chris25nj
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TFT LCD DRIVER for 8" LCD

Wed Jun 09, 2021 11:19 pm

Hello all, I am new to RPi and am working on a project where I want to use an LCD touch screen that I recovered from another device. I am struggling to figure out how to know which driver board I need to connect it to the RPi. I have the model number of the LCD which is LB080WV3-B1. I also was able to find the specifications of the panel from the manufacture which is located here: https://datasheetspdf.com/pdf/721772/LG/LB080WV3-B1/1

I don't know what I am supposed to be looking for on the spec sheet to tell me which controller driver I can use. I have done a bunch of googling to try and figure it out but am more confused now than when I started. Can anyone offer any guidance or explain how to find the LCD controller that I need?

Thanks in advance for any assistance!! :)

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Gavinmc42
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Re: TFT LCD DRIVER for 8" LCD

Thu Jun 10, 2021 4:09 am

Does the 40way pinout match this one?
https://www.adafruit.com/product/2219
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chris25nj
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Re: TFT LCD DRIVER for 8" LCD

Thu Jun 10, 2021 4:29 am

I saw that one but how do I know if it is a match? I'm not sure I understand how I would answer your question?

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Gavinmc42
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Re: TFT LCD DRIVER for 8" LCD

Thu Jun 10, 2021 4:32 am

Pin1 on that PCB connector must have the same name/specs as the LCD display pin 1.
All 40 pins must match.

If not then you need to make an adapter to swap pins around.
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aBUGSworstnightmare
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Re: TFT LCD DRIVER for 8" LCD

Thu Jun 10, 2021 5:06 am

chris25nj wrote:
Wed Jun 09, 2021 11:19 pm
Hello all, I am new to RPi and am working on a project where I want to use an LCD touch screen that I recovered from another device. I am struggling to figure out how to know which driver board I need to connect it to the RPi. I have the model number of the LCD which is LB080WV3-B1. I also was able to find the specifications of the panel from the manufacture which is located here: https://datasheetspdf.com/pdf/721772/LG/LB080WV3-B1/1

I don't know what I am supposed to be looking for on the spec sheet to tell me which controller driver I can use. I have done a bunch of googling to try and figure it out but am more confused now than when I started. Can anyone offer any guidance or explain how to find the LCD controller that I need?

Thanks in advance for any assistance!! :)
page 5 of the spec tells you this module has an 18-bit RGB interface on 40pin FFC.
As it is an RGB interface you can directly connect it to the Raspberry DPI interface (https://www.raspberrypi.org/documentati ... /README.md) without 'glue logic'.So, what you will need is an adapter board which converts the 40pin GPIO (2.54mm pitch) interface to 0.5mm FFC. In addition you will need to input the timing (page 10) to let the RPI now how to drive the display.

The simplest adapter is this one https://www.adafruit.com/product/1492, use jump wires to connect to 40pin GPIO.

Before you start: do you have the backlight inverter as well? Be carefull and dont touch the coil/other components --> high voltage.
Fire up the BL before you spend any money on the display. CCFL lamps tend to fail if they have not been switched on frequently.

Bellow is an example of a more compact solution:
IMG_20210109_152315.jpg
Dedicated version of the board for a particular display. Backlight LED driver and WiFi controls are assembled on the board as the full 24-bit DPI interface is used
IMG_20210109_152315.jpg (192.47 KiB) Viewed 580 times
IMG_20210610_071012.jpg
Universal version of a DPI display interface - beta as the board should have a possibility for using external power (3.3V supply rail on the RPI not able to cope with the TFT matrix inrush current of the 5.6in Innolux display connected to the board)
IMG_20210610_071012.jpg (91.58 KiB) Viewed 580 times
IMG_20210610_071034.jpg
bottom of the PCB. 18-bit DPI only, no BL driver needed as this is available on the TFT. The small PCB converts the 'universal' pinout of the 54-pin FPC to the one required by the display.
IMG_20210610_071034.jpg (146.22 KiB) Viewed 580 times
Last edited by aBUGSworstnightmare on Thu Jun 10, 2021 5:49 am, edited 1 time in total.

aBUGSworstnightmare
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Re: TFT LCD DRIVER for 8" LCD

