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PiTFT 2.8 Backlight trouble
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PiTFT 2.8 Backlight trouble

by prupert on Sun Feb 11, 2018 6:50 pm

Hi

I've successfully got my 2.8 PiTFT working on my early revision Pi 1 Model B (the one with 256MB memory and a 20 pin header).

However, I really can't master the backlight control (I'd like to lower the brightness, but not turn the screen off entirely). Following the instructions here: https://learn.adafruit.com/adafruit-pit ... ht-control I can turn on and off the backlight via:

sudo sh -c 'echo "0" > /sys/class/backlight/soc\:backlight/brightness'
and
sudo sh -c 'echo "1" > /sys/class/backlight/soc\:backlight/brightness'

But none of the commands using gpio 18 work for me. Running ls -l /sys/class/gpio, I get:
total 0
-rwxrwx--- 1 root gpio 4096 Feb 11 22:33 export
lrwxrwxrwx 1 root gpio 0 Feb 11 22:31 gpiochip0 -> ../../devices/platform/soc/20200000.gpio/gpio/gpiochip0
lrwxrwxrwx 1 root gpio 0 Feb 11 22:31 gpiochip506 -> ../../devices/platform/soc/20204000.spi/spi_master/spi0/spi0.1/stmpe-gpio/gpio/gpiochip506
-rwxrwx--- 1 root gpio 4096 Feb 11 22:31 unexport

I feel I also need a gpiochip508 entry here but I don't have this. Doing sudo sh -c "echo 508 > /sys/class/gpio/export", I get an IO error.

I've definitely got the resistance version, not the capacitive version, since the image showing the bit you need to solder doesn't match mine and I can see STMPE610 printed on my board.

Any idea what I can do to get more control over the brightness?

prupert
 
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Joined: Sun Feb 11, 2018 6:36 pm

Please be positive and constructive with your questions and comments.