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

Asked by Megan on 15 Jul 2011

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

1 Comment

Chirag Gupta on 15 Jul 2011

Could you post some sample code?
Are you using the new session based interface?

Megan

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4 Answers

Answer by Chirag Gupta on 15 Jul 2011
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

2 Comments

Chirag Gupta on 15 Jul 2011

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

Chirag Gupta on 15 Jul 2011

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!

Chirag Gupta
Answer by Sean de Wolski on 15 Jul 2011

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.

2 Comments

Chirag Gupta on 15 Jul 2011

peekdata

Sean de Wolski on 15 Jul 2011

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

Sean de Wolski
Answer by Megan on 18 Jul 2011

Thanks guys! Hugely helpful :)

0 Comments

Megan
Answer by Lee Stanley on 23 May 2013

Hi,

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

Thanks.

Stan

2 Comments

Sean de Wolski on 23 May 2013

Add a save command in the callback :)

Lee Stanley on 23 May 2013

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.

Lee Stanley

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