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Control the backlight on the official RPF display based on a touch event.
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README.md

Backlight dimmer

Leaving the backlight on the Official Raspberry Pi touchscreen can quickly wear it out. If you have a use that requires the pi to be on all the time, but does not require the display on all the time, then turning off the backlight while not in use can dramatically increase the life of the backlight.

Backlight dimmer will transparently dim the display backlight after there has been no input for a specifed timeout, independent of anything using the display at the moment. It will then turn the touchscreen back on when input is received. The timeout period is set by a command-line argument.

Note: This does not stop the event from getting to whatever is running on the display. Whatever is running will still receive an event, even if the display is off.

The program will use a linux event device like /dev/input/event0 to receive events from the touchscreen, keyboard, mouse, etc., and /sys/class/backlight/rpi-backlight/brightness to dim the backlight. The event device is a command-line parameter without the /dev/input/ path specification.

Installation

Clone the repository and change directories:

git clone https://github.com/DougieLawson/backlight_dimmer
cd backlight_dimmer

Build and run it!

make
sudo setuid  ./timeout
./timeout 10 event0

Multiple devices may be specified.

Note: It must be run as root or with sudo to be able to access the backlight. Or you can make the program setuid and owned by root It can be run at startup, for example by putting a line in /etc/rc.local

Conflict with console blanker

When running this program without X Windows running, such as when running a Kivy program in the console at startup, you may run into a conflict with a console blanker. In such an instance, the backlight will be turned on, but with the console blanked, it seems like the backlight has not come on.

In this case, follow one of these methods for disabling the console blanker:

  • Raspbian Jessie : Add the following line to /etc/rc.local (on the line before the final exit 0) and reboot:
  sh -c "TERM=linux setterm -blank 0 >/dev/tty0"

Even though /dev/tty0 is used, this should propagate across all terminals.

  • Raspbian Wheezy : Edit /etc/kbd/config and change the values for the variable shown below, then reboot:
  BLANK_TIME=0

© Copyright 2019, Dougie Lawson, all rights reserved.

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