Matlab app designer error related to an array

I'm developing a GUI to show DC-motor current and speed signals, now I'm experiencing some code difficulties.

When running the code there's an error msg related to a point used in an array which actually runs perfectly in matlab .m code.

Does anyone know how to get rid of this error?

properties (Access = private)

current % Current in mA

speed % Speed in rad/s

time % Time in s

current_temp = [];

speed_temp = [];

time_temp = [];

Data

end

Answer 1

[Adam Danz]

The table appears to be empty (running from m-file)

MQTTSignal = mqttclient('tcp://broker.hivemq.com','Port',1883)

MQTTSignal = 
  Client with properties:

        BrokerAddress: "tcp://broker.hivemq.com"
                 Port: 1883
             ClientID: ""
              Timeout: 5
    KeepAliveDuration: 60
        Subscriptions: [0×3 table]
            Connected: 1

dataTT = read(MQTTSignal)

dataTT =

  0×0 empty timetable

dataTT.Data

Error using .
Unrecognized table variable name 'Data'.

[Luis Ricardo Rivera Goitia]

Yes you were right, now I run the DC motor connected to the MQTT broker, and at the beginning it starts plotting data, but later on it stops and send me the same error.

It seems what is inside the while doesn't reconigze the .Data variable.

[Adam Danz]

I don't have experience with the Industrial Communication Toolbox so I'm not sure what the issue is. If the value of MQTTSignal or read(MQTTSignal) changes over time, you can include this snippet below to skip loops where dataTT is empty. However, if dataTT is continually empty, this will enter an infinite loop in which case it would be wise to build in an exit.

while ____

dataTT = read(MQTTSignal);

if isempty(dataTT)

continue

end

str = dataTT.Data;

end

[Luis Ricardo Rivera Goitia]

OK let me try it, thx!

[Luis Ricardo Rivera Goitia]

Here are the results

GUI Plotting View

In the video you will see that there's a gap between data probably due to the "pause(3)" command.

Any other suggestion to improve the plotting view?

Changes made to the code based on your suggestions

function StartButtonPushed(app, event)

set(app.StartButton,'Enable','off')

%app.StopButton.Text='Stop'

% Connection to MQTT

MQTTSignal = mqttclient('tcp://broker.hivemq.com','Port',1883);

Topic = "ESP32/data";

Data = subscribe(MQTTSignal,Topic);

pause(3);

%while strcmpi(app.StartButton.Enable,'off')

while strcmpi(app.StartButton.Enable,'off')

dataTT = read(MQTTSignal);

str = (dataTT.Data);

str = strrep(str, '{', ''); % remove opening bracket

str = strrep(str, '}', ''); % remove closing bracket

str = split(str,",");

app.current_temp = str2double(str(:,1));

app.speed_temp = str2double(str(:,2));

app.time_temp = str2double(str(:,3));

app.current = [app.current;app.current_temp];

app.speed = [app.speed;app.speed_temp];

app.time = [app.time;app.time_temp];

plot(app.UIAxes,app.time,app.current);

plot(app.UIAxes2,app.time,app.speed);

if strcmpi(app.StartButton.Enable,'off')

MQTTSignal = mqttclient('tcp://broker.hivemq.com','Port',1883);

Topic = "ESP32/data";

Data = subscribe(MQTTSignal,Topic);

pause(3)

end

end

[Adam Danz]

Thanks for sharing the video!

> Any other suggestion to improve the plotting view?

Yes, the plotting can be more efficient. Instead of creating a new line object every iteration, you can update an existing line object.

% Create line objects
hCurrent = plot(app.UIAxes,nan,nan); 
hSpeed = plot(app.UIAxes,nan,nan); 

% update line objects within the loop
while strcmpi(...)
        ...
        app.current = [app.current;app.current_temp];
        app.speed = [app.speed;app.speed_temp];
        app.time = [app.time;app.time_temp];
        set(hCurrent,'XData',app.time,'YData',app.current)
        set(hSpeed,'XData',app.time,'YData',app.speed)
end

[Luis Ricardo Rivera Goitia]

I already test it, and it worked though I still need to run it with this "if sentence" to make current & speed graphs run continuosly.

function StartButtonPushed(app, event)

set(app.StartButton,'Enable','off')

%app.StopButton.Text='Stop'

% Connection to MQTT

MQTTSignal = mqttclient('tcp://broker.hivemq.com','Port',1883);

Topic = "ESP32/data";

Data = subscribe(MQTTSignal,Topic);

pause(3);

%while strcmpi(app.StartButton.Enable,'off')

% Create line objects

hCurrent = plot(app.UIAxes,nan,nan);

hSpeed = plot(app.UIAxes2,nan,nan);

while strcmpi(app.StartButton.Enable,'off')

dataTT = read(MQTTSignal);

str = (dataTT.Data);

str = strrep(str, '{', ''); % remove opening bracket

str = strrep(str, '}', ''); % remove closing bracket

str = split(str,",");

app.current_temp = str2double(str(:,1));

app.speed_temp = str2double(str(:,2));

app.time_temp = str2double(str(:,3));

app.current = [app.current;app.current_temp];

app.speed = [app.speed;app.speed_temp];

app.time = [app.time;app.time_temp];

set(hCurrent,'XData',app.time,'YData',app.current)

set(hSpeed,'XData',app.time,'YData',app.speed)

% plot(app.UIAxes,app.time,app.current);

% plot(app.UIAxes2,app.time,app.speed);

if strcmpi(app.StartButton.Enable,'off')

MQTTSignal = mqttclient('tcp://broker.hivemq.com','Port',1883);

Topic = "ESP32/data";

Data = subscribe(MQTTSignal,Topic);

pause(3)

end

end