rpi-auto-backlight

A Python service for automatically adjusting the brightness of the official Raspberry Pi 7" touch display based on the signal received from an external brightness sensor.

Requirements

• Raspberry PI
• LM393 light sensor ( I use this one )
• Python3

Installation

1. Clone the project repository

git clone https://github.com/dquercus/rpi-auto-backlight.git

2. Install python dependencies for the project

sudo apt-get install python3-pip python3-rpi.gpio
sudo pip3 install rpi-backlight

3. Create this udev rule to update permissions, otherwise you'll have to run the service as root:

echo 'SUBSYSTEM=="backlight",RUN+="/bin/chmod 666 /sys/class/backlight/%k/brightness /sys/class/backlight/%k/bl_power"' | sudo tee -a /etc/udev/rules.d/backlight-permissions.rules

4. Create service user with access to the GPIO ports

adduser --system --no-create-home autobacklight
sudo usermod -a -G gpio autobacklight

5. Deploy script and register service

cd rpi-auto-backlight
sudo cp rpi-auto-backlight-gpio.py /usr/local/bin/
sudo chmod +x /usr/local/bin/rpi-auto-backlight-gpio.py
sudo cp rpi-auto-backlight-gpio.service /etc/systemd/system/
sudo chmod 777 /etc/systemd/system/rpi-auto-backlight-gpio.service

6. Adjust and then copy configuration file /etc/auto_backlight.cfg

cd rpi-auto-backlight
sudo cp auto_backlight.cfg /etc/auto_backlight.cfg 

7. Enable service so its executed on boot

sudo systemctl daemon-reload
sudo systemctl enable rpi-auto-backlight-gpio.service

Configuration

The script supports the following configuration options via configuration file:

Variable	Description	Default value
RPI_PORT	GPIO port for light digital signal	7
DARK_BRIGHTNESS	Brightness level when no light detected	5
LIGHT_BRIGHTNESS	Brightness level when light detected	90
LOOP_PAUSE	Indicates how ofter the system checks for a new value in the GPIO port	2

Configuration file can by changed using system variable AUTO_BRIGHTNESS_CONFIG_FILE to point to a different path.

Acknowledgements

Thanks to torfsen/python-systemd-tutorial for the instructions for running a python script as daemon using systemd.