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  • Fake digital Input signal

     tobiascapin updated 3 years, 5 months ago 3 Members · 6 Posts
  • tobiascapin

    January 22, 2021 at 6:59 pm

    Dear sirs,
    I’m using a Controllino Mega for a automation project. I have to control some doors and semaphores. All signals are 12VDC and the Controllino is powered with 12VDC.

    I have some trouble because some inputs somehow get a dirty logic state when the input circuit is open.
    For example I have an emergency button normally closed, when I push it, the circuit opens leaving the input wire without any signal.

    The Controllino detects an input and the logic state stays on with an open wire. Its led is not fully on, but brights softly. When I close the circuit releasing the button, the bright is full, when I push it (opening the circuit) the bright the softer.

    I tought it can be a noise in the open wire, the wire is about 20-30m long and passes near other signals, 220V, solenoids for door locks etc.
    Then I was woundering if the Controllino digital input needs a pull-down resistence or something like this like an Arduino, I did not find anything about these specification in the Controllino datasheet and honestly I would expect an automatic handling about input from a PLC, but maybe I’m wrong and I need a pull-down configuration too.

    Do you have any idea about this problem?

    Thanks for your help.

  • Franju

    January 24, 2021 at 11:06 pm


    What about to try doing contact to the input with a cable connected to 12v, and after connected to 0V, and check if the eratic state of the input is gone ? If so, it would mean, I think, that you need a pullup or pulldown resistor, depending to your project.
    Or maybe a switch connected for exemple NC to 12v and NO to 0V ?

    • This reply was modified 3 years, 5 months ago by  Franju. Reason: orthographe
  • tobiascapin

    January 28, 2021 at 6:09 pm

    Unfortunately I cannot have a SPDT switch to ground the signal when not pressed. Anyway finally I think I have solved using an extra external pulldown resistance of 10K.

    I tryied to get direct support from Controllino, I had a first reply but I did not have any information related to internal resistence. The documentation has not information about this requirement and moreover has no information about the internal pulldown resistance value.

    I’m really disappointed with the lack of documentation and of the support.

    • Franju

      January 29, 2021 at 6:21 pm

      I think you can have a look on the Atmega 2650 microcontroller datasheet, as it is the one used in controllino Mega.
      Still my opinion : the internal pullup resistance would be those of the Atmega. So its datasheet would tell you. And so there is no internal pulldown resistors.

    • Lukas

      February 16, 2021 at 12:56 pm


      each digital/analog input already has internal pull-down resistor as a part of the voltage divisor inside. The behaviour you describe seems to be caused by really high noise on the line. Nevertheless I will try to investigate it more.



      • tobiascapin

        February 17, 2021 at 2:33 pm

        Dear Lukas, I did not find the value of these internal pull-down resistors in the documentation.
        By the way seems I have solved with an additional external 10k pulldown resistance, I agree the problem was an high noise due to the long wire.

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