Arduino clearing existing connection issue

I have declared a global object arduino() and in a different function I would like to clear this connection and create another. It keeps saying that the connection to arduino is existing eventhough I use "clearvars -global a".

Error: "MATLAB connection to Uno at COM3 exists in your workspace. To create a new connection, clear the existing object."

    function ClearArduino(app)
            clearvars -global a
            
            a = arduino('COM3', 'Uno');   %Error is on this line
            
            writeDigitalPin(a, 'D11', 0);
            writeDigitalPin(a, 'D12', 0);
            writeDigitalPin(a, 'D13', 0);
        end
        
	 function runArduinoCode(app, indicator)
				
            clearvars -global a
            
            a = arduino('COM3', 'Uno');
            
            while indicator == "On"
 
                writeDigitalPin(a, 'D11', 1);
                pause(0.5)
                writeDigitalPin(a, 'D11', 0);
                
                writeDigitalPin(a, 'D12', 1);
                pause(0.5)
                writeDigitalPin(a, 'D12', 0);
                
                writeDigitalPin(a, 'D13', 1);
                pause(0.5)
                writeDigitalPin(a, 'D13', 0);
                
            end
            
            clear a;
       end
	   

[Laura Letellier]

Did anyone ever find a solution for this?

My students are encountering this issue and the only way we can 100% clear the existing object is to exit MATLAB, unlpug the Arduino, replug, and restart MATLAB.

If any of the MATLAB software developers are monitoring this, please tell us how to even see the workspace when using App Designer and then give us a hint as to how to clear the connection. Since you are throwing the error you must have some way to access the associated pointer, handle, or hwind to know that the connection is unavailable. If so there must be a way for us to programmatically release it.

Thank you!

Answer 1

[Geoff Hayes]

Borian - why not define a property in your app that represents the arduino object so that all callbacks have access to it? See Share Data Within App Designer Apps for details. Presumably you would do something like

properties (Access = private)
        arduinoObject = [] % arduino object
end

and your callbacks (?) would become something like

function ClearArduino(app)

    if ~isempty(app.arduinoObject)
        clear(app.arduinoObject);
    end
    app.arduinoObject = arduino('COM3', 'Uno');
    
    writeDigitalPin(app.arduinoObject, 'D11', 0);
    writeDigitalPin(app.arduinoObject, 'D12', 0);
    writeDigitalPin(app.arduinoObject, 'D13', 0);
end

function runArduinoCode(app, indicator)

    if ~isempty(app.arduinoObject)
        clear(app.arduinoObject);
    end
    app.arduinoObject = arduino('COM3', 'Uno');
    
    while indicator == "On"
    
        writeDigitalPin(app.arduinoObject, 'D11', 1);
        pause(0.5)
        writeDigitalPin(app.arduinoObject, 'D11', 0);
        
        writeDigitalPin(app.arduinoObject, 'D12', 1);
        pause(0.5)
        writeDigitalPin(app.arduinoObject, 'D12', 0);
        
        writeDigitalPin(app.arduinoObject, 'D13', 1);
        pause(0.5)
        writeDigitalPin(app.arduinoObject, 'D13', 0);
        
    end
end

I have no idea if the above will work but it may be something to start with.

[George Aiken]

This worked for me, thanks.

Fixed the comm port error and the LEDs turn on, thanks.

[franck tinkeu]

We Can try " clear Arduino" at the Window command

[franck tinkeu]

We Can try it before beginning the next programm!!!

Answer 2

[shaherbano zaidi]

I was encountering the same issue i just added "Clear all' at the top of my code.

Answer 3

[Makenzie]

To avoid the “Error using arduino (line 156) MATLAB connection to UNO at COM3 exists in your workspace. To create a new connection clear the existing object.

Unplug and replug the arduino into the computer, instead of clicking on the arduino’s name you set up. Click set up by usb, then in the top left click hardware setup and go through all of the steps. I don’t select any special libraries. This should work. Make sure to have all of your variables cleared beforehand.

I’ve been having to do this everytime I connect my computer to the arduino even when all objects/workspace variable are cleared.