I keep getting this error...

I am new to Matlab, and I am trying to create a blinking LED program using an arduino. After I have finished setting up my arduino and my program. I kept encountering the same error and I don't know how to fix it. The error saids, "MATLAB connection to Uno at COM3 exists in your workspace. To create a new connection, clear the existing object".

The following is my program:

a=arduino;
for i=1:10
    writeDigitalPin(a,'D13',1);
    pause(0.5);
    writeDigitalPin(a,'D13',0);
    pause(0.5);
end
disp('Done');

Answer 1

[Chris]

In your workspace, does a already exist, or some other arduino object?

if so, type clear a (or the other relevant object) in the command window. You could put that at the end of your program to try and avoid these errors in the future.

Or, as many do, simply put clear; close all at the beginning of your programs to clean the slate at the start.

[Abrahim]

Thanks a lot, the clear; workout. Apparently i did have a in my workspace.

[Chris]

You're welcome.

Answer 2

[哲史 伊藤]

I also have the same problem in R2021b and in my case the program still reporting the error even I delete using

clear
delete(instrfindall)
fclose( serial(a.Port) );
delete( serial(a.Port) );
clear a
clearvars -global DIN a

my code is following. It works fine for the first time but secondly the error occurs.

error: arduino_cycle_DIN (line 9)

MATLAB connection to Uno at COM3 exists in your workspace. To create a new connection, clear the existing object.

function arduino_cycle_DIN

delete(instrfindall)
clear
global DIN

DIN=nan(100,1);

a=arduino("COM3","Uno");

t=timer;
t.Period=0.01;
t.TimerFcn={@readDIN,a};
t.TasksToExecute=100;
t.ExecutionMode="fixedRate";
start(t)

while t.TasksExecuted<100
DIN(100)
end
delete(t)
fclose( serial(a.Port) );
delete( serial(a.Port) );
clear a
clearvars -global DIN a

function readDIN(obj,event,a)
global DIN
dat=readDigitalPin(a,"D2");
% 1
DIN(2:100)=DIN(1:99);
DIN(100)=dat;

[Chris]

@哲史 伊藤 This works fine as a standalone function for me. However, if I create a connection with the arduino in the base workspace, and then call the function, I get the error.

Normally, a variable created inside a particular workspace or function is scoped to that workspace--not accessible from another function unless passed into the function as an argument. However, since only one connection to the arduino is allowed, it would appear these connections--when made from the base workspace--are sort of global in scope.

If you type clear in the command window before calling the function, does that fix your problem?

[哲史 伊藤]

Thanks Chris,

I always type

clear

before calling the function, but still get the error.

Tetsufumi

[Chris]

@哲史 伊藤

Hi Tetsufumi,

I am stumped--but I don't use the arduino very much.

You may want to create a new question so more people will see it. If that doesn't work, you can submit a support request with Mathworks.

Best of luck.

Chris