2019-12-29, 04:17 PM
Following up on my own question in http://forum.openmarine.net/showthread.php?tid=2174 here's how I'm currently controlling the backlight on the official Raspberry Pi Foundation 7" touchscreen (v1.1) via xscreensaver.
It's not the perfect solution, but close enough for now. I'm still looking into whether I can make this into a proper xscreensaver module that can be distributed as a single file.
Using a script I found and edited, I launch a process to watch xscreensaver and toggle the backlight when xscreensaver blanks and unblanks the display. This means if you install the xscreensaver package, you can configure the screen blanking time from the GUI, turn it on or off entirely, and the RPi display backlight will respond to those changes. The process starts automatically on boot.
I'll write down the entire installation procedure in case anyone wants to try it out.
To install xscreensaver, do
Edit a new file, I'll call it backlight_control.sh. I use nano:
Input the following
Save the file. Now to make the script executable
To launch the script as a process automatically on reboot, edit this file:
Add the following line. Make sure it's below the line that reads "@xscreensaver -no-splash"; xscreensaver-command needs to be started after xscreensaver.
The '&' makes sure the script can exit, leaving the new process running in the background. Save the file and reboot your Pi.
The backlight should turn off when the screensaver blanks the screen, and turn back on upon keyboard, mouse or touch input.
If anyone has any suggestions on how to improve this or a better solution, feel free to pitch in.
Some notes:
Fair winds,
Andy
It's not the perfect solution, but close enough for now. I'm still looking into whether I can make this into a proper xscreensaver module that can be distributed as a single file.
Using a script I found and edited, I launch a process to watch xscreensaver and toggle the backlight when xscreensaver blanks and unblanks the display. This means if you install the xscreensaver package, you can configure the screen blanking time from the GUI, turn it on or off entirely, and the RPi display backlight will respond to those changes. The process starts automatically on boot.
I'll write down the entire installation procedure in case anyone wants to try it out.
To install xscreensaver, do
Code:
sudo apt-get install xscreensaverEdit a new file, I'll call it backlight_control.sh. I use nano:
Code:
nano ~/backlight_control.shInput the following
Code:
#!/bin/sh
process() {
while read line; do
case "$line" in
UNBLANK*)
sh -c 'echo "0" > /sys/class/backlight/rpi_backlight/bl_power'
;;
BLANK*)
sh -c 'echo "1" > /sys/class/backlight/rpi_backlight/bl_power'
;;
esac
done
}
xscreensaver-command -watch | processSave the file. Now to make the script executable
Code:
chmod +x ~/backlight_control.shTo launch the script as a process automatically on reboot, edit this file:
Code:
sudo nano /etc/xdg/lxsession/LXDE-pi/autostartAdd the following line. Make sure it's below the line that reads "@xscreensaver -no-splash"; xscreensaver-command needs to be started after xscreensaver.
Code:
@sudo /home/pi/backlight_control.sh &The '&' makes sure the script can exit, leaving the new process running in the background. Save the file and reboot your Pi.
The backlight should turn off when the screensaver blanks the screen, and turn back on upon keyboard, mouse or touch input.
If anyone has any suggestions on how to improve this or a better solution, feel free to pitch in.
Some notes:
- I don't think you need to have the entire xscreensaver package installed for this, as long as you just want the default screen blanking functionality, but I haven't tested this without it.
- There are more messages that xscreensaver sends out (specifically LOCK and RUN). Adding cases to the script can handle those too. I haven't looked more closely at what they do, but they might provide interesting functionality.
Fair winds,
Andy