Serial Communication Code Error

h=instrfindall;
for i= 1:length(h)
    fopen('COM'+string(i))
end
h=instrfindall;
str=string(h.name(find(cell2mat(h.BytesAvailable))));

fclose('all');
fopen(str);

I developed this code on friday for finding out on which Port my Arduino is plugged in and it actually worked. Today I tried to implement the code into my GUI and an error is appearing.

Error: Struct contents reference from a non-struct array object.

What do I have to do, so that the error won't appear anymore?

Thank you for your help

Answer 1

[Nate]

Hi Tobias,

Could you please provide more information?

1) Does the code still work correctly when it is not in a GUI? 2) Could you please provide the full error? I am interested in knowing which line causes the error.

Thanks, Nate

[Tobias Wzl]

No unfortunately not, but in first place it worked in both ways I don't know what's wrong now.

If run the code separate outside of a GUI the error appears in line 6:

*Struct contents reference from a non-struct array object.

Error in Untitled (line 6) str=string(h.name(find(cell2mat(h.BytesAvailable))));*

Answer 2

[Walter Roberson]

You would get that error if instrfindall returns empty.

[Tobias Wzl]

but how could it be that instrfindall returns empty if some device like my Arduino is plugged in? It's confusing me because this worked in first place when I created this code...

[Walter Roberson]

None the less, put in a test for h being empty. If it is an "impossible" situation then your error about non-struct will not disappear. If somehow it can happen then you will avoid the error.

[Tobias Wzl]

i checked if h is empty or not and it somehow it is.

but doesn't the command 'instrfindall' provide to search for all of my ports whether they are closed or open? Or did I get something wrong here?

[Walter Roberson]

It has been known to happen in the past that instrfind has lost track of a port, and that it was necessary to restart MATLAB to find it again. In the time that was happening most often there was no way to force a bus rescan. Part of the problem back then was that when this was happening most often, USB serial ports could only be detected if the device was plugged in at the time MATLAB was started. That should no longer be the case in current versions, but it used to happen. (You do not happen to mention your MATLAB version.)

[Tobias Wzl]

Sorry I was so desperate about the code that I forgot to mention the version I'm using... I'm currently using 2017a

I already tried to restart Matlab again, because this would've been the easiest way to make it work again but unfortunately it isn't^^

And my Arduino is plugged in all the time.

[Walter Roberson]

What is returned if you execute

com.mathworks.toolbox.instrument.Instrument.jinstrfindall

Also, try

instrreset

[Tobias Wzl]

if I execute the first command an empty answer appears --> ans=[]

if I execute the second command Matlab tells me that the function is undefined

And sorry for the late answer I was ill for the last whole week

[Walter Roberson]

Hmmm, instrreset has been around in Instrument Control Toolbox since before R2006a; https://www.mathworks.com/help/instrument/instrreset.html

Anyhow, I do not know why your devices cannot be seen, unless perhaps the system considers them to already be in use for something else. Perhaps this link will help: http://www.intech.co.nz/downloads/help/mscanv5/faq_84.htm