Problem with data read from USB port

[VRonin]

the problem is here: serialBuffer += QString::fromStdString(serialData.toStdString());

how does your sensor encode the data?

[pj0909]

@VRonin The sensor is based on capacitive technology. Any change in capacitance gives corresponding values.

[VRonin]

@pj0909 said in Problem with data read from USB port:

values

This still does not answer my question. how are those values represented in binary format to the serial output? is it a 32 bit integer, a 64 bit double precision float, an ASCII encoded string?

[pj0909]

@VRonin Sorry, I misinterpreted your question. The answer to your question is 64 bit double precision float.

[jsulm]

@pj0909 Then you should use http://doc.qt.io/qt-5/qbytearray.html#toDouble without converting to string:

bool ok = false;
serialBuffer += sensor->readAll().toDouble(&ok);
if (!ok) // error

[VRonin]

To add to @jsulm, you should also check that serialData contains 64 and only 64 bits of data (i.e. serialData.size()==8) otherwise use QDataStream

void Dialog::readSerial()
{
QDataStream sensorStream(sensor);
QVector<double> readValues;
for(;;){
sensorStream.startTransaction();
double readValue=0;
sensorStream >> readValue;
if(sensorStream.commitTransaction())
readValues.push_back(readValue);
else
break;
}
qDebug() << "data read: " << readValues;
}

P.S.
If your sensor sends the data in little endian order, you'll have to set the QDataStream byte order http://doc.qt.io/qt-5/qdatastream.html#setByteOrder

[kshegunov]

@pj0909 said in Problem with data read from USB port:

The answer to your question is 64 bit double precision float.

Then you need to read the data as binary, not as text! Something like this (warning: the code isn't really portable):

QDataStream in(&serialData, QIODevice::ReadOnly);

double value;
in >> value;

[pj0909]

I will implement the suggestions in the code and will see the output from the sensor. Will let you all know if its working correctly or still there is a problem. Thank you for the suggestions.

[pj0909]

Finally I solved my problem. I set the floating point precision in addition to the suggestions given above and now I am reading the data as expected.

Thank you all for the suggestions.

[namduc]

Hi all!
I have the same problem, I need to communicate with a USB card reader, but I don't recognize it when i plug it with my PC ( Win 7)
serialportinfo.hasProductIdentifier() and serialportinfo.hasVendorIdentifier() all return false;
Who can help me? Thanks!

[kuzulis]

What's relation between the serial ports and the USB card readers?

[namduc]

Reader Card connect directly to the computer using the USB port
Are there any libraries supporting this?
Thanks!

[aha_1980]

Hi @namduc,

there is exactly one: libusb

Regards