bedtime
Posts: 97
Joined: Thu Dec 13, 2018 6:02 pm

How to switch initial brightness?

Fri Jun 18, 2021 2:46 pm

Is there away that the brightness of the screen can be changed earlier in the boot process? I'd like to lower the brightness or even have the screen off until it is fully booted.

jamesh
Raspberry Pi Engineer & Forum Moderator
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Re: How to switch initial brightness?

Fri Jun 18, 2021 2:53 pm

Not that I can think of.
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gordon77
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Re: How to switch initial brightness?

Fri Jun 18, 2021 3:29 pm

How is the brightness controlled ?

If you can control it with a gpio could you use one that if off at boot ?

jamesh
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Re: How to switch initial brightness?

Fri Jun 18, 2021 4:23 pm

No, it's controlled from a I2C message to the display board on the screen, via the firmware and some mailboxes.

If you are using KMS (unlikely) then you could mod the driver to start up with 0 brightness.
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gordon77
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Re: How to switch initial brightness?

Fri Jun 18, 2021 4:39 pm

My mistake , l missed it was a pi official display.

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DougieLawson
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Re: How to switch initial brightness?

Fri Jun 18, 2021 5:48 pm

gordon77 wrote:
Fri Jun 18, 2021 3:29 pm
How is the brightness controlled ?
You write a brightness value (0 to 255) to /sys/class/backlight/rpi_backlight/brightness. You can do that with a sudo echo command or with something like my code at https://github.com/DougieLawson/backlight_dimmer
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