My brightness slider only goes down to '1' (just like my other paperwhites). You need to be in a really dark room (or have the front bezel off) to see the difference.
I just did some poking around in my PW3 over usbnet. I found this:
PHP Code:
echo 0 > /chroot/sys/devices/platform/imx-i2c.0/i2c-0/0-003c/max77696-bl.0/backlight/max77696-bl/brightness
Other numbers are brighter, but '0' is off...
That should be easy to squeeze into a KUAL extension... Or perhaps up and down buttons, without that pesky (lower limit of '1').
You can also read that location to see the current brightness level. It says '1' after you run the brightness slider all the way down to minimum (i.e. "almost" off).
If nobody has posted a "Frontlight OFF" KUAL extension yet when I get back from my evening walk (and I still remember), I will whip up a KUAL extension to turn frontlight off. You can use the frontlight slider control to turn it back to other brightness levels.
Now that I know how to control the frontlight, it is time to see how fast I can toggle it, and if it is fast enough for PWM optical sound output.
EDIT: See post below for "shorter path" version, with examples for MAX, MIN, and OFF brightness values: https://www.mobileread.com/forums/sho...03#post3323903