How to plot real-time with nidaq, but see the entire graph as it is plotting?

Hello,

I am using MATLAB 7.12 with Data Acquisition Toolbox 2.18. I am new to MATLAB, and am trying to simply plot an input voltage versus time in real time. I am able to plot for some duration (say ten seconds), but I have only been able to obtain one of the following results:

1) I have to wait the full ten seconds to see the graph 2) I can see one second of real-time data at a time, and then at the end of the ten seconds the entire graph becomes visible.

I would like to see the entire graph from the beginning, and watch it update as the daq collects more data.

Any suggestions?

Thanks!

Megan

[Chirag Gupta]

Could you post some sample code?

Are you using the new session based interface?

Answer 1

[Chirag Gupta]

function acquireData
s = daq.createSession('ni');
s.addAnalogInputChannel('cDAQ1Mod1',0,'voltage')
s.Rate = 2000
s.DurationInSeconds = 10;
lh = s.addlistener('DataAvailable',@plotData);
s.startBackground();
% Do something
while(~s.IsDone)
end

plot(data); %  plot global data
function plotData(src,event)
    persistent tempData;
    persistent tempTimeStamps;
    if(isempty(tempData))
         tempData = [];
         tempTimeStamps = [];
     end
     tempData = [tempData;event.Data];
     tempTimeStamps = [tempTimeStamps; event.TimeStamps];
     plot(tempTimeStamps,tempData);
end

[Chirag Gupta]

This should do the trick if you are using Compact DAQ devices with the session based architecture.

[Chirag Gupta]

if you are using the older analoginput object interface, then you should refer to this demo "Continuous Acquisition Using Analog Input" that does exactly what you need!

[W Joey]

I think it works with session-based architecture. But what if i want to get the real-time plot data?

Answer 2

[Sean de Wolski]

Use a timer function with a timerperiod of give or take 0.25s (depends on how fast your machine is)

Use the peekdata function to pull the most recent samples and plot them all inside the timer function.

obj.SampleRate; obj.Timerperiod; obj.SamplesAvailable;

will also be your friends (in the timerfunction that does the plotting). I'm on a Macintosh without the DAQ toolbox and I haven't used it in about three years; sorry I can't be more specific.

[Chirag Gupta]

peekdata

[Sean de Wolski]

Ahh of course. Your answer is far better anyway! I'm just dusting the cobwebs off my summer job for 2008.

Answer 3

[Megan]

Thanks guys! Hugely helpful :)

Answer 4

[Lee Stanley]

Hi,

Is there a way to log the plotted data as well?

Thanks.

Stan

[Sean de Wolski]

Add a save command in the callback :)

[Lee Stanley]

Hi Sean,

Could you show your coding here from the example stated above? :) By the way, is it possible to acquire and plot all the channels in a plot as well at the same time?

Thanks.