Real time plotting from hardware

[astodolski]

I want to plot the real time output from a piece of hardware through its ADC. It is not a sine or square function but it is periodic in the sense that the start of samples to the sample size is periodic. The output has no zero crossings - it is essentially positive. I use a plot widget from the designer (all the UI widgets are laid out in the designer). Does the Qwt oscilloscope example represent the best way to implement this type data acquisition or is there a better example? I have version 6.1 rc3 version of Qwt.

Thanks for any help

[Uwe]

oscilloscope is more a demo than an example - showing what is possible with almost no CPU usage. F.e the curve always grows from left to right to be able to draw incrementally. But its code is not intended as a beginner tutorial.

One thing that is important for your type of plot: decouple data acquisition ( sample rate ) from the the refresh rate ( QwtPlot::replot ). This can be done easily, by setting up a timer that increments the scale interval ( QwtPlot::setAxisScale ) periodically. Also it is a good idea to understand QwtSeriesData<QPointF> for your concept how to pass or share your sample buffer with the corresponding curve.

Uwe

[astodolski]

oscilloscope is more a demo than an example - showing what is possible with almost no CPU usage. F.e the curve always grows from left to right to be able to draw incrementally. But its code is not intended as a beginner tutorial.
Uwe

Thanks for that reply. I was using the reference of the oscilloscope as a "basis" for taking samples in a separate thread and displaying them periodically. That seemed like a good starting point.

One thing that is important for your type of plot: decouple data acquisition ( sample rate ) from the the refresh rate ( QwtPlot::replot ). This can be done easily, by setting up a timer that increments the scale interval ( QwtPlot::setAxisScale ) periodically. Also it is a good idea to understand QwtSeriesData<QPointF> for your concept how to pass or share your sample buffer with the corresponding curve.

Would you please expand on decoupling DA from the refresh rate? They are synchronous. If I understand what your getting at, a QwtSystemClock object would manage the data sample rate and a QBasicTimer would handle the refresh rate for each timer tick.

[K4ELO]

Here: http://www.music.mcgill.ca/~gary/rtfft/
is source code in Qt/Qwt that you may find useful.

It does require some simple changes if you are using Qt 5 and latest Qwt.

[astodolski]

Here: http://www.music.mcgill.ca/~gary/rtfft/
is source code in Qt/Qwt that you may find useful.

It does require some simple changes if you are using Qt 5 and latest Qwt.

I'll give it a look, thanks.

[astodolski]

Simple changes to say the least. fftw library doesn't appear to be able to build on a Windows platform. It also assumes Qwt is not installed already - using a local Qwt.