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Eamon
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How do I plot live data acquired via a NIDAQ inside a GUI window?

Asked by Eamon
on 5 Jul 2016
Latest activity Commented on by Eamon
on 19 Jul 2016
I currently have a function which plots data acquired via a NIDAQ (NI USB-6218) in real time. This is the following function, "acquirelive" :
% acquirelive function:
% acquire signal in real time
global time;
global data;
s = daq.createSession('ni');
addAnalogInputChannel(s,'Dev1', 0, 'Voltage');
s.Rate = 1000;
s.DurationInSeconds = 10;
lh = addlistener(s,'DataAvailable', @collectData);
s.startBackground();
This function calls the collectData function, which is the following:
function collectData(s,event)
time = event.TimeStamps;
data = event.Data;
h = animatedline(time,data);
end
This works well and plots the data in real-time over a 10 second period. However, when I attach this "acquirelive" function to a button in a GUI I'm designing using GUIDE, the GUI opens but nothing happens when the plot button is clicked (inside or outside the GUI). There is also no error message generated. This is the code associated with the button in the GUI:
function PlotButton_Callback(hObject, eventdata, handles)
acquirelive;
The GUI is pretty simple. There are no buttons aside from the plot button (it looks like this):
Any ideas why the placement of the function inside the GUI causes this problem? Do I need to initialize the axes of the plot in the code at some point?
Thanks for any advice you might have, I appreciate it! Let me know if more information is needed to answer the question.

  2 Comments

Eamon - you may want to put a breakpoint at the line where you call acquirelive from the pushbutton callback so that when you press the button, you can start stepping through the code within the acquirelive script. When you do so, check to see if all variables are initialized properly.
If all code seems to be getting initialized proper but still nothing happens, then try copying and pasting the code from this script into your pushbutton callback (less the global variables since they seem to be unused). Or better yet, save the s to the handles structure so that you don't "lose" it and can access it again (to perhaps stop the data acquisition). Something like
function PlotButton_Callback(hObject, eventdata, handles)
handles.s = daq.createSession('ni');
addAnalogInputChannel(handles.s,'Dev1', 0, 'Voltage');
handles.s.Rate = 1000;
handles.s.DurationInSeconds = 10;
lh = addlistener(handles.s,'DataAvailable', @collectData);
handles.s.startBackground();
guidata(hObject, handles); % to save the updated handles structure
Does the above make a difference?
Hi Geoff, thanks for your response! Your suggested change works. It generates a new window displaying the real-time signal. However, it doesn't display inside the GUI window itself, which is what I'm aiming for. I'll look into that, but any further suggestions you have would be appreciated. Thanks again.

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2 Answers

Answer by Vinod
on 13 Jul 2016
 Accepted Answer

  1 Comment

This works well. Thanks Vinod!

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Answer by Geoff Hayes
on 6 Jul 2016
Edited by Walter Roberson
on 9 Jul 2016

Eamon - animatedline allows you to specify which axes you wish to create the line in, so you will need to pass the handle to your axes into the collectData callback. If the Tag property for your axes is axes1, then I think that you can do something like
...
lh = addlistener(handles.s,'DataAvailable', {@collectData,handles.axes1});
...
In the above, we just pass the axes handles as an input to the collectData function. This function will then change to
function collectData(s,event,hAxes)
time = event.TimeStamps;
data = event.Data;
h = animatedline(hAxes,time,data);
end
That should work. One thing you may want to consider is the line
h = animatedline(hAxes,time,data);
With it, you will be creating a new graphics object each time. This may be a problem depending upon often you are creating a line (does the rate refer to how many times a second or..?). An alternative is to create one animated line and just update its data over time. See the examples from the documentation and how the function addpoints is used.

  15 Comments

Geoff - I think I figured out why it wasn't working, but I'm still working on solving the main problem. The error I explained above happens if I have more than one figure open. As in, if I open the non-GUIDE version of the optotracker figure in addition to running the optotracker code which opens the figure. I think this might be because there are multiple figures open with the same handles then MATLAB isn't sure which figure the program refers to.
So, now if I run optotracker and close all other figures, I get a new error, which I've copied below.
Warning: Error occurred while executing callback:
Error using animatedline
Invalid type for argument X. Type should be double.
Error in collectData (line 8)
h=animatedline(handles.axes1,time,data);
This error doesn't make sense to me because according to this page you should be able to specify the axes before you specify the x and y data to be plotted using the animatedline function, using the following syntax:
h = animatedline(ax,___) creates the line in the axes specified by ax instead of in the current axes (gca). The option ax can precede any of the input argument combinations in the previous syntaxes.
Maybe this means I am not referencing my axes handles correctly. I'll look into it. Thanks for any ideas you may have. You've been working with me on this for quite some time! Again, for reference, this is my collectData function:
function collectData(s,event,hAxes)
time = event.TimeStamps;
data = event.Data;
hGui = findobj('Tag','optogui');
if ~isempty(hGui)
handles = guidata(hGui);
if isfield(handles,'axes1')
h=animatedline(handles.axes1,time,data);
end
end
end
And this is the PlotButton call in my optotracker GUI:
function PlotButton_Callback(hObject, eventdata, handles)
% hObject handle to PlotButton (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
handles.s = daq.createSession('ni');
addAnalogInputChannel(handles.s,'Dev1', 0, 'Voltage');
handles.s.Rate = 1000;
handles.s.DurationInSeconds = 5;
lh=addlistener(handles.s,'DataAvailable', @collectData);
handles.s.startBackground();
guidata(hObject, handles);
Eamon - I would put a breakpoint at the line
h=animatedline(handles.axes1,time,data);
and then run your GUI. When the debugger pauses at this line, check to see what is handles.axes1, time and data. It could be that the error message is referring to the time array. Check the type of each using
class(time)
class(data)
Perhaps the time array (which is the x input to animatedline and must be of type double) is an (say) integer array instead.
Hi again, Geoff. I apologize for the delayed response. It seems that both the time and data arrays are of type double. The only part of the argument which is not, is the handles.axes1, which is of type matlab.graphics.axis.Axes, which would mean that the handles.axes1 is the part of the argument triggering the error. This seems odd given that the animatedline function is supposed to allow axes as the first part of the argument. I will look into alternative ways of using animatedline. Thanks again!

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