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