Cannot close connection. MATLAB connection to Due at COM9 exists in your workspace. To create a new connection, clear the existing object.

I cannot close the ports of the arduino after a GUIDE GUI program.

All the commands I have tried at the exit function are:

try
    myArduinoAddonLibrary = getappdata(0,'ARD_AD');
    clear myArduinoAddonLibrary;
    arduinoObj = getappdata(0,'ARD');
    fclose(serial(arduinoObj.Port));
    delete(serial(arduinoObj.Port))
    clear arduinoObj;
catch errorObj
    errordlg(getReport(errorObj,'extended','hyperlinks','off'),'Arduino Error');
end

What would I be doing wrong?

The error that appears when I try to create another Arduino connection in the same port is:

 MATLAB connection to Due at COM9 exists in your workspace. To create a new connection, clear the existing object

For MATLAB 2019a

[Jason]

However, I have noticed that if I click the exit task several times, the ports duplicate? What could this be?

Instrument Object Array

   Index:    Type:     Status:   Name:  
   1         serial    closed    Serial-COM9
   2         serial    closed    Serial-COM9
   3         serial    closed    Serial-COM9

At the end of the exit task, I now run

clear all

to make sure no variables are left in the GUI workspace. And the error has now changed to:

 "Unable to create a communication link with the serial port. Please check your input argument PORT..."

However, MATLAB crashes with an internal error.

Answer 1

[Jason]

We solved it using this:

try
    clear
    myArduinoAddonLibrary = getappdata(0,'ARD_AD');
    clear myArduinoAddonLibrary;
    arduinoObj = getappdata(0,'ARD');
    fclose(serial(arduinoObj.Port));
    delete(serial(arduinoObj.Port))
    clear arduinoObj;
catch errorObj
    errordlg(getReport(errorObj,'extended','hyperlinks','off'),'Arduino Error');
end

%Remove appdata from memory

rmappdata(0,'ARD')
rmappdata(0,'ARD_AD')
clear all;

We just added clear at the start made sure the workspace was totally clear at the end.

Answer 2

[saleh said bouhliga]

In the MatLab Help Center they had nice description of how to clear a variable from memory. Check it here: https://www.mathworks.com/help/matlab/ref/clearvars.html

In your case should be: clearvars -global a;