Bluetooth Battery Monitor

Open source Bluetooth battery monitor for Windows

Enumerating Bluetooth devices and services

I'm not using UWP, only classic C/C++ API (check out misc directory for more C++ examples).

API calls:

• SetupDiGetClassDevs / SetupDiEnumDeviceInfo for getting a list of all bluetooth devices.
• SetupDiGetDeviceRegistryProperty / SPDRP_HARDWAREID for filtering by device address.
• BluetoothGATTGetServices / BluetoothGATTGetCharacteristics for BLE properties.
• SetupDiGetDeviceProperty / DEVPKEY_DeviceContainer_IsConnected for connection status.

UUIDs:

• {e0cbf06c-cd8b-4647-bb8a-263b43f0f974} (Bluetooth Device) for SetupDiGetClassDevs.
• {00001800-0000-1000-8000-00805F9B34FB} (Generic Attribute) for Appearance (0x2A01).
• {0000180F-0000-1000-8000-00805F9B34FB} (Battery Service) for Battery Level (0x2A19).
• {0000180A-0000-1000-8000-00805F9B34FB} (Device Information) for Manufacturer (0x2A29).

Problems and workarounds:

• The program supports only BLE reports for now. Obtaining battery status is easy for BLE, but HID and HFP devices use their own approach (see HID Usage Tables "Battery Strength" and HFPGetBatteryLevel accordingly). HFP devices also expose HID interface, probably it's all doable with HID API or a system-wide dll hook. Will implement later.
• BLUETOOTH_GATT_FLAG_FORCE_READ_FROM_DEVICE (0x00000004) timeouts on disconnected devices, check their status first.
• {00001800-0000-1000-8000-00805F9B34FB} (Generic Attribute) is read only, don't use GENERIC_WRITE in CreateFile.

References

• Simple example (desktop programming C++) for Bluetooth Low Energy devices
• How to get connection status of bluetooth LE device
• Universal Serial Bus (USB) - HID Usage Tables (Hut1_12v2.pdf)
• HANDS-FREE PROFILE 1.5 (HFP 1.5_SPEC_V10.pdf)
• HFPApi: HFPGetBatteryLevel