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Adding touchscreen to BBB uses up only 2 GPIO pins?

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  • Adding touchscreen to BBB uses up only 2 GPIO pins?

    Hi all,

    I am considering moving a project from Raspberry Pi to BBB wireless. The main reason being the RPi only has ~26 usable GPIO and I need around 35. The BBB definitely has enough GPIO but I need to make sure that when I connect a resistive touchscreen the GPIO's aren't used up by the touchscreen. I'm reading that the 4D touchscreens communicate to the BBB with I2C so I assume that means connecting the screen only uses up 2 GPIOs. Is that correct?

  • #2

    Are you referring to our gen4-4DCAPE products?
    What are you reading to suggest it only uses 2 GPIO?
    If you go onto their product page and download the Datasheet, it shows all of the GPIO/Pins that are used by the display cape.
    But no, it doesn't just use 2 GPIO. The touch part of the module uses I2C - correct, but that is only a fraction of the signals required as there are all the LCD signals as well.

    Please let me know if that doesn't make sense, and let me know what product you are actually referring to.



    • #3
      Yes I believe gen4-4DCAPE products, 7" model, resistive preferred but could use capacitive. How many GPIO do these products use? Like I said I am potentially migrating an existing project, very concerned on how many GPIOs I still have access to after connecting the LCD touchscreen.
      Last edited by nanok66; 31 March 2021, 01:25 PM.


      • #4
        Ah I see on page 11 it looks like the schematic shows red X's on pins the 4D display does not use?

        Click image for larger version

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        • James_4DSystems
          James_4DSystems commented
          Editing a comment
          Correct - also the Red signals you can ignore as they are optional for the button board, which is an optional extra.

      • #5
        7" CTP model is here:
        7" RTP model is here:

        Their joint datasheet:
        Page 11 shows the schematic of the Adaptor, which connects to the BBB, showing what pins are used. The gen4-4DCAPE then connects to the adaptor via a 30 way FFC cable.

        I hope that is the information you are looking for. It uses a number of GPIO. The optional ones for the button board you can ignore as they are not coded for.



        • #6
          Right on, pardon my ignorance of how many pins an LCD uses. If the red X's and red labeled GPIO pins are all still usable GPIOs that's great, enough for my project. Thanks!