Thu Jun 10, 2021 5:47 am

This is what the above setup looks like 'in action'. That 5.6in display is 640x480pixels native resolution. I'm running KMS graphics driver which allows me to scale my desktop to 1024x768pixels which still has a good readability on the display (xrandr --output DPI-1 --primary --scale 1.6x1.6)
IMG_20210610_073853.jpg
5.6in display connected to DPI interface
IMG_20210610_073853.jpg (145.7 KiB) Viewed 577 times
The pictures below show you the effect of the '--scale' option:
IMG_20210610_075138.jpg
desktop is scaled to 1024x768 pixels resolution
IMG_20210610_075138.jpg (149.39 KiB) Viewed 563 times
IMG_20210610_075201.jpg
desktop is unscaled -> 640x480pixels resolution
IMG_20210610_075201.jpg (129.28 KiB) Viewed 563 times

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Gavinmc42
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Re: TFT LCD DRIVER for 8" LCD

Thu Jun 10, 2021 6:39 am

What's the video playback like on the 640x480?
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aBUGSworstnightmare
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Re: TFT LCD DRIVER for 8" LCD

Thu Jun 10, 2021 6:56 am

Gavinmc42 wrote:
Thu Jun 10, 2021 6:39 am
What's the video playback like on the 640x480?
sorry, can you be more precise on your question? Do you want to know what video playback looks like on VGA resolution using VLC?

chris25nj
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Re: TFT LCD DRIVER for 8" LCD

Thu Jun 10, 2021 11:16 pm

aBUGSworstnightmare wrote:
Thu Jun 10, 2021 5:06 am
Before you start: do you have the backlight inverter as well?
[/quote]

Thank you sooooo much for the detailed explanation!!!!! One follow up question, not sure what you mean by the "backlight inverter". The LCD has another two channel (red/black) wire sticking out of it that I am assuming is the power cable for the backlight. Is that what you are referring to? If yes, where is that supposed to be connected to on the RPI? or do I just need to connect it to an external power supply?

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Gavinmc42
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Re: TFT LCD DRIVER for 8" LCD

Fri Jun 11, 2021 2:01 am

Do you want to know what video playback looks like on VGA resolution using VLC
Are the fps watchable?
I was under the impression DPI 320 x 240 was ok, 480 x 320 was not so good and 640 x 480 would be annoying.
Hmm, maybe that was SPI LCDs.

Might have to get some of the DPI types and try them.
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aBUGSworstnightmare
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Re: TFT LCD DRIVER for 8" LCD

Fri Jun 11, 2021 4:27 am

Gavinmc42 wrote:
Fri Jun 11, 2021 2:01 am
Do you want to know what video playback looks like on VGA resolution using VLC
Are the fps watchable?
I was under the impression DPI 320 x 240 was ok, 480 x 320 was not so good and 640 x 480 would be annoying.
Hmm, maybe that was SPI LCDs.

Might have to get some of the DPI types and try them.
FPS is 60Hz. I assume you got issues with higher resolution SPI displays.

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Gavinmc42
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Re: TFT LCD DRIVER for 8" LCD

Fri Jun 11, 2021 5:08 am

I assume you got issues with higher resolution SPI displays.
I want to do bare metal and SPI is a bit slow and drivers are only for Linux.
DPI use lots of GPIO pins.

But DPI might be ok for CM4 based tablet use.
HDMI is an extra chip, which uses more power and is not as compact.

Been wondering what is the max DPI LCD that is usable
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aBUGSworstnightmare
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Re: TFT LCD DRIVER for 8" LCD

Fri Jun 11, 2021 6:45 pm

Used Full-HD on DPI without issues already.
For sure SPI is slow hat higher resolution/frame rate as a lot of data needs to be send.
Use MIPI instead if you need GPIO

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Gavinmc42
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Re: TFT LCD DRIVER for 8" LCD

Sat Jun 12, 2021 1:01 am

Use MIPI instead if you need GPIO
Got the 7" official display, but even that has an adaptor interface chip and the RPT guys say that is about the max resolution.

Would be nice if there is a MIPI display that just plugs in.
Maybe one day.

In the mean time HDMI is the easiest and are down to 3.5" now.
More DPI would be nice but makers tend to value add and use SPI driven interfaces.
Slows the clones makers because they require drivers?

Now the CM4 is out and it is pretty good time to revisit the DPI interface.
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aBUGSworstnightmare
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Re: TFT LCD DRIVER for 8" LCD

Sat Jun 12, 2021 5:30 am

Gavinmc42 wrote:
Sat Jun 12, 2021 1:01 am
Use MIPI instead if you need GPIO
Got the 7" official display, but even that has an adaptor interface chip and the RPT guys say that is about the max resolution.

