Contrast adjustment for LVDS display

Technical Support
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1

Hi,

I am using Apalis T30 SOMM module with Ixora V1.0A Carrier Board. I have interfaced 7" TFT LCD display using LVDS. The details of the LCD display is as below:

Resolution : 1024 x 600
Display Colors : 262K colors (RGB 6-bits)

I made the settings in the U-Boot command prompt as below:

setenv vidargs 'video=tegrafb0:1024x600-18@60 fbcon=map:1'
setenv lvds_setting 'gpio set 216;gpio set 222;gpio set 226;gpio set 225;gpio set 221;gpio set 220'
bootcmd=run lvds_setting;run emmcboot

Once the Linux kernel is booted, I executed the below commands,

/usr/bin/lvds-single-channel.sh
echo 0 > /sys/class/backlight/pwm-backlight/bl_power
echo 200 > /sys/class/backlight/pwm-backlight/brightness

With these settings, the display is up and I am able to see the LXDE Desktop environment. But, the contrast is not so good. I changed the brightness level but no improvement.

So, can I please get some help about how to change the contrast ratio.

I am attaching the snap shots of the display.

Thanks & Regards
Vijay H.S

2

Hi

Is there a reason why you do not set gpio 219 and 223 in your U-Boot ‘lvds_setting’ variable?

Could you post how the red, green and blue in the attached test pictures look like? Maybe the Farbbalken.png one could also be helpful.

Max

3

Hi Max,

Thanks for the reply. Sorry for my late response, actually I was busy with some other work.

BTW, regarding gpio 219 and 233, I am already using them in the /usr/bin/lvds-single-channel.sh and also I have now included them in the u-boot env (using setenv lvds_setting) but no improvement.

I am attaching the test pictures as requested by you.

Thanks & Regards
Vijay H.S
link text

4

As you do not reveal what exact display you are interfacing I suggest for you to try different settings of the LVDS configuration GPIOs as suggested in the following article on our developer website.

5

Hi Marcel,

I have already tried with the GPIO configurations and its not helping. Also, I am attaching the datasheet of the display we are using.

Thanks & Regards
Vijay H.S
link text

6

I could not find anything much suspicious in the display data sheet. Should really work quite straight forward. However what exactly did you set those display hardware configuration pins (e.g. CABCEN0, CABCEN1, RESET, SELB, STBYB) to?

Did you connect all 5 (4 data one clock) diff pairs properly?

How about the software resolution and timing configuration (e.g. did you use regular video=tegrafb0:1024x600-16@60)?

To rule out any hardware issues have you tried it with another set of carrier board, display and module as well?