How to Continuously acquire signal

rockon209

Hello guys I am getting a signal continuously from a USB device. I want to store or display it on screen the whole time untill my program is stopped or someone pushes the stop button how i can do that. I have install the drivers for the device and i can read the signal also but, the problem is when i run my code it read the signal value at that particular time and not for the whole time till the program is stopped. Should i use the while loop and read the signal in this while loop till the program is stopped. Please help. Thanks in advance.

VRonin

@rockon209 said in How to Continuously acquire signal:

Should i use the while loop and read the signal in this while loop till the program is stopped.

No.

Do the reading in a qobject and move that qobject in another thread

Can you show your current code?

rockon209

@VRonin
for example following is the code and i am getting 1000 sample (data) points but i want to all the sample till the program is running

#include <QApplication>
#include <QWidget>
#include <QDebug>

#include <NIDAQmx.h>

int main(int argc, char **argv)
{
    // Initialize a usual Qt application
    QApplication app(argc, argv);
    QWidget w;

    // Initialize DAQmx and read analog input (Copied and simplified from
    // http://www.ni.com/tutorial/5409/en/#toc3 )
    TaskHandle taskHandle = 0;
    int32 samplesReceived = 0;
    float64 data[1000];

    DAQmxCreateTask("MyTask", &taskHandle);
    DAQmxCreateAIVoltageChan(taskHandle, "Dev1/ai0", "", DAQmx_Val_Cfg_Default, -10.0, 10.0, DAQmx_Val_Volts, NULL);
    DAQmxCfgSampClkTiming(taskHandle, "", 10000.0, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps, 1000);
    DAQmxStartTask(taskHandle);
    DAQmxReadAnalogF64(taskHandle, 1000, 10.0, DAQmx_Val_GroupByChannel, data, 1000, &samplesReceived, NULL);
    DAQmxStopTask(taskHandle);
    DAQmxClearTask(taskHandle);

    // Print results
    qDebug() << "Received" << samplesReceived << "points";
    for (int i = 0; i < samplesReceived; ++i)
        qDebug() << data[i];

    // Run Qt event loop
    w.show();
    return app.exec();
}

SGaist

Hi,

Like suggested by @VRonin, encapsulate the DAQmx calls and then you can either use a QTimer to trigger the read at regular interval or a separate thread.

Irshad

You can use the DAQmx API callback to acquire signals, in that way you collect signals every time your data is ready from the DAQ. I wrote a DAQ class to encapsulate all the NI functionality a while back

rockon209

@SGaist @Irshad @VRonin
Actually I am new to Qt. Could you please explain it with an example so that I can understand. I have written DAQmx read/write function in one .cpp file.and will call them when i want to read/write the data. But i dont know how I can read it all the time till the program is running.

VRonin

I do not know how DAQmx works, does it need to call DAQmxCreateTask every time you read or do you create it once and just call DAQmxReadAnalogF64 repeatedly?

rockon209

Hello @VRonin

DAQmxCreateTask has to be call everytime to read the data

VRonin

#include <QObject>
#include <QThread>
#include <QCoreApplication>
#include <atomic>
#include <array>

class DAQmxWorker : public QObject{
    Q_OBJECT
    Q_DISABLE_COPY(DAQmxWorker)
public:
    explicit DAQmxWorker(QObject* parent=Q_NULLPTR)
        :QObject(parent)
    {
        m_continueLoop.store(false);
    }
    Q_SIGNAL void sampleReceived(int32 samplesReceived, const std::array<float64,1000>& data);
    Q_SIGNAL void finished();
    Q_SLOT void execute(){
        m_continueLoop.store(true);
        while(m_continueLoop.load()){
            TaskHandle taskHandle = 0;
            int32 samplesReceived = 0;
            std::array<float64,1000> data;
        
            DAQmxCreateTask("MyTask", &taskHandle);
            DAQmxCreateAIVoltageChan(taskHandle, "Dev1/ai0", "", DAQmx_Val_Cfg_Default, -10.0, 10.0, DAQmx_Val_Volts, NULL);
            DAQmxCfgSampClkTiming(taskHandle, "", 10000.0, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps, 1000);
            DAQmxStartTask(taskHandle);
            DAQmxReadAnalogF64(taskHandle, 1000, 10.0, DAQmx_Val_GroupByChannel, data.data(), 1000, &samplesReceived, NULL);
            DAQmxStopTask(taskHandle);
            DAQmxClearTask(taskHandle);
            sampleReceived(samplesReceived,data); 
            QCoreApplication::processEvents();
        }
        finished();
    }
    Q_SLOT void stop(){
        m_continueLoop.store(false);
    }
private:
    std::atomic_bool m_continueLoop;
};

now you can use it as suggested in the post linked above:

