what does the rssi of bluetoothdeviceinfo mean

[Mihan]

Hi
I want to know how should I understand the rssi value. It's qint16. Does the value show me the signal strength like -100 dbm -> rssi() == -100?
Regards
Mihan

[jsulm]

@Mihan Maybe this explains https://www.bluetooth.com/blog/proximity-and-rssi/

[Mihan]

@jsulm So what are the range of rssi about good signal and no good signal

[jsulm]

@Mihan According to the article I provided above this is not standardised. Also you should maybe ask in some other forum more related to Bluetooth.

[Mihan]

@jsulm But why I always get the rssi zero after scanning? How to get the true rssi?

[jsulm]

@Mihan said in what does the rssi of bluetoothdeviceinfo mean:

But why I always get the rssi zero after scanning?

That you did not say before.
Can you show how you're scanning?

[Mihan]

@jsulm
This code is used on Qt 5.6.2, so it doesn't have QBluetoothDeviceDiscoveryAgent::deviceUpdated()

CBluetoothManager::CBluetoothManager()
{
    m_BluetoothLocalDevice = new QBluetoothLocalDevice(this);
    m_BluetoothLocalDevice->powerOn();
    m_BluetoothLocalDevice->setHostMode(QBluetoothLocalDevice::HostConnectable);

    m_BluetoothScanner = new QBluetoothDeviceDiscoveryAgent(this);
    connect(m_BluetoothScanner,SIGNAL(finished()),this,SLOT(BluetoothScanFinished()));
}

CBluetoothManager::BluetoothScanFinished()
{
    auto list = m_BluetoothScanner->discoveredDevices();

    for(int n = 0; n < list.count(); n++)
    {
          // add items into QTableWidget (QString is name, QIcon is signal strength) 
    }
}

[jsulm]

@Mihan said in what does the rssi of bluetoothdeviceinfo mean:

Qt 5.6.2

You should really at least try with a more recent Qt version.

[Mihan]

@jsulm but the system root provided by the main board supplier (based on freescale(NXP)) is Qt 5.6.2 . Is there something wrong in Qt5.6.2? Because the connection of bluetooth (QBluetoothLocalDevice::requestPairing(...)) also doesn't work in this version until Qt5.12.0.
I had tested it. It seem to have some problems between the bluetooth protocol(Bluez) and this function.

[jsulm]

@Mihan said in what does the rssi of bluetoothdeviceinfo mean:

Is there something wrong in Qt5.6.2?

It is possible that some Bluetooth related issues where fixed since Qt5.6.2

[Mihan]

@jsulm Okay now I use Qt 5.12.0 to complie, it works. But I still don't know how to use these rssi(),all are 127 I received. It seems that this rssi() is different from the bluetooth's rssi(e.g. -65dbm).
In other words, what's the unit of this rssi();

Also, I find that the bin of 127 is 0111 1111. Does Qt use each bit to signify the signal strength?

[jsulm]

@Mihan As explained in the link I posted before there is no standardised unit for this. It just indicates whether the signal is getting stronger (higher values) or weaker (lower values).

[Mihan]

@jsulm Oh, I didn't notice that the example the link said "For example, Manufacturer A could have an RSSI max value of 100 while Manufacturer B will return RSSI values anywhere from 0 to 127. "

So,maybe rssi() == 127 means this signal is the best.

Thank you so much!