Having trouble connecting serial port inside GUI

So some background: I'm making a small app that can read pump performance from a flow and pressure sensor thats connected to a UNO board, and I'm wanting to have it read live data through the serial connection. Problem is that it doesn’t want to open the serial port connection properly inside of my application (made using the app designer). This is the error message that I get:

Error using internal.Serialport

Unable to connect to the serialport device at port 'COM3'. Verify that a device is connected to the port, the port is

not in use, and all serialport input arguments and parameter values are supported by the device.

See related documentation for troubleshooting steps.

Error in serialport (line 116)

obj = internal.Serialport(varargin{:});

I can open and read the serial port just fine outside of my GUI code, but can’t seem to get it working when its running inside the app.

Any help or ideas would be greatly appreciated.

Here is the code I have so far:

 s=serialport("COM3",9600);
            a=0;
            F=1;
            setappdata(app.Image_2,'stopvalue',a);
            
            while a==0
                Data(F,:)=readline(s);
                if numel(Data(F,:))<3
                    continue
                elseif numel(Data(F,:))>3
                    %error('Input data has too many variables')
                    app.Label_4.Text='Input data has too many variables';
                    break
                end
                V=Data(F,1);
                C=Data(F,2);
                DT=Data(F,3)/1000;
                P=((V/5)/0.0018)-22.22;
                FR=(C*0.00303)/DT;
                T=T+DT;
                H = (P)/(9.81);
                HP = (FR*P)/1000;
                drawnow limitrate
                addpoints(PvsT,T,P);
                addpoints(FRvsT,T,FR);
                addpoints(HvsFR,FR,H);
                addpoints(HPvsFR,FR,HP);
                a=getappdata(app.Image_2,'stopvalue');
                F=F+1;
                setappdata(app.DataExport,'DataMatrix',Data);
            end

Kit Leeming

[Kit Leeming]

Also before anyone gets all up me for using a while loop instead of a counter, I'm not all that great yet and don't want to go through the hassle for something that I want to try and keep simple and finish quickly

[Abdulkadir Arslan]

I am having a similar problem. Could you find any solution?

This is my question: internal.Serialport error

Answer 1

[Pratyush Swain]

Hi Kit,

I understand you are unable to connect to your serial port device from inside the application.Here are some of the steps/workarounds to troubleshoot and resolve the issue:

1. Check port availability: Ensure that the serial port "COM3" is not being used by another application, including other instances of MATLAB. Only one application can use a serial port at a time.
2. Run MATLAB as Administrator: Sometimes, permission issues can prevent MATLAB from accessing the serial port. Try running MATLAB as an administrator to see if that resolves the issue.
3. Use "instrfind" to check for open serial objects: Use "instrfind" to check for any open serial port objects that might be blocking the connection. If there are any, close and delete them before trying to connect again.
4. Implement error handling: Add error handling in your code to catch any issues when attempting to open the serial port and provide a user-friendly message..

You can make the following modifications to your implementation:

% Clear any existing serial connections
if ~isempty(instrfind)
    fclose(instrfind);
    delete(instrfind);
end

% Attempt to create the serialport object with error handling
try
    s = serialport("COM3", 9600);
catch e
    uialert(app.UIFigure, e.message, 'Serial Port Error');
    return; % Exit the function if the serial port cannot be opened
end

% Initialize variables for the loop
a = 0;
F = 1;
setappdata(app.Image_2, 'stopvalue', a);

%  Main loop implementation for reading data
%   ------


% Close the serial port when done
clear s

Please refer to a similar query on connecting serial port from app designer for more information: https://www.mathworks.com/matlabcentral/answers/1730055-connecting-arduino-to-app-designer-with-drop-down-and-button

For more information on "instrfind" function,please refer to https://www.mathworks.com/help/matlab/ref/instrfind.html

Hope this helps.