COM port error and function error in serial communication with arduino and matlab

i get this error:Error using serial/fopen (line 72)

Open failed: Port: COM3 is not available. Available ports: COM1.

Use INSTRFIND to determine if other instrument objects are connected to the requested device.

Error in bodekkealgo>automate (line 26)

fopen(ard);

clc;
clear all;

CAMERA = videoinput('pointgrey', '1');%camera initialization
start(CAMERA);


for b = 1:8
    automate(CAMERA)
    pause(8)
end

fclose(ard)
stop(CAMERA);                      %stop camera acquisition

function[addition] = bodekke(imagename)  %bodekke function mathematics behind the autofocus detection
im = double(imread(imagename))
bd = [-1 0 1]
cbd = conv2(im,bd)
squaredcbd = cbd.^2
addition = sum(squaredcbd(:))
end
       
function automate(CAMERA)
ard = serial('COM3','BaudRate',9600);  %arduino initialization
fopen(ard);
pause(1);
for i = 1:30    %to capture images
    
filename = sprintf('testtry%02d.jpg',i);
img = im2double(getsnapshot(CAMERA));  %captures images
img = rgb2gray(img);
imwrite(img,filename)

end

D = 'C:\Users\PRL\Desktop\just';  %location where image  is stored
S = dir(fullfile(D,'*.jpg'));      
for k = 1:numel(S)              %applies bodekke to all images
    F = fullfile(D,S(k).name);
    addition(k) = bodekke(F);        %bodekke function call                                                                                
end
plot(addition);                     %plotting values just for our visual understanding
[m,index] = max(addition)
hold on
plot(index,m,'*')
hold off
title("bodekke with spot images")
fprintf(ard,'%d',index)            %"here is where we send the position of image to arduino"                                  

end

Answer 1

[Charan Jadigam]

Hi,

The mentioned error occurs because of 2 reasons.

1.The port COM3 might have been already opened and the corresponding serial object might still be in the workspace. So, try deleting the serial object.

clear <serial_object>

2.The serial port ‘COM3’ is not connected to Arduino. Verify the port to which Arduino is connected in the ‘Device Manager’ and use the appropriate port.