Assistance Needed with Oscilloscope Integration Using Waveform SDK in Qt

[Fausto]

Posted for @fahiz.

I am currently developing a custom GUI with Qt, which includes an oscilloscope. I'm utilizing the ADP 3450. My task involves plotting waves with a frequency of 1 million Hz and an amplitude of 1 Vpp. Additionally, it operates in burst mode with a trigger interval of 1 second. Currently, I'm employing FDwfAnalogInAcquisitionMode as scanmodeshift.

I'm encountering below issues:

The time range is very limited (currently at 0.2 seconds), which prevents me from observing more than one wave bunch. Ideally, I would like to visualize multiple pulses over a couple of seconds.

Another issue lies in the plot amplitude, which doesn't reach 0.5 V and -0.5 V. but, increasing the frequency allows it to touch the peaks.

Could you advise on how to address these issues and suggest the correct method for plotting in such cases?
I am adding one screenshot also with this.

 

 

I am using the SDK (C++) provided by Waveform, and the Qt version is 5.15.3. I am generating and plotting with the same device (ADP 3450). I also attempted generating from another source. I am providing the header file and source file of the basic Qt code (I am using QCustomPlot for plotting).

Header (mainwindow.h):

 

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "qcustomplot.h"
#include <digilent/waveforms/dwf.h>
#include <unistd.h>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow {
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

    void setupRealtimeDataDemo(QCustomPlot *customPlot);

private slots:
    void realtimeDataSlot();

private:
    Ui::MainWindow *ui;
    QTimer dataTimer;
    HDWF hdwf;
    STS sts;
    double hzAcq = 1500000;
    const int nSamples = 2000000;
    QVector<double> rgdSamples;
    int cValid;
    char szError[512];
    double sinAmplitude;
    double sinFrequency;
    double wf_run_time;
    double wf_wait;
};

#define Wait(ts) usleep((int)(1000000*ts))

#endif // MAINWINDOW_H

 

Source code (mainwindow.cpp):

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <fstream>

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow) {
    ui->setupUi(this);
    setGeometry(400, 250, 542, 390);
    setupRealtimeDataDemo(ui->customPlot);
    connect(&dataTimer, SIGNAL(timeout()), this, SLOT(realtimeDataSlot()));
    dataTimer.start(100); // Adjust the interval based on your preference
}

void MainWindow::setupRealtimeDataDemo(QCustomPlot *customPlot) {
    rgdSamples.resize(nSamples);

    if (!FDwfDeviceOpen(-1, &hdwf)) {
        FDwfGetLastErrorMsg(szError);
        return;
    }

    FDwfDeviceAutoConfigureSet(hdwf, 0);

    // Setup sine wave generation parameters
    sinAmplitude = 1.0;
    sinFrequency = 1000000.0;
    wf_run_time = 0.2;
    wf_wait = 0.8;

    // Configure Digilent Analog Out for sine wave generation
    FDwfAnalogOutNodeEnableSet(hdwf, 0, 0, 1);
    FDwfAnalogOutNodeFunctionSet(hdwf, 0, 0, 1); // Sine function
    FDwfAnalogOutNodeFrequencySet(hdwf, 0, 0, sinFrequency);
    FDwfAnalogOutNodeAmplitudeSet(hdwf, 0, 0, sinAmplitude);
    FDwfAnalogOutRunSet(hdwf, 0, wf_run_time);
    FDwfAnalogOutWaitSet(hdwf, 0, wf_wait);
    FDwfAnalogOutRepeatSet(hdwf, 0, 0);
    FDwfAnalogOutConfigure(hdwf, 0, 1);

    // Configure Digilent Analog In for data acquisition
    FDwfAnalogInChannelEnableSet(hdwf, 0, 1);
    FDwfAnalogInChannelRangeSet(hdwf, 0, 5);
    FDwfAnalogInAcquisitionModeSet(hdwf, 1); // acqmodeScanShift
    FDwfAnalogInFrequencySet(hdwf, hzAcq);
    FDwfAnalogInBufferSizeSet(hdwf, nSamples);
    FDwfAnalogInConfigure(hdwf, 1, 0);

    Wait(2);

    FDwfAnalogInConfigure(hdwf, 0, 1);

    // Setup the QCustomPlot for visualization
    customPlot->addGraph();
    customPlot->graph(0)->setPen(QPen(QColor(40, 110, 255)));
    customPlot->axisRect()->setupFullAxesBox();
    customPlot->xAxis->setRange(0, nSamples);
    customPlot->yAxis->setRange(-2.5, 2.5);
    connect(customPlot->xAxis, SIGNAL(rangeChanged(QCPRange)), customPlot->xAxis2, SLOT(setRange(QCPRange)));
    connect(customPlot->yAxis, SIGNAL(rangeChanged(QCPRange)), customPlot->yAxis2, SLOT(setRange(QCPRange)));
}

void MainWindow::realtimeDataSlot() {
    // Fetch data from the Digilent WaveForms device
    FDwfAnalogInStatus(hdwf, 1, &sts);
    FDwfAnalogInStatusSamplesValid(hdwf, &cValid);
    FDwfAnalogInStatusData(hdwf, 0, rgdSamples.data(), cValid); // Get channel 1 data

    // Convert QVector<double> to QCPGraphDataContainer
    QCPGraphDataContainer dataContainer;
    for (int i = 0; i < rgdSamples.size(); ++i) {
        dataContainer.add(QCPGraphData(i, rgdSamples[i]));
    }

    // Update the plot
    QSharedPointer<QCPGraphDataContainer> dataContainerSharedPointer = QSharedPointer<QCPGraphDataContainer>::create(dataContainer);
    ui->customPlot->graph(0)->setData(dataContainerSharedPointer);
    ui->customPlot->replot();
}

MainWindow::~MainWindow() {
    delete ui;
}

 

I hope this helps! Let me know if you need further details.

[attila]

Hi @fahiz @Fausto

Why are you limited to 0.2 sec ? with 1.5M samples and 1.5MHz capture rate the span in 1sec
If you are interested in peaks you can use min/max sampling mode (FDwfAnalogInChannelFilterSet), less samples and lower frequency.

The sampling rate should be at least 4 times than signal frequency, otherwise you see aliasing.
https://www.ni.com/docs/en-US/bundle/labwindows-cvi/page/advancedanalysisconcepts/aliasing.html

[fahiz]

Hi @attila
Thankyou for your reply.

Actually my goal is to make a GUI it have to continuously plot 1.1 Mhz sine burst mode signal.  So I made a qt gui, and I tried with acqmodescanshift.

    FDwfAnalogInAcquisitionModeSet(hdwf, 1); // acqmodeScanShift
    

In this if I want to increase the time limit, then I have to increase buffer size, so the system is crashing that time.

Can you assist me in finding the best method for continuously plotting a signal, and advise on the logic typically used for continuous plotting?

Thank you.

[attila]

Hi @fahiz

The amount of data may be too much for the graph function used. You may need a different method for drawing.