QThread* thread = new QThread;
DAQmxWorker* worker = new DAQmxWorker();
worker->moveToThread(thread);
connect(thread, SIGNAL(started()), worker, SLOT(execute()));
connect(worker, SIGNAL(finished()), thread, SLOT(quit()));
connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
thread->start();

when new data gets read the sampleReceived signal will be emitted and you can connect to it from whatever thread you like.
to stop it just call worker->stop(); from the main thread

rockon209

Hello @VRonin
please have a look at this code i have just entered a while loop and it works fine just to read the data continuously. Is this the right way to do it.?

#include <QApplication>
#include <QWidget>
#include <QDebug>

#include <NIDAQmx.h>

int main(int argc, char **argv)
{
// Initialize a usual Qt application
QApplication app(argc, argv);
QWidget w;
while(true)
{
// Initialize DAQmx and read analog input (Copied and simplified from
// http://www.ni.com/tutorial/5409/en/#toc3 )
TaskHandle taskHandle = 0;
int32 samplesReceived = 0;
float64 data[1000];

DAQmxCreateTask("MyTask", &taskHandle);
DAQmxCreateAIVoltageChan(taskHandle, "Dev1/ai0", "", DAQmx_Val_Cfg_Default, -10.0, 10.0, DAQmx_Val_Volts, NULL);
DAQmxCfgSampClkTiming(taskHandle, "", 10000.0, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps, 1000);
DAQmxStartTask(taskHandle);
DAQmxReadAnalogF64(taskHandle, 1000, 10.0, DAQmx_Val_GroupByChannel, data, 1000, &samplesReceived, NULL);
DAQmxStopTask(taskHandle);
DAQmxClearTask(taskHandle);

// Print results
qDebug() << "Received" << samplesReceived << "points";
for (int i = 0; i < samplesReceived; ++i)
    qDebug() << data[i];

}
// Run Qt event loop
w.show();
return app.exec();
}

VRonin

if you try it you'll see your widget will not show up at all.

I gave you the solution above...

Otherwise (and probably better) see if DAQmx allows to pass a callback function to execute when data is available (something like QIODevice does with the readyRead() signal)

rockon209

@VRonin ya you are right
But I am not able to understand how your logic of QThread is working. Suppose i have a start button and if i press it ,the code(your code) will store the data in an array. Means let say that i have a analog input (room temperature measuring device connected) to the NI device. And I want to check the the temp every one second. So how I can make the logic so that i can measure and display it in the widget.

VRonin

@rockon209 said in How to Continuously acquire signal:

And I want to check the the temp every one second.

This is not continuously acquire data. this is reading every once in a while. You can use a QTimer for that, either in the main thread or the worker object

QTimer updateTimer(1000);
connect(&updateTimer,&QTimer::timeout,[]()->void{
// Initialize DAQmx and read analog input (Copied and simplified from
    // http://www.ni.com/tutorial/5409/en/#toc3 )
    TaskHandle taskHandle = 0;
    int32 samplesReceived = 0;
    float64 data[1000];

    DAQmxCreateTask("MyTask", &taskHandle);
    DAQmxCreateAIVoltageChan(taskHandle, "Dev1/ai0", "", DAQmx_Val_Cfg_Default, -10.0, 10.0, DAQmx_Val_Volts, NULL);
    DAQmxCfgSampClkTiming(taskHandle, "", 10000.0, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps, 1000);
    DAQmxStartTask(taskHandle);
    DAQmxReadAnalogF64(taskHandle, 1000, 10.0, DAQmx_Val_GroupByChannel, data, 1000, &samplesReceived, NULL);
    DAQmxStopTask(taskHandle);
    DAQmxClearTask(taskHandle);

    // Print results
    qDebug() << "Received" << samplesReceived << "points";
    for (int i = 0; i < samplesReceived; ++i)
        qDebug() << data[i];
};)
updateTimer.start();