Plot live data on QtChart

rockon209

Yes i want to use only Qtchart, I havent used QML till now so dont know how it works. How can i plot it in Qtchart?
I want somthing like this just instead of microphone as input i want my sensor as the input see the link below
http://doc.qt.io/qt-5/qtcharts-audio-example.html

jsulm

@rockon209 Then use your sensor as input.

rockon209

@jsulm
Ya that obvious but how i can do that i was not able to pass the values form sensor to QtChart i can read the data from sensor and i am getting it in a varaible now how to pass it to Qtchart?????
For e.g.
read the data and store it in a double variable
double tempSensor= readSignal Sensor(tempChannel);

jsulm

@rockon209 like in the example:

qint64 XYSeriesIODevice::writeData(const char * data, qint64 maxSize)
{
    qint64 range = 2000;
    QVector<QPointF> oldPoints = m_series->pointsVector();
    QVector<QPointF> points;
    int resolution = 4;

    if (oldPoints.count() < range) {
        points = m_series->pointsVector();
    } else {
        for (int i = maxSize/resolution; i < oldPoints.count(); i++)
            points.append(QPointF(i - maxSize/resolution, oldPoints.at(i).y()));
    }

    qint64 size = points.count();
    for (int k = 0; k < maxSize/resolution; k++)
        points.append(QPointF(k + size, ((quint8)data[resolution * k] - 128)/128.0));

    m_series->replace(points);
    return maxSize;
}

in your case instead of char* data you have a double.

rockon209

@jsulm
ya but i was not able to understand the code, what i am doing in my code is i am reading every on second from the sensor and i store it to the variable and then immediately i want to pass it to Qtchart and again read the sensor after one second how i can so it with the above code i new to this data acquisition

jsulm

@rockon209 Change the code from the example, so it matches your requirements:

qint64 XYSeriesIODevice::writeData(const double data, qint64 maxSize)
{
// Adjust here as well as needed
}

Then call writeData every time you get new value from sensor.
To read sensor every second use QTimer.

rockon209

@jsulm
thanks for the reply but i have a question in the above code how the microphone data is pass to this writeData function if const char* data varaible has the info of the microphone data how is it pass to const char* data varaible??? I am not able to understand

jsulm

@rockon209 In the example they implement a device:

m_device = new XYSeriesIODevice(m_series, this);
m_device->open(QIODevice::WriteOnly);

m_audioInput->start(m_device);

XYSeriesIODevice is a QIODevice which is writing incoming char* data to the chart. The data is coming from m_audioInput.
In your case you do not need to implement a device: just use a QTimer to read your sensor each second and write the data to the chart in a similar way as in the example.

rockon209

@jsulm
ok thanks for the explanation
but it is confusing because in XYSeriesIODevice class have m_series as XYseries and widget class has m_series as Qlineseries
and tried your above suggestion i am getting the following error
error: invalid types 'double[int]' for array subscript
points.append(QPointF(k + size, ((quint8)tempSensor[resolution * k] - 128)/128.0));

jsulm

@rockon209 said in Plot live data on QtChart:

QPointF

Can you show the whole method?

rockon209

@jsulm
with timer i call the following function every second
void test:: readTemp()
{
double tempSensor= readSignal Sensor(tempChannel);
writeData();
}
void test::writeData()
{
qint64 range = 2000;
QVector<QPointF> oldPoints = m_series->pointsVector();
QVector<QPointF> points;
int resolution = 4;
qint64 maxSize;

if (oldPoints.count() < range) {
    points = m_series->pointsVector();
} else {
    for (int i = maxSize/resolution; i < oldPoints.count(); i++)
        points.append(QPointF(i - maxSize/resolution, oldPoints.at(i).y()));
}

qint64 size = points.count();

for (int k = 0; k < maxSize/resolution; k++)
    points.append(QPointF(k + size, ((quint8)tempSensor[resolution * k] - 128)/128.0));

m_series->replace(points);

//return maxSize;
}

jsulm

@rockon209 said in Plot live data on QtChart:

double tempSensor= readSignal Sensor(tempChannel);

this is not going to work - you store the temperature in a local variable!

Also, this is wrong if tempSensor isn't an array:

points.append(QPointF(k + size, ((quint8)tempSensor[resolution * k] - 128)/128.0));

As I said you need to adjust the code for your needs...

rockon209

@jsulm
then how to make array as i am reading from the sensor every second and getting only one value.

jsulm

@rockon209 You don't need any array:

void test:: readTemp()
{
writeData( readSignal Sensor(tempChannel));
}

void test::writeData(const double tempSensor)
{
qint64 range = 2000;
QVector<QPointF> oldPoints = m_series->pointsVector();
QVector<QPointF> points;
int resolution = 4;
qint64 maxSize;

if (oldPoints.count() < range) {
    points = m_series->pointsVector();
} else {
    for (int i = maxSize/resolution; i < oldPoints.count(); i++)
        points.append(QPointF(i - maxSize/resolution, oldPoints.at(i).y()));
}

qint64 size = points.count();
points.append(QPointF(k + size, ((quint8)tempSensor - 128)/128.0));
m_series->replace(points);
}

rockon209

@jsulm
i am getting following error and the application is shutting down
terminate called after throwing an instance of 'std::bad_alloc'
what(): std::bad_alloc

jsulm

@rockon209 Please debug you app to see where it crashes...

rockon209

@jsulm
when i read the sensor data it crashes

jsulm

@rockon209 Then find out why and fix it...

rockon209

@jsulm
do you know how maxSize value is calculated because i my code maxsize value is very very very big and in think that is the problem

jsulm

@rockon209 In the code in the example it is passed as parameter:

qint64 XYSeriesIODevice::writeData(const char * data, qint64 maxSize)

In your code you don't assign anything to it so it has arbitrary value.