Activity Forums Questions & Troubleshooting I2C communication problem

  • I2C communication problem

  • Louis_Kortel

    July 12, 2021 at 1:34 pm

    Hello, I use a Controllino Maxi Automation board, with a 20×4 screen for displaying data. At first everything worked perfectly. Then I thought that my screen had cracked because impossible to use it even with an Arduino Uno card. So I ordered another I2C screen that I manage to use with an Arduino Uno board but not with my Controllino board. I have other I2C components like a RTC module and even a simple I2C scan doesn’t work.

    The only diagnosis I can make is that the SDA (20) and SCL (21) pins of the Controllino board are connected to the ground, even when I try to use them…

    Thank you for your help

  • Johi

    July 13, 2021 at 8:02 pm

    Hello Luis_Kortel,

    I have a Maxi-Power, i can measure the voltages on the SDA and SCL as a reference, would you like me to do this?

    How did you power the backlight to the LCD, did you provide the power via the Controlino io of via a separate source?

    Best Regards,


  • Louis_Kortel

    July 14, 2021 at 6:58 am

    Hello Johi, thank you very much for your help.

    Yes, I am happy to do so, thank you. Maybe that could help me!

    I also have at my disposal a Uno board on which I can communicate in I2C with the screen or other I2C components. But with the Controllino Maxi Automation it is impossible for me to do this.

    For power, I power the Controllino in 24V and it powers my screen via the 5V output pins.

    To communicate I use SDA and SCL (20 and 21)

    I was wondering if it was possible to flash my Controllino card with my Arduino Uno, I saw that this was possible for the Controllino Mini? Maybe that could tell me if my problem comes from hardware or software?

    Best Regards,


  • Johi

    July 15, 2021 at 7:47 pm

    Hello Louis_kortel,

    In order to help you, i did the following:

    I modified the I2C scanner and I downloaded it to my maxi-power.

    Then i measured the voltage with my Fluke 117.

    I saw varying voltages (around 3V) comming out of the pins SDA and SCL.

    I would suggest you try the same and see if there is life on these pins.

    If not i think your device might be broken.

    #include <Wire.h>

    void setup()


    Serial.begin (9600);

    } // end of setup

    void loop()


    Serial.println ();

    Serial.println (“I2C scanner. Scanning …”);

    byte count = 0;


    for (byte i = 8; i < 120; i++)


    Wire.beginTransmission (i);

    if (Wire.endTransmission () == 0)


    Serial.print (“Found address: “);

    Serial.print (i, DEC);

    Serial.print (” (0x”);

    Serial.print (i, HEX);

    Serial.println (“)”);


    delay (100); // maybe unneeded?

    } // end of good response

    } // end of for loop

    Serial.println (“Done, restarting.”);

    Serial.print (“Found “);

    Serial.print (count, DEC);

    Serial.println (” device(s).”);


    Good Luck,


  • Lukas

    July 21, 2021 at 12:33 pm

    Hello Louis,

    just an idea – it happened to me some time ago that I have received another piece of I2C display (same type, same vendor) but the I2C address was different!

    Lets use the I2C scanner to check it.



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    July 26, 2021 at 4:32 am

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