Sending serial data from Arduino to Matlab error

I need to use arduino as a diy "slider" to send serial data to matlab over the span of a few minutes. There is the chance of receiving an error message during that time, not allowing me to further use the arduino.

Error code as follows:

Warning: Escaped character '\h' is not valid. See 'doc sprintf' for supported special characters.

> In matlabshared.asyncio.internal/MessageHandler/onError (line 31)

In readManVAS (line 29)

In Exp_final (line 309)

Error using matlabshared.asyncio.internal.MessageHandler/onError (line 31)

Das Gerät erkennt den Befehl nicht [system:22 at \mathworks

Error in readManVAS (line 29)

pause(0.02);

^^^^^^^^^^^

Error in Exp_final (line 309)

rating = str2num(readManVAS(s1))/10.23;

^^^^^^^^^^^^^^

(The Exp_final script at line 309 is simply using readManVAS)

Matlab code:

function VAS=readManVAS(s)
    
    % read serial input line by line until input starts with a space AND
    % can be converted into a scalar number. If 20 readlines fail, return a
    % nan value. finally flush the serial buffer once to clean up.

    firstChar="1";
    maxRead=20;
    nRead = 0;

    while firstChar~=" "
    
        nRead = nRead+1;
        if nRead>maxRead
            VAS=NaN;
            flush(s);
            return;
        end
        
        try
            tmp=char(readline(s));
            firstChar=tmp(1);
            if isnan(str2double(tmp))
                firstChar='1';
            end
        catch
            firstChar="1";
        end
        pause(0.02);
    end
    
    flush(s);
    VAS=tmp;
    %VAS=num2str(str2double(tmp));

end

Arduino Code:

// Arduino sketch for B10K Potentiometer
# include "RunningMedian.h"

const int POTPIN = A0;
RunningMedian samples = RunningMedian(23);
int potValue;
char outStr[5];

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  //for (int i=0;i<sizeof(potValues);i++){
  //  potValues[i] = 0;
  //} 
}

void loop() {
  // put your main code here, to run repeatedly:

  potValue = analogRead(POTPIN);
  samples.add(potValue);
  potValue=samples.getMedian();
  
  sprintf(outStr," %d",potValue);
  Serial.println(outStr);
  delay(10);
}

I'm thinking that non-numerical strings may be the issue, but I don't see them as is on the serial monitor.

If important, I am using Psychtoolbox 3.0.19.

I'm grateful for any kind of suggestions and steps to troubleshoot this.

Thanks

[Walter Roberson]

I notice in the isnan() case that you do

firstChar='1';

however in the other cases you do

firstChar="1";

Is there a reason for the inconsistency ?

[Vivien]

No there isn't, thank you for pointing that out!

[Walter Roberson]

Warning: Escaped character '\h' is not valid. See 'doc sprintf' for supported special characters.

> In matlabshared.asyncio.internal/MessageHandler/onError (line 31)

In readManVAS (line 29)

If I count correctly, line 29 of readManVAS is the pause() statement. It does not make any sense for the pause() statement to be generating that error message....

Unless there is asynchronous I/O happening in the background, such as accumulating data from the serial port into a buffer, and somehow the asynchronous I/O is generating that error. It does make sense for asynchronous I/O to be happening. It does not make sense for asynchronous I/O to be generating that particular error message. Any asynchronous I/O should just be buffering the incoming data, or at most doing end-of-line detection on the incoming data, neither of which would involve sprintf() ... unless there is an especially poor implementation.

I also note that the arduino code you show cannot emit a \h sequence, so I really don't understand what is happening.

[Vivien]

Hello everyone.

After trying various lines of code, I have seemingly found a solution.

The main parts in short (from what I understand), I refrained from using an indicator at the start of the string (" %d") - This way I think, the code would not completely stop, even though Matlab received junk data.

I also changed the delay up to 30, which helped a lot to reduce junk. Via smoothing, the rare junk data would not affect the results.

I'm not sure why omitting the non-number indicator helped in my case, since theoretically it should have worked either way, as far as I can tell.

Thank you all for taking a look at this!

Answer 1

[Aishwarya]

Hi @Vivien,

After reviewing the "readManVAS" function, I believe it can be optimzed better. Consider the following changes in the function:

1. There is no requirement for extra "firstChar" variable checking. You can check if the first char is whitespace using "startsWith(tmp, ' ')" function.
2. Put while loop condition so that it calls "readline" function 20 times and when space is encountered return the "VAS" value.
3. Given that you are expecting the VAS value to be numeric value, you can use "isstrprop" function to check if the characters are of "digits" category.
4. Before the "tmp" value is saved to "VAS" variable, you can remove the trailing and leading whitespaces using "strtrim" function.

Here is the modified "readManVAS" function:

function VAS=readManVAS(s)
    maxRead = 20;
    nRead = 0;
    % Assign VAS as NAN value default
    VAS = NaN;
    
    % Call readline 20 times
    while nRead < maxRead
        nRead = nRead + 1;
        try
            tmp = char(readline(s));
            % Check if tmp starts with ' ' and is not empty and is all
            % numeric avlue
            if startsWith(tmp, ' ') && ~isempty(tmp) && all(isstrprop(strtrim(tmp), 'digit'))
                % Save tmp after removing trailing spaces
                VAS = strtrim(tmp);
                flush(s);
                return;
            end
        catch ME
            % To log when error is captured
            warning("Serial read error: %s", ME.message);
        end
        pause(0.02);
    end

    flush(s);
end

Feel free to change this function according to your requirement.

In Arduino code, "Serial.println(outStr)" might not cause issue but sometimes buffer overflow or noisy characters can sneak in. Consider limiting the "outStr" value to certain digits as shown below:

// Limit to 5 digits + leading space
  sprintf(outStr, " %05d", potValue);  
  Serial.println(outStr);
  delay(10);

Kindly refer to the following documentation regarding functions used in the code:

• "sartsWith" function: https://www.mathworks.com/help/matlab/ref/string.startswith.html
• "isstrprop" function: https://www.mathworks.com/help/matlab/ref/isstrprop.html
• "strtrim" function: https://www.mathworks.com/help/matlab/ref/strtrim.html

I hope these changes help resolve the error.

[Vivien]

Thank you for your extensive answer. Nevertheless, this solution did not work for me and the error still persists (still sporadically).

I'm wondering whether this really is a problem of the code itself or rather of the energy settings (although I already tried to optimise them, I also tried using ferrit beads, simply clicking on the keyboard in case something starts "to sleep"...). Maybe there is something else I can't think of?