Not able to read into Matlab from serial (Arduino) using a timer.

I have a stopwatch code running in Arduino. I want to make a GUI in Matlab that shows the time and also has buttons to control the stopwatch.

I am using a timer in Arduino to increment the second of the stopwatch. When this happens, I want to send a serial command to Matlab so I can update the GUI.

I made a timer function that gets called 4 times a second. Its getting called, but I cannot read anything from serial inside. This is my first experience with serial communication and I'm a complete beginner with Matlab so I hope someone can help me out.

I have the following code inside the OpeningFcn function:

global s;
s = serial('COM11','BaudRate', 115200);
set(s,'Terminator','LF');
set(s,'Timeout',0.2);
fopen(s);
%s.ReadAsyncMode = 'manual';
pause(3);
disp('Connected.');
handles.timer = timer('Period',0.25,                  ... 
                      'StartDelay',1,                 ... 
                      'TasksToExecute',inf,           ... 
                      'ExecutionMode','fixedSpacing', ...
                      'TimerFcn',{@timerCallback}); 
start(handles.timer);

And I have this for the timer function:

function timerCallback(~,~)

      try

          readasync(s);
          n = s.BytesAvailable;
          if n > 0
              in = fscanf(s);
              disp(in);
          end

      catch 
      end
  end

In Arduino I'm using Serial.println(second);

Before I was using a while loop instead of a timer (in Matlab) and I could read the data. But the GUI never showed up since the code was stuck inside the loop.

Answer 1

[Geoff Hayes]

Ahmed - how does the timerCallback know about s since it isn't declared there as a global or otherwise? Rather than making is a global variable, you could add s to your handles structure and then access that from your callback. In the OpeningFcn you would change the code to

 % same as before
 handles.s     = s;

 handles.timer = timer('Period',0.25,                  ... 
                      'StartDelay',1,                 ... 
                      'TasksToExecute',inf,           ... 
                      'ExecutionMode','fixedSpacing', ...
                      'TimerFcn',{@timerCallback,hObject});

 guidata(hObject,handles);

 start(handles.timer);

Note how we pass hObject as an input parameter to timerCallback. Here we assume that hObject is the handle to your figure/GUI.

Now in the timer callback we do

 function timerCallback(~,~,hObject)

 handles = guidata(hObject);

 if isfield(handles,'s')
     try
          readasync(handles.s);
          n = handles.s.BytesAvailable;
          if n > 0
              in = fscanf(handles.s);
              disp(in);
          end
      catch 
      end
 end

Try the above - perhaps it will allow you to proceed.