Scanning BLE beacons

jenya7

I start a scan

BT_DEVICE::BT_DEVICE()
{
    discoveryAgent = new QBluetoothDeviceDiscoveryAgent();
    discoveryAgent->setLowEnergyDiscoveryTimeout(5000);

    connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::deviceDiscovered, this, &BT_DEVICE::AddDevice);
    connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished, this, &BT_DEVICE::ScanFinished);
}

void BT_DEVICE::BLE_Scan()
{
    qDeleteAll(devices);
    devices.clear();

    discoveryAgent->start(QBluetoothDeviceDiscoveryAgent::LowEnergyMethod);

    if (discoveryAgent->isActive())
    {
        m_deviceScanState = true;
    }
}

Then on deviceDiscovered event I add my remote device to a list

void BT_DEVICE::AddDevice(const QBluetoothDeviceInfo &info)
{
    if (info.coreConfigurations() & QBluetoothDeviceInfo::LowEnergyCoreConfiguration) 
    {
        auto d = new DeviceInfo(info);

        if (d->getName() == "MyDeviceName")
            devices.append(d);
    }
}

Finally on finished event

void BT_DEVICE::ScanFinished()
{
    QVariant dev_list = QVariant::fromValue(devices);
}

But what actually is finished ? Remote devices sends beacons constantly, so as for me it never finished. I should scan it constantly.

sierdzio

@jenya7 said in Scanning BLE beacons:

But what actually is finished ? Remote devices sends beacons constantly, so as for me it never finished. I should scan it constantly.

The scan is done. If you want to scan constantly, run the scan again, with a timer.

jenya7

@sierdzio said in Scanning BLE beacons:

@jenya7 said in Scanning BLE beacons:

But what actually is finished ? Remote devices sends beacons constantly, so as for me it never finished. I should scan it constantly.

The scan is done. If you want to scan constantly, run the scan again, with a timer.

Say I have 10 beacons. I trigger the scan and it gets 5 beacons. Then I trigger again - how can I be sure it scans another 5 and not the same fives?

J.Hilk

@jenya7 said in Scanning BLE beacons:

Say I have 10 beacons. I trigger the scan and it gets 5 beacons. Then I trigger again - how can I be sure it scans another 5 and not the same fives?

no guarantee, the beacons (and other le devices) have to advertise during your scan phase.

The trick is, storing a list of found devices and checking if a new one was added or not

jenya7

@J-Hilk said in Scanning BLE beacons:

@jenya7 said in Scanning BLE beacons:

Say I have 10 beacons. I trigger the scan and it gets 5 beacons. Then I trigger again - how can I be sure it scans another 5 and not the same fives?

no guarantee, the beacons (and other le devices) have to advertise during your scan phase.

The trick is, storing a list of found devices and checking if a new one was added or not

I see. So I have some pain to get all data from all devices. Have to figure it out how to do it.
Another question - how can I iterate all devices

for (int i = 0; i < devices.length(); i++)
{
       devices[i]. //??? it has no name and data field
}

sierdzio

I don't know what your variable devices is, so I can't say.

But you can use discoveredDevices() which returns a QList, so:

for (const auto &device : discoveryAgent->discoveredDevices()) {
  // do something with `device`
}

jsulm

@jenya7 https://doc.qt.io/qt-5/qbluetoothdeviceinfo.html has this.
What is this Device class? Its constructor takes a QBluetoothDeviceInfo instance, so it should have the information...

J.Hilk

@jenya7
usually, you react to the deviceDiscovered signal.
https://doc.qt.io/qt-5/qbluetoothdevicediscoveryagent.html#deviceDiscovered

that has a QBluetoothDeviceInfo argument, make a slot that accepts that as argument.
https://doc.qt.io/qt-5/qbluetoothdeviceinfo.html

I personally have a class an interface class that takes a QBluetoothDeviceInfo as constructor argument, and I store that in a list to iterate over.

jenya7

@jsulm said in Scanning BLE beacons:

@jenya7 https://doc.qt.io/qt-5/qbluetoothdeviceinfo.html has this.
What is this Device class? Its constructor takes a QBluetoothDeviceInfo instance, so it should have the information...

