GUI button to initiate serialport object - Impossible?

Hi All

I am implementing a programmatic GUI. I want a button which, when pressed, will initiate a serialport object and connect to it and automatically stream data back to the base workspace.

Problem is, I dont think this can be done.

BGcolour = [0.20 0.92 0.86];
serial_port = "COM11";
serial_baud = 230400;
serial_connected = 0;

figureGUI = figure('position',[200 200 800 600],...
    'name','Serial Interface',...
    'numbertitle','off',...
    'resize','OFF',...
    'toolbar','none',...
    'menubar','none',...
    'color', BGcolour);
serialConnectui=uicontrol(figureGUI, 'style','pushbutton',...
    'units','pixels',...
    'position',[70 410 62 62],...
    'callback', {@serialConnect, serial_port,serial_baud});


function [] = serialConnect(src, event,serial_port,serial_baud)
        serial_connected = evalin('base', 'serial_connected');
%        s = evalin('base', 's');
        
        if (serial_connected == 1)
            disp("already connected");
        else
            fprintf("Attempting to Connect to %s at %3.0f kb/s\n", serial_port, serial_baud);
            try
                s = serialport(serial_port, serial_baud);
            catch
                disp("***Connection Failed***");
                serial_connected = 0;
                assignin('base','serial_connected',serial_connected);
                return;
            end
            configureCallback(s,"byte",1,@bytesavailable);
 %           assignin('base','s',s);
            serial_connected = 1;
            assignin('base','serial_connected',serial_connected);
            disp("***Connected!***");
            %pause(10);
        end
end

    function bytesavailable(src, ~)
        msg = read(src,src.NumBytesAvailable,"char");
        disp(msg);
    end

Here is my attempt. I cant get the data to keep streaming using my Display() function. it is because as soon as serialConnect ends, the serialport object, s, is lost. This can be demonstrated by putting a Pause(10) in directly under the line Display("***Connected***");. It will stream for 10 seconds then stop when the function finishes.

However, callbacks in GUI's cant return values, so I can't simply return s.

As you can see I have tried using evalin and its friend assignin to get a serialport from the base workspace. The problem with this is that, contrary to what https://uk.mathworks.com/help/instrument/serialport.html would have you initially believe, there is no empty constructor for the serialport object. Thus, I cannot simply declare a placeholder "blank" serialport object called s at the base workspace level.

I dont want to have my serialport connect immediately as the program starts.

Is there any workaround to tihs?

Cheers

Answer 1

[Will Haward]

I have figured it out - Not Impossible!

I added the parameter

'Parent',figureGUI,...

to my serialConnectui element

Then inside the callback function for serialConnectui, I used the following to hold onto the serialport object

set(src.Parent, 'UserData' , s)

and inversely, used the following to close the serialport when I was finished. Both callback functions come from different UI elements, but since they share a common Parent called figureGUI, I was able to open and close the serialport from two different callbacks.

set(src.Parent, 'UserData' , [])