Warning in reading data from serial port.

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Sabarinathan Vadivelu 2013-8-17

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https://ww2.mathworks.cn/matlabcentral/answers/84966-warning-in-reading-data-from-serial-port

I'm trying to read a single character 'A' from serial port, But it is issuing a warning always.

CharVar = fscanf(SerialObj,'%c',1);
Warning: Unsuccessful read: A timeout occurred before the Terminator was reached or SIZE values were available.

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Answer 1

Jan 2013-8-17

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https://ww2.mathworks.cn/matlabcentral/answers/84966-warning-in-reading-data-from-serial-port#answer_94495

The message seems to tell you, that Matlab did not receive a character and/or the corresponding terminator before the timeout occurred. So it might be useful to show us the command used for opening the port (especially the timeout value) and explain, if you are sure, that the character has been sent in the required period of time.

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Sabarinathan Vadivelu 2013-8-19

在 MATLAB Online 中打开

SerialObj = serial('COM1');
set(SerialObj,'BaudRate',9600)
vid = videoinput('winvideo', 1, 'YUY2_640x480');
src = getselectedsource(vid);
vid.FramesPerTrigger = 1;
vidRes = get(vid, 'VideoResolution');
nBands = get(vid, 'NumberOfBands');
hImage = image(zeros(vidRes(2),vidRes(1),nBands));
preview(vid,hImage);
vid.ReturnedColorspace = 'rgb';
axes(handles.axes1);
fopen(SerialObj);
try
    while(1)
        % preview(vid,hImage);
        % drawnow;
        CharVar = fscanf(SerialObj,'%c',1);
        if ~isempty(CharVar)
            if strcmp(CharVar(1),'A')
                while(1)
                    capturedImage = getsnapshot(vid);
                    faceDetector = vision.CascadeObjectDetector();
                    bboxes = step(faceDetector, capturedImage);
                    faceRegion = imcrop(capturedImage,bboxes);
                    faceRegion = rgb2gray(faceRegion);
                    obj = fspecial('unsharp');
                    faceRegion = imfilter(faceRegion,obj);
                    faceRegion = imresize(faceRegion,[400 400]);
                    imshow(faceRegion)
                    % fclose(SerialObj);
                      facePoints = detectSURFFeatures(faceRegion,'MetricThreshold',10);
                      [faceFeatures, facePoints] = extractFeatures(faceRegion, facePoints);
                      load FaceDatabase.mat
                      for i = 1 : count
                          boxPairs = matchFeatures(faceFeatures, SurfFeatures(i).features);
                          dataPoints = facePoints(boxPairs(:, 1), :);
                          queryPoints = SurfFeatures(i).points(boxPairs(:, 2), :);
                          PointsArray(i).data = dataPoints;
                          PointsArray(i).query = queryPoints;
                          countArray(i) = queryPoints.Count;
                      end
                      [maxValue,maxIdx] = max(countArray);
                      if maxValue > 30
                          % figure;
                          % showMatchedFeatures(SurfFeatures(maxIdx).face, faceRegion, PointsArray(maxIdx).data, ...
                          %     PointsArray(maxIdx).query, 'montage');
                          % title('Putatively Matched Points');
                          helpdlg(['Authorized, Face ID : ' num2str(maxIdx)],'Welcome');
                          fwrite(SerialObj,'A');
                          pause(10);
                          % [CharVar,CountVar,msg] = fscanf(SerialObj,'%c');
                          % if strcmp('S',CharVar(1))
                          %     fwrite(SerialObj,'B');
                          %     break;
                          % end
                      else
                          errordlg('Un-Authorized','Sorry');
                          fwrite(SerialObj,'B');
                          break;
                      end
                  end
                  continue;
              end
          else
              preview(vid,hImage);
              drawnow;
          end
      end
      fclose(SerialObj);
  catch
      fclose(SerialObj);
  end