I added it to a list

 if (d->getName() == "MyDeviceName")
            devices.append(d);

How do I retrieve the device data?
No fields like
devices[i].Name
devices[i].Data

sierdzio

It's your custom class of some sort! We can't know how to use a class we don't know :-)

jsulm

@jenya7 said in Scanning BLE beacons:

How do I retrieve the device data?

Why do you ask us?
Device is your class, you did not even show its code - how should we know?!

jsulm

@jenya7 said in Scanning BLE beacons:

if (d->getName() == "MyDeviceName")
devices.append(d);

According to this code you do it this way:

devices[i]->getName();

jenya7

@jsulm said in Scanning BLE beacons:

@jenya7 said in Scanning BLE beacons:

How do I retrieve the device data?

Why do you ask us?
Device is your class, you did not even show its code - how should we know?!

Why? It's Qt class

QBluetoothDeviceInfo &info

Here

void BT_DEVICE::AddDevice(const QBluetoothDeviceInfo &info)
{
    if (info.coreConfigurations() & QBluetoothDeviceInfo::LowEnergyCoreConfiguration) 
    {
        auto d = new DeviceInfo(info);

        if (d->getName() == "MyDeviceName")
            devices.append(d);
    }
}

I see my device name (d->getName() ) so it probably should hold the beacon raw data (like d->data())

sierdzio

@jenya7 said in Scanning BLE beacons:

auto d = new DeviceInfo(info);

DeviceInfo is NOT QBluetoothDeviceInfo. It's some custom class you created. We don't know how to access it.

If you are asking how to get data from info (which is an instance of QBluetoothDeviceInfo), then just read the docs we have already linked: https://doc.qt.io/qt-5/qbluetoothdeviceinfo.html

jenya7

@sierdzio said in Scanning BLE beacons:

@jenya7 said in Scanning BLE beacons:

auto d = new DeviceInfo(info);

DeviceInfo is NOT QBluetoothDeviceInfo. It's some custom class you created. We don't know how to access it.

If you are asking how to get data from info (which is an instance of QBluetoothDeviceInfo), then just read the docs we have already linked: https://doc.qt.io/qt-5/qbluetoothdeviceinfo.html

I see. Yes I use this class (from an example - C:\Qt\Examples\Qt-5.12.0\bluetooth\lowenergyscanner)

class DeviceInfo: public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString deviceName READ getName NOTIFY deviceChanged)
    Q_PROPERTY(QString deviceAddress READ getAddress NOTIFY deviceChanged)
public:
    DeviceInfo() = default;
    DeviceInfo(const QBluetoothDeviceInfo &d);
    QString getAddress() const;
    QString getName() const;
    QBluetoothDeviceInfo getDevice();
    void setDevice(const QBluetoothDeviceInfo &dev);

Q_SIGNALS:
    void deviceChanged();

private:
    QBluetoothDeviceInfo device;
};

So it has

QString DeviceInfo::getName() const
{
    return device.name();
}

What if I want to add

 DeviceInfo::getData() const
{
    return device. //???? - no data field
}

sierdzio

But what data do you want to read? Manufacturer data? Device UUID? Address?

Or you want to read the data that the device is sending? To do that, you need to connect to it first. https://doc.qt.io/qt-5/qtbluetooth-lowenergyscanner-example.html#connecting-to-services

jenya7

This post is deleted!

jenya7

@sierdzio said in Scanning BLE beacons:

But what data do you want to read? Manufacturer data? Device UUID? Address?

Or you want to read the data that the device is sending? To do that, you need to connect to it first. https://doc.qt.io/qt-5/qtbluetooth-lowenergyscanner-example.html#connecting-to-services

OK. I understand. I can use info directly like info.name, but how do I get data (no info.data).
Yes I want to se all beacon raw data - payload. I need no services. It's a remote sensor sending me temperature, humidity, pressure, etc.

J.Hilk

@sierdzio said in Scanning BLE beacons:

Or you want to read the data that the device is sending? To do that, you need to connect to it first. https://doc.qt.io/qt-5/qtbluetooth-lowenergyscanner-example.html#connecting-to-services

not with beacon, beacons are not connectable. And the Qt Api gives no way to identify that.

what the op is looking for should be in
https://doc.qt.io/qt-5/qbluetoothdeviceinfo.html#manufacturerData-1

sierdzio

It's been a long time since I've done it, sorry I don't remember the details. Check the example docs above, it explains how to connect to various services and characteristics, then you can start receiving the data.