel 6 bit connection type.

For example some 1280x1024 use ODD 0, ODD1, ODD2, ODD Clock, ODD3, Vcc and GND, what means 1 channel 8 bit .

For example some 1280x1024 or 1680x1050 monitor's 30 pins screens use ODD1, ODD1, ODD2, ODD Clock, ODD3, EVEN0, EVEN1, EVEN2, EVEN Clock, EVEN3, VCC and GND. This is 2 channel 8 bit transmission.

I got questions about particular firmware names, ex. what DO6L means ?

SI -single or DO -double channel

6 or 8 bits color depth

L -LVDS connection type

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So, now is most difficult and time consuming part of work, connection of original LVDS cable from laptop (or monitor), to LVDS socket, used on universal LCD controller board.

For cable work, I bought some sockets, pins 16, 20 and 32(only those are available) to made my own cables and see which one will be the best:

If you have an electronics parts shop far away, you can use old laptop's board with ATA (HDD2.5'') HDD connector .

This HDD connector is ideal for cable work, for LVDS connection to controller.