Would be nice if there is a MIPI display that just plugs in.
Maybe one day.
sorry man, but you're wrong!
On 2-lane MIPI you can run 1280x800 pixels with ease, 3-lane is just enough (but tight) for 1920x1080pixels and 4-lane, well depends what you can get.
The standard PI only exposes 2-lane DSI, that's what the 'limit' comes from!

This is a 7in with 1280x800 pixels running happily (finally now) via MIPI interface from a CM4 (tested with 2- and 3-lane config, 4-lane would be nice for lowest EMI but fails)
Image

for using MIPI with any display of your choice (or via a bridge chip like above) you need to use KMS and have a driver for your display in place.
Search the forum and you will find more info on this topic.

Note: DSI to RGB chip used on the RPI display is EOL; so there is the chance that we will see a new official display in the future (but also a risk that RPi decided to make a last-time-buy with huge quantaties in orderto be able to ship longer).

And sorry, but there is no value add in SPI other than making the interface more compact.
Last edited by aBUGSworstnightmare on Sat Jun 12, 2021 5:51 am, edited 1 time in total.

aBUGSworstnightmare
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Re: TFT LCD DRIVER for 8" LCD

Sat Jun 12, 2021 5:51 am

chris25nj wrote:
Thu Jun 10, 2021 11:16 pm
Thank you sooooo much for the detailed explanation!!!!! One follow up question, not sure what you mean by the "backlight inverter". The LCD has another two channel (red/black) wire sticking out of it that I am assuming is the power cable for the backlight. Is that what you are referring to? If yes, where is that supposed to be connected to on the RPI? or do I just need to connect it to an external power supply?
this additional connector is the input to the CCFL backlight lamp. CCFL require high voltage to operate and the device which is used to drive them is usually called an inverter. Below is an example picture:
Image
if you did not/been unable to salvage that component from your display donar device you need to find a new one (extra costs, different specs, ..). And..there is still the risk the backlight fails on first start attempt!

Look at table 2 of your display spec: Power input to that connector is 630Vrms @ 6mArms (!) typ. Caution: risk of electrical shock!
You can't drive the backlight from your Pi!

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Gavinmc42
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Re: TFT LCD DRIVER for 8" LCD

Sat Jun 12, 2021 7:53 am

On 2-lane MIPI you can run 1280x800 pixels with ease,
Good to know, maybe the Official 7" was at that converter chips limit?

It would be nice if there was a RPF DSI display that has no separate PCB.
I want a CM4 tablet.

If that chip is EOL then we can probably assume RPT have displays on their todo list.

So drivers for DPI or MIPI, which one is easier?
I will be doing baremetal.

But I am still hanging out for a daylight visible screen.
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aBUGSworstnightmare
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Re: TFT LCD DRIVER for 8" LCD

Sat Jun 12, 2021 10:20 am

Sorry, no idea on baremetal!
Simplest use of a DPI display is by adding the timing to `panel-simple.c', write an overlay which uses it, compile everything and then add the overlay to config.txt. No need to write any driver.

MIPI display will require a driver, to be developed either by using an existing one as template, or from scratch. Way more complicated!

'Daylight readable' displays exist.. You only need to find them. Sorry, but will not answer any questions to the one shown below.!
PSX_20210612_121204.jpg
No backlight at all; reflective TFT, 5in size
PSX_20210612_121204.jpg (120.06 KiB) Viewed 257 times

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Gavinmc42
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Re: TFT LCD DRIVER for 8" LCD

Sat Jun 12, 2021 10:43 am

Digikey have a 4.4" 640 x 480 and 320 x 240 front lite reflective ones in stock.
Azumo front light technology, very low power.
Display LPM044M141A etc but it is SPI which might be ok for eReader and outdoor mapping.

Already have a 4" HDMI 800x480, it's a bit bulky - looking for something bigger in the 7-9" range.

Baremetal not so hard if you use Ultibo, but lack of LCD schematics/drivers is a pain.
Not hard to do, just takes time and they are simpler than doing Linux drivers.

Nice 5" display.
Saw some flip phone prototypes LCDs nearly 20years ago, fantastic in the sun, too expensive :(
Not sure why the tech is being held back.
Trying to keep everyone inside?
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