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Ploting analog input in real time

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Raldi on 7 Dec 2011
Hey evereyone I have the following code
input=analoginput('winsound'); set (input, 'SampleRate', 8000); set (input, 'SamplesPerTrigger', 1000); num=1000; set (input, 'TriggerRepeat', inf); start(input)
while "something" data = getdata(input); flushdata(input); plot("data"); plot("fft data spectrum") stop(input) delete(input); end
The data plot shows fine, but the second plot will only show something for 1 second just after i run the code and then it shows nothing. Why is that happening?

Answers (2)

Gautam Vallabha
Gautam Vallabha on 8 Dec 2011
It is possible that one of your plots is being overwritten by the other plot. The standard plot command (plot(x,y)) uses the current figure and axes (gcf and gca), the default behavior is that a new plot will replace any existing plots.
You might try explicitly using different axes, e.g.
ax1 = subplot(2,1,1);
ax2 = subplot(2,1,2);
while (...)
plot(ax1, time, amplitude);
plot(ax2, freq, power);
By the way, for better performance, instead of calling plot each time, consider calling it once (before the while loop), and then setting xdata and ydata, e.g.:
h = plot(ax1, time, amplitude);
set(h,'xdata', newTimeData, 'ydata', newAmplitudeData);
  1 Comment
Raldi on 8 Dec 2011
but they are on different objects axes1 and axes2, how can this happen?

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Walter Roberson
Walter Roberson on 8 Dec 2011
Do not stop() and delete() input within the loop.
Within the loop, add a drawnow() call after the plot() call.
Walter Roberson
Walter Roberson on 9 Dec 2011
Please see my comment to my answer in
Raldi on 11 Dec 2011
Either i didnt understand you answer well or it doesnt work in my case cause it still didnt show anything on the spectrum analisation axes.

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