bluetooth: add rssi property #127
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outfoxxed
requested changes
Jul 17, 2025
outfoxxed
reviewed
Jul 19, 2025
src/bluetooth/device.cpp
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| qint32 BluetoothDevice::signalStrength() const { | ||
| // Convert RSSI (dBm) to a normalized 0-100 scale | ||
| // Based on practical Bluetooth RSSI ranges: | ||
| // -30 to -40 dBm = 85-100 | ||
| // -40 to -55 dBm = 65-85 | ||
| // -55 to -65 dBm = 45-65 | ||
| // -65 to -75 dBm = 25-45 | ||
| // -75 to -85 dBm = 10-25 | ||
| // <= -85 dBm = 0-10 | ||
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| auto rssiValue = this->bRssi.value(); | ||
| if (rssiValue == 0) { | ||
| return 0; | ||
| } | ||
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| auto rssi = std::max(static_cast<qint16>(-100), std::min(static_cast<qint16>(-30), rssiValue)); | ||
| auto normalized = static_cast<qint32>(((rssi + 100) / 70.0) * 100.0); | ||
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| return std::max(0, std::min(100, normalized)); | ||
| } |
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Tbh I'm not sure if this should be linear or not. It requires actual testing at various distances to make sure the number is useful
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I adjusted it, there's no good singular mathematical function I could find to get it as a good representation for display purposes - but I think the numbers are pretty good now.
| dBm | normalized |
|---|---|
| -30 | 100 |
| -35 | 96 |
| -40 | 92 |
| -45 | 88 |
| -50 | 83 |
| -55 | 79 |
| -60 | 75 |
| -65 | 59 |
| -70 | 42 |
| -75 | 26 |
| -80 | 9 |
| -85 | 5 |
| -90 | 0 |
Pretty much anything > -67 is a good signal, anything -80 or below is usually un-usable. 0 is driver reporting no signal data is available for the device (so treating it as effectively 0 normalized)
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Add rssi to bluetooth property bindings. It's useful to see signal strength of devices during discovery (IE, for sorting by signal strength, ignoring very low signal strength devices)
Because rssi is not available when the adapter is no longer discovering I also added a condition to lower the log level on the property update callback for optional properties, it's not really necessary and can be removed - but prevents some log spam when turning off discovery (because the rssi properties become unavailable)