Serial data lag when transmitted without delay

Hello Community!

I want to display Serial Data from an Arduino Uno Photodiode Array(16 by 1 Elements). The values are 8 bit. The arduino also turns a stepper motor after each aquisition, so you get some sort of basic computer tomography image.

Problem is, that the data should be displayed in realtime for learning purpose, but if the data is sent by the Arduino (115200 baudrate) without a delay of 5 ms after each 8 bit value, the imagesc() /drawnow() function gets delayed be approximatly 20 sec.

If a delay of 5 ms on the arduino side is added, the drawnow() function feels nearly realtime responsive. But i can't leave that delay in, because the steppermovement would get choppy.

I guess it has to do with the ineffective way of plotting on the Matlab side. Or maybe the standard serial buffer is to small (12 steps per sec*16 values of 8bit(or 1 byte)=192 bytes per second)? Could anybody suggest better practice?

Thank you,

Markus

Code:

A=zeros(16,360); %Defines 16 diodes array with 360 degrees rotation/steps
B=size(A,2);
serialPort = 'COM3';            % defines COM port of Arduino Matlab Command "seriallist" zeigt alle vorhandenen
s = serial(serialPort,'BaudRate',115200)

fopen(s);
pause(2); % Pause of 2 sec is crucial, otherwise connection is not established correctly
 figure('Name','Sinogram')
 
 fprintf(s,'%c','a'); %starting command for the image aqusition 
 try
for y=1:B
    for x=1:16
      
       dat = fscanf(s,'%d');  %reads serial data
        A(x,y)=dat; %fills Matrix 
        
    end
    disp(floor(y/B *100)+"% loaded");
    drawnow('limitrate')
        imagesc(A)
        xlabel('Angle - \theta (degree)'); 
        ylabel('Value - x\prime (Pixel)');
end
 catch
     instrreset;
     
 end

fclose(s);
disp('Data aquiered');
colorbar;

[Joao Ferreira]

Try adding the function:

flushinput(serialPort);

after the drawnow, so Matlab discards any data buffered..