DavidInvenio
Posts: 9
Joined: Wed Mar 07, 2018 10:20 pm

Why does Raspbian NOT HAVE /sys/class/backlight/rpi-backlight/bl_power???

Wed Mar 14, 2018 12:56 am

I have found MANY MANY posts that reference this file and it's parent folder to turn off the backlight.
SADLY - My raspbian doesn't have that file nor parent folder.
And I have failed to find ANY reason by using Google or searching these forums.

Can anyone explain???

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DougieLawson
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Re: Why does Raspbian NOT HAVE /sys/class/backlight/rpi-backlight/bl_power???

Wed Mar 14, 2018 1:17 am

It exists on my RPi that has the "official" RPF 7" touch screen.

Code: Select all

[email protected]:/sys/class/backlight $ ls -la rpi_backlight
lrwxrwxrwx 1 root root 0 Mar 13 21:17 rpi_backlight -> ../../devices/platform/rpi_backlight/backlight/rpi_backlight
[email protected]:/sys/class/backlight $ cd rpi_backlight
[email protected]:/sys/class/backlight/rpi_backlight $ ls -la
total 0
drwxr-xr-x 3 root root    0 Mar 13 21:17 .
drwxr-xr-x 3 root root    0 Mar 13 21:17 ..
-r--r--r-- 1 root root 4096 Mar 14 01:16 actual_brightness
-rw-r--r-- 1 root root 4096 Mar 14 01:16 bl_power
-rw-r--r-- 1 root root 4096 Mar 13 21:17 brightness
lrwxrwxrwx 1 root root    0 Mar 14 01:16 device -> ../../../rpi_backlight
-r--r--r-- 1 root root 4096 Mar 13 21:17 max_brightness
drwxr-xr-x 2 root root    0 Mar 14 01:16 power
lrwxrwxrwx 1 root root    0 Mar 13 21:17 subsystem -> ../../../../../class/backlight
-r--r--r-- 1 root root 4096 Mar 13 21:17 type
-rw-r--r-- 1 root root 4096 Mar 13 21:17 uevent
[email protected]:/sys/class/backlight/rpi_backlight $
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DavidInvenio
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Joined: Wed Mar 07, 2018 10:20 pm

Re: Why does Raspbian NOT HAVE /sys/class/backlight/rpi-backlight/bl_power???

Fri Mar 16, 2018 11:14 pm

Here is the information about my LCD

3.5inch RPi LCD (A), 320×480
SKU: 9904
Part Number: 3.5inch RPi LCD (A)
Brand: Waveshare


LCD Type TFT
LCD Interface SPI
Touch Screen Type Resistive
Touch Screen Controller XPT2046
Colors 65536
Backlight LED
Resolution 320*480 (Pixel)
Aspect Ratio 8:5
Power Consumption TBD
Backlight Current TBD
Operating Temp. (℃) TBD

I am using Raspbian (Jessie)

My /sys/class/backlight has NO files and NO folders.

Can anyone offer any advice?

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DougieLawson
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Re: Why does Raspbian NOT HAVE /sys/class/backlight/rpi-backlight/bl_power???

Fri Mar 16, 2018 11:17 pm

Build a fresh SDCard with Raspbian 2018-03-13 or NOOBS 2.7 and boot that.
Microprocessor, Raspberry Pi & Arduino Hacker
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DavidInvenio
Posts: 9
Joined: Wed Mar 07, 2018 10:20 pm

Re: Why does Raspbian NOT HAVE /sys/class/backlight/rpi-backlight/bl_power???

Sat Mar 17, 2018 12:04 am

THANK YOU - great suggestion! I am doing just that!

I'm also going to burn THIS image to an SD chip - as this seems to have the Waveshare driver loaded on Raspbian already. It appears to be less than a year since the last update, not sure how old the image itself is, but worth a try.

Thanks again!
/D

DavidInvenio
Posts: 9
Joined: Wed Mar 07, 2018 10:20 pm

Re: Why does Raspbian NOT HAVE /sys/class/backlight/rpi-backlight/bl_power???

Sat Mar 17, 2018 3:10 am

Ok - I have install NOOBs - as well as the Waveshare img that included the driver for Jessie.
/sys/class/backlight remains completely empty.

This is the kinda thing I expect in the Windows world LOL!

I have no idea what to try next, but I'm frustrated beyond words!

Any other advice would be so greatly welcome - that is also beyond words! :-)

jamesh
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Re: Why does Raspbian NOT HAVE /sys/class/backlight/rpi-backlight/bl_power???

Sat Mar 17, 2018 7:38 am

That's a deficiency in the driver for your particular device I think, so I guess you need to talk to your supplier about it or fix the driver yourself.
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PiGraham
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Re: Why does Raspbian NOT HAVE /sys/class/backlight/rpi-backlight/bl_power???

Sat Mar 17, 2018 9:16 am

DavidInvenio wrote:
Sat Mar 17, 2018 3:10 am
Ok - I have install NOOBs - as well as the Waveshare img that included the driver for Jessie.
/sys/class/backlight remains completely empty.

This is the kinda thing I expect in the Windows world LOL!

I have no idea what to try next, but I'm frustrated beyond words!

Any other advice would be so greatly welcome - that is also beyond words! :-)
I don't think the display you have provides any backlight control.
The 5 inch HDMI version has a switch to turn backlight on or off, but no software control of brightness. That can be modified to allow software control. See here
viewtopic.php?t=126321
Nothing like that seems to be on the 3.5 inch SPI interfaced model.
If you want backlight control get a display with controllable backlight and check that any driver you will use supports BL control.

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