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4DCAPE-70T dimmed (brightness)

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  • 4DCAPE-70T dimmed (brightness)

    Hi all,
    I work now with 4DCAPE-70T build before May 2014 and Beaglebone Black Rev. C including SD card without problems.
    Just now I tested a new 4DCAPE-70T build in 2015 and strangely the display is very dimmed!
    This is tested on the same BBB with same SD card.
    If I start the BBB without the SD card, the screen has normal brightness.
    Somebody can explain this behaviour please?
    And how to correct this?
    Thanks in advance.

  • #2
    Hello Chrigou,

    Basically, the boot order was: eMMC, uSD, UART0, USB.

    By default, during power-up, the BB uses MILO and u-boot from eMMC, so if the SD card is present, the BB will loads the uEnv.txt file from the SD card and then boots the kernel from the SD card, then it appears that the BBB boots at uSD.

    In the other instances, if the SD card is not present, the BB boot the kernel from the eMMC then it appears that the BBB boots at eMMC as also discussed here:

    Additionally, If you power up the BBB and you press for seconds the BB's BOOT button at the same time, the BB will use the MLO and u-boot on the SDCard then it seems that the BBB boots at uSD.

    Have you checked the current brightness? If not, try to check the brightness value, by utilizing the command line as shown below:

    If you're using Debian OS, from the terminal, just run:

    sudo su                                              // login as root user
    cd /sys/class/backlight/backlight                    // change the print working directory
    cat brightness                                       // this will print the brightness value
    Also, to set the brightness value to 100:

    echo  100 > brightness

    I have also found a post that is related to your concern is found here:

    Hopefully, this will help you.

    Best regards,


    • Chrigou
      Chrigou commented
      Editing a comment
      Hello kayven@4d,
      Very usefull post, thank you very much!

    • kayven@4d
      kayven@4d commented
      Editing a comment
      You're welcome! Chrigou.

      Have a nice day!