[HOWTO] change LCD brightness

Started by codifies, March 06, 2014, 03:50:54 PM

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In theory there should be a way to change brightness via the LCD module but I couldn't suss it out... for better or worse here is how I change brightness...

first of all be sure to follow the instructions here

check /proc/config.gz before rushing off to recompile a kernel you might already have it (sunxi pwm)...

(add pwm-sunxi to /etc/modules for good measure !)

in addition in script.bin make sure you have changed these settings (like this)

lcd_pwm_not_used = 1
lcd_pwm_used = 0

in the first LCD stanza

it might just be a good idea to have something connected to the debug serial port in case anything goes wrong ;)

once rebooted you should see something in /sys/ like this /sys/class/pwm-sunxi/pwm0

that being the case add to /etc/rc.local (before exti 0!)

echo "40" > /sys/class/pwm-sunxi/pwm0/duty_percent

now when you boot your backlight should be at 40%... (time to test the LiPo again me thinks!)

the lowest I could go was 25% anything lower seems to blank the display, its not impossible that messing with the duty frequency you could go lower, but 25% is so dim its basically pointless...

btw you cant sudo echo as the pipe wont inherit root, I seem to remember there is some FU with tee to get round this, of course you can sudo su for a quick while, because you're really not dim enough to be running as root all the time now are you...


It might be interesting I post an update for controlling the LCD Brightness on the newer mainline kernel images - Debian 11 Bullseye.

Tested under XFCE desktop environment.

The brightness can be controlled by setting value in range from 1 to 10 in /sys/class/backlight/backlight/brightness.

For the complete standby of the display I disabled xfce4 power manager and used xset dpms.

# Disable xfce power-manager monitor control
xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/blank-on-ac -s 0
xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/dpms-on-ac-sleep -s 0
xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/dpms-on-ac-off -s 0
xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/dpms-enabled -s false
# Using xset dpms
xset dpms force on


# Turn off display
COUNT=$(cat /sys/class/backlight/backlight/brightness)
while [ $COUNT -gt 1 ]; do
  COUNT=$(($COUNT - 1))
  echo $COUNT > /sys/class/backlight/backlight/brightness
  sleep 0.1

# USING xset dpms to turn off the monitor
xset dpms force off

Kernel 3.4 Image LCD standby code:

# Turn off display
COUNT=$(cat /sys/class/pwm-sunxi/pwm0/duty_percent)
while [ $COUNT -gt 20 ]; do
  COUNT=$(($COUNT - 5))
  echo $COUNT > /sys/class/pwm-sunxi/pwm0/duty_percent
  sleep 0.1

# LCD power GPIO disable
echo 0 > /sys/class/gpio/gpio58_ph8/value # GPIO might be manually added if missing
# echo 0 > /sys/class/gpio/gpio232/value # mainline GPIO