Qt BLE Discovery Can't Find Some Devices On Windows

Gokhan Bektas

Qt 5.12.5
MSVC2017 32-bit, 64-bit
MSVC2015 32-bit, 64-bit
Windows 10 x64 OS

I have been working on a Windows widgets project with BLE connectivity option. I noticed that Qt Bluetooth examples can't find the particular BLE device that I want to work with.

I tried these examples:

Bluetooth Low Energy Discovery Example
QML Bluetooth Discovery Example
Bluetooth Low Energy Heart Rate Game

These are finding some other BLE devices around but not my device.

I tried to increase the discovery timeout from 5sec to 15sec but it didn't help.
m_deviceDiscoveryAgent->setLowEnergyDiscoveryTimeout(15000);

Microsoft Bluetooth LE Explorer application can discover my device successfully on the same PC.

I tried the Qt and compiler versions listed above on two computers, they both couldn't find my device.

Strangely, I have used Qt for my BLE device last year after some struggle but eventually I had managed to get it to work flawlessly. I don't remember my Qt version at the time.

Currently I am downloading Qt 5.12.2 kit, hoping to fix the issue.

Any ideas?

thanks

Gokhan Bektas

Switching to Qt 5.15.2 made a difference.
Now BLE discovery examples and my previous project can find my custom device.

Unfortunately now I can't connect to the device since QLowEnergyState does not become QLowEnergyService::ServiceDiscovered.

stateChanged signal is emitted but
QLowEnergyService::ServiceState is ending up QLowEnergyService::DiscoveryRequired state. I don't know why but the same code was working on an unknown Qt version as-is.

I am calling discoverDetails when service scan is done.
I can see that my serviceUuid is found and listed by the way.

void myBLE::serviceScanDone()
{

        qDebug()<<"Service Scan Finished";

        static const QString serviceUuid( myUuid );

        m_service = m_control->createServiceObject(QBluetoothUuid(serviceUuid), this);

        connect( m_service , SIGNAL( characteristicChanged(QLowEnergyCharacteristic,QByteArray)),
                 this      , SLOT  ( updateData(QLowEnergyCharacteristic,QByteArray           )) );

        connect( m_service , SIGNAL( stateChanged(QLowEnergyService::ServiceState             )),
                 this      , SLOT  ( serviceStateChanged(QLowEnergyService::ServiceState      )) );

        connect( m_service , SIGNAL( descriptorRead(QLowEnergyDescriptor,QByteArray)),
                 this      , SLOT  ( descriptorRead(QLowEnergyDescriptor,QByteArray)));

        qDebug()<<"Calling discoverDetails()";
        m_service->discoverDetails();

        if ( m_service ) {

              qDebug()<< "DiscoverDetails Service Name : " << m_service->serviceName();
              qDebug()<< "DiscoverDetails Service UUID : " << m_service->serviceUuid();

        }
        else
              qDebug() << "m_service is null";

}

Gokhan Bektas

Here is my debug low; I know it doesn't say much without the entire code.
But it show which functions are called and which signals are fired by BLE Controller.

Service Scan Finished. (QLowEnergyController::discoveryFinished)

Available Services List :  ("{**00001523-1212-efde-1523-785feabcd123**}", "{00001800-0000-1000-8000-00805f9b34fb}", "{00001801-0000-1000-8000-00805f9b34fb}", "{0000180d-0000-1000-8000-00805f9b34fb}")

QLowEnergyService Service Name :  "Unknown Service"
QLowEnergyService Service UUID :  "{**00001523-1212-efde-1523-785feabcd123**}"

Calling discoverDetails()

ServiceState Changed : DiscoveringServices
ServiceState Changed : DiscoveryRequired

ServiceState does not become ServiceDiscovered for some reason.
00001523-1212-efde-1523-785feabcd123 is the service that I want to use by the way.