Backlight issue fix?

[fsflover]

There is finally a new section in the wiki concerning Pinephone hardware edition 1.2a (postmarketOS CE). It says that two backlight issues are still present in 1.2a; the second one will probably be fixed in the Manjaro CE version. However, nothing is said about the first one. This is a pretty serious issue: it makes Pinephone barely usable in very low lightning conditions due to the blinking of its backlight. Are there plans to fix it for the Manjaro CE?

[hamilton]

Would like to know too.

[fsflover]

There is now a section in the wiki Pinephone hardware edition 1.2b (Manjaro CE).

It seems the main backlight issue has not been fixed. Bad news. Thinking about cancelling my order of Manjaro...

[User 18618]

I'd love to take advantage of the discounted 1.2b board, but I'm put off by the backlight issue as well

[bcnaz]

In actual use, in dark rooms I have not noticed any problems with the screen.

[User 18618]

@bcnaz I believe the issues is twofold: how "low" the brightness can go, and PWM strobing.

[megous]

@bcnaz I believe the issues is twofold: how "low" the brightness can go, and PWM strobing.

PWM is only used to generate reference voltage for the stable current source. Backlight brightness is not done by PWM strobing of the backlight LEDs themselves.

Unfortunately the reference voltage for PWM GPIO pin is not completely stable. Any variation in that voltage is quite visible on the LED bightness, especially since at low brightness backlight LEDs are operating in the knee of their V-I characteristic, and are very sensitive to any change in current of the constant current source regulated by that PWM.

The further away from the knee, the less this is an issue.

[User 18618]

Thanks for the clarification @megous

[fsflover]

@megous commented on that:

I'm not aware of any effort to fix that. It's already reasonably non-flickery thanks to other fixes, since that paragraph was written.