How to control the backlight brightness with PWM(7-B/7-C)
This method is only available for 7-B Rev3.2, 7-C Rev3.3 or above
Connect the Raspberry Pi：
In Raspberry Pi 3B/3B+, The backlight brightness can be controlled by following the command：
gpio -g pwm 18 1024 gpio -g mode 18 pwm gpio pwmc 1000 gpio -g pwm 18 X
（The value of X should be between 0 and 1024, 0 brightest， 1024 darkest）
In Raspberry Pi 4B, you need to update the wiringPi GPIO library (Raspberry Pi needs to connect to the Internet)：
cd /tmp wget https://project-downloads.drogon.net/wiringpi-latest.deb sudo dpkg -i -B wiringpi-latest.deb
Execute the following command to control the backlight brightness：
gpio -g pwm 18 1024 gpio -g mode 18 pwm gpio pwmc 1000 gpio -g pwm 18 X
（The value of X should be between 0 and 1024, 0 brightest， 1024 darkest）
