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I'm using a 3.5 inch SPI screen on a Raspberry PI3.

I would like to know how is it possible to control the backlight value with a shell command. I try to use the command echo %s > /sys/class/backlight/rpi_backlight/brightness but the rpi_backlight folder doesn't exist.

The OS is Raspbian Strech HW : RPi 3 B+ Display : http://www.lcdwiki.com/3.5inch_RPi_Display

Thanks, Jeff

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    I took a look at the link, it does not mention backlight, and pin 12 on seems to be used for something called "KEY1". Pin 12 (GPIO18) can be configured for PWM, which can be used to control backlight. I don't think it is possible with this screen, as they seem to use pin 12 for a key. Did you ask the supplier?
    – jogco
    Commented Mar 18, 2019 at 15:57
  • the "key" might just be a plugged hole in the plug .... that prevents incorrect insertion of a connector
    – jsotola
    Commented Mar 19, 2019 at 3:54

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After reading the XPT2046 datasheet and seeing the PCB, I found the same conclusion as JOGCO. The backlight is not software manageable.

To find an other way, I need to make destructive test on the display.

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