LCD backlight.

Started by arjepsen, April 29, 2021, 02:29:46 am

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I'm working on getting the controller of my beer machine set up.
It's an A13-SOM that is connected to some proprietary board, which has an LCD with a capacitive touch panel attached.
I'm using the latest Focal image I found on

The panel does work. However, the backlight isn't on at boot, and I have to manually enable it using these commands:
echo 35 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio35/direction
echo 5 > /sys/class/gpio/gpio35/value

So it's turned on by setting pin PB3 high.
I've played around with the panel and backlight parts in /sys/class, but so far I haven't been able to turn it on there.
I could put these commands ind a boot script, but I wonder if there's any way to do the same thing through a dts overlay?



For sure it is possible to add it in the overlay. You can use these overlays as a basis to create similar for the A13 board:

We haven't used capacitive touch screens with A13 boards (only resistive). It will require some hardware and software effort to get it working.
Technical support and documentation manager at Olimex


Thanks for your input.
The panel works - although I did spend a long time on getting the capacitive touch panel working (goodix gt911 chip). That part works now.
As mentioned, the display itself also works, but I would like to turn it on through a dts overlay, instead of having to do the "manual" gpio commands.
I did manage to get it to turn on, by adding a fragment part with
enable-gpios = <&pio 1 3 0>;However, the screen just lights up completely white, and stays that way...
So it seems like its turned on, but something isn't working the way it should.
If I do the three commands mentioned, I get the command prompt shown, and the panel works as it should.