PiAutoDim

Auto-Dimming for the Raspberry-Pi 7" Touchscreen LCD Display

What?

Code and schematic diagram to automatically dim the backlight of the Raspberry-Pi Official 7" Touchscreen LCD display. Based on this light-sensor example from GPIO Zero.

Why?

1. I don't want to be blinded by the bright LCD backlight at night
2. Provide dynamic display brightness adjustment for optimal display contrast in all lighting conditions

Where?

On my nightstand, but you can see how it works at this demo link

Changelog

• v0.1 - Initial release

Hardware Setup

Parts needed:

• Cds photo cell / photoresistor (photo transistor OK)
• 10µF 16V capacitor (if using 1µF, edit charge_time_limit argument in autobrightness.py so that the charge_time_limit=0.01)
• Female jumper wires

Connection diagram:

Software Setup

Edit the backlight permissions file to allow read and write permissions to all users:

sudo nano /etc/udev/rules.d/backlight-permissions.rules

Insert:

SUBSYSTEM=="backlight",RUN+="/bin/chmod 666 /sys/class/backlight/%k/brightness /sys/class/backlight/%k/bl_power"

Put autobrightness.py on your pi, in a directory called PiAutoDim:

git clone https://github.com/dandydanny/PiAutoDim.git

Enable autorun of autobrightness.py on boot, by making it a systemd service

In /etc/systemd/system/, make a autobrightness.service file.

touch autobrightness.service

Open this file in an editor:

sudo nano autobrightness.service

Put in following:

[Unit]
Description=Get auto brightness service running at boot
After=mosquitto.service mysql.service

[Service]
ExecStart=/usr/bin/python3 /home/pi/PiAutoDim/autobrightness.py
Restart=always
StandardOutput=syslog
StandardError=syslog
SyslogIdentifier=autobrightness
User=pi
Group=pi

[Install]
WantedBy=multi-user.target

Press CTRL-O to save, and CTRL-X to exit nano editor.

Enable service to run on startup:

sudo systemctl enable autobrightness.service

Start autobrightness service (for current boot):

sudo systemctl start autobrightness.service

Check if it's running:

systemctl status autobrightness.service

Adjust the amount of light falling on the Cds sensor. The backlight level should change accordingly.

License

MIT

About

Daniel is a web developer seeking opportunities, beverage socials, and late-night taco runs. dandydanny.github.io