Matlab & Arduino serial communication

Question

I am trying to get some basic serial communication up and running. My arduino code is shown below.

   void setup()
    {
      Serial.begin(9600);

      Serial.println('a');
      char a = 'b';
      while (a != 'a')
      {
        a = Serial.read();
      }
    }
    void loop()
    {
    }

and my matlab code:

delete(instrfindall);
s = serial('/dev/tty.usbmodem1421');
set(s, 'BaudRate', 9600);
set(s, 'DataBits', 8);
set(s, 'StopBits', 1);
set(s, 'Parity', 'none');
set(s, 'Terminator', 'LF');
fopen(s);

% VERIFY SERIAL COMMUNICATION HAS BEEN SETUP
a = 'b';
while (a~='a')
        a = fread(s,1,'uchar');
end
if (a == 'a')
    disp('Serial read')
end
fprintf(s,'%c','a');
mxbox = msgbox('Serial Communication Initialized'); uiwait(mxbox);

The matlab code executes and I get the message box telling me that it has initialised, however the variable a is not read successfully and the while loop exits prematurely, debugging I found that it actually only loops for one iteration and then continues. 'Serial read' is never displayed.

Any help would be appreciated, thanks in advance.

Note

adding disp(size(a));disp(double(a)); after the fread yielded output 1 0 and no output respectively

For debugging purposes, could you add disp(size(a));disp(double(a)); after the fread line and append the output to your question? — Daniel
– Daniel, Commented Mar 7, 2015 at 12:36

Daniel · Accepted Answer · 2015-03-07 12:44:51Z

0

It looks like your conditions are a logical negation, but it is not. Both conditions are false for a=[] (or a=['a','b']). Reading nothing could explain the behaviour you observed. Try this code instead:

a = 'b';
while (~strcmpi(a,'a'))
        a = fread(s,1,'uchar');
end
if (strcmpi(a,'a'))
    disp('Serial read')
end

answered Mar 7, 2015 at 12:44

Daniel

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2 Comments

tjp212 Over a year ago

Thanks for your reply, when I add this code it gets stuck in the while loop, so I am not reading anything. I've also added the output as your previous comment suggested to the end of the question.

Daniel Over a year ago

@TomPower: I can't give you any hint why it's not receiving anything, but just a comment on what you are doing. There is a Arduino support package (mathworks.com/hardware-support/arduino-matlab.html) for matlab and there is a java interface (arduino.cc/en/Main/Software) which could easily be used in matlab (mathworks.com/help/matlab/using-java-libraries-in-matlab.html). It might be an alternative if you fail to solve this problem.

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