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-   -   QT - Madde - Accelerometer...help please (https://talk.maemo.org/showthread.php?t=46155)

shep 2010-02-28 23:49
QT - Madde - Accelerometer...help please
 
Hi All,

I'm trying to parse the accelerometer data using QT.

My code looks like this:
Code:
void MainWindow::update_accel()
{

    // read the file /sys/class/i2c-adapter/i2c-3/3-001d/coord

    QFile file("/sys/class/i2c-adapter/i2c-3/3-001d/coord");
    if (!file.open (QIODevice::ReadOnly))
    {
        return;
    }
    else
    {
        QTextStream stream ( &file );
        QString line;
        while( !stream.atEnd() )
        {
            line = stream.readLine();

            ui->label->setText(line);
        }
    }
}
The app just hangs when I call this function and I can't figure out why. I have tried on Windows to use another filename and it works fine...but the app hangs on the N900.

Any clues?

Thanks!

Shep

lpotter 2010-03-01 04:47
Re: QT - Madde - Accelerometer...help please
 
http://doc.trolltech.com/4.6/qfile.html

On Unix, there are some special system files (e.g. in /proc) for which size() will always return 0, yet you may still be able to read more data from such a file; the data is generated in direct response to you calling read(). In this case, however, you cannot use atEnd() to determine if there is more data to read (since atEnd() will return true for a file that claims to have size 0). Instead, you should either call readAll(), or call read() or readLine() repeatedly until no more data can be read.

kunal_the_one 2010-03-01 05:18
Re: QT - Madde - Accelerometer...help please
 
Try following code, it works for me.

static const QString PROC_ENTRY = "/sys/class/i2c-adapter/i2c-3/3-001d/coord";


QFile f(PROC_ENTRY);
if (!f.exists() or !f.open(QIODevice::ReadOnly | QIODevice::Text)) {
qDebug() << "could not read motion data";
}
else {
QByteArray line = f.readLine();
QRegExp rx("([0-9-]+) ([0-9-]+) ([0-9-]+)");

rx.indexIn(line);
qreal x = rx.cap(1).toInt();
qreal y = rx.cap(2).toInt();
qreal z = rx.cap(3).toInt();

mCurrentPos.setX(x);
mCurrentPos.setY(y);

f.close();
}

shep 2010-03-01 12:44
Re: QT - Madde - Accelerometer...help please
 
Quote:
Originally Posted by kunal_the_one (Post 550625)
Try following code, it works for me.
That works great! Thanks a million.

One more question...using a sample rate of 30 times per second I see some "jitter" on all 3-axes ... +/-18?

Is that right? Caused by gravity? Unusual solar flare activity? :D

Shep

raedbenz 2010-07-02 12:50
Re: QT - Madde - Accelerometer...help please
 
http://wiki.forum.nokia.com/index.ph..._N900_using_Qt

shep 2010-07-02 13:26
Re: QT - Madde - Accelerometer...help please
 
Quote:
Originally Posted by raedbenz (Post 738535)
Great article, thanks!


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