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Does the touch panel work when the backlight is turned off?

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  • Does the touch panel work when the backlight is turned off?


    We are developing an industrial application and we wanted to switch off the display when it is not in use ( 99% of the time ) and turn it on again when it is requiered by touching the display but it seems it is not working.

    Just after turning off the backlight ( by echoing a 0 in /sys/class/backlight/4dpi/brightness ), if we press the display, it receives the pressure, but after a while, nothing appears to be received in the touch panel. ¿ Should the touch panel still be working after the brightness is set to 0 ? If not, is it there any solution so we can activate the display by pressing the touch panel?

    Thanks a lot


  • #2
    Hi Enrique,

    What particular display module for RPi are you using?

    Basically, the LCD display driver, backlight, and touch controller are connected directly to the RPI via the 20-pin header. This means that the RPi has the sole control over the backlight, LCD, and touch panel making all three independent.

    If the PWM on the backlight was set to zero then the display dims, but the touch panel should still be active. By the way, just a quick question on the test made. How did you determine/view the status/output of the touch controller while the backlight was turned off?


    • #3
      Thanks for your reply. The display I'm using is the 4DPi-32.

      The only test I did until now it is to place a huge button in the display to turn off/on the display, press it, so the backlight is turned off and press again to turn on the backlight again. If I press the display twice with few secons of difference between them, the display turns off and on, but if I press the display so I turn it off and I leave it for some minutes, it does not become "alive", but the rest of the RPi Works, other tasks in my program run perfectly and I can connect via ssh and other things.

      With your words, I will test the interrupt of the touch pad of the display.