Read string from a bluetooth device through serial port in Hololens 2 [Unity C#]

Question

I need to receive a string from an inertial sensor paired via bluetooth to a Hololens 2. I´m able to connect the sensor in the configuration menu of HoloLens, the problem comes when trying to use serial port to receive data in Unity developed app.

I have managed to stablish a connection and receive the data using the System.IO.Ports.SerialPort class ( https://docs.microsoft.com/es-es/dotnet/api/system.io.ports.serialport?view=dotnet-plat-ext-5.0 ) in the Unity Editor. The problem comes when trying to stablish that same connection in the HoloLens, after some research I found out that System.IO.Ports.SerialPort class can´t be used in UWP apps, so I´m trying to use the Windows.Devices.SerialCommunication.SerialDevice class ( https://docs.microsoft.com/en-us/uwp/api/windows.devices.serialcommunication.serialdevice?view=winrt-19041 ). This is the piece of code that should stablish the connection, I´m using it in the Awake function of my script:

async void openConnection()
    {
#if !UNITY_EDITOR
        await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(
  Windows.UI.Core.CoreDispatcherPriority.Normal, async () =>
  {
      try
      {
                DeviceInformationCollection serialDeviceInfos = await DeviceInformation.FindAllAsync(SerialDevice.GetDeviceSelector());

                if (serialDeviceInfos != null){

                    foreach (DeviceInformation serialDeviceInfo in serialDeviceInfos){

                        SerialDevice serialDevice = await SerialDevice.FromIdAsync(serialDeviceInfo.Id);

                        if (serialDevice != null)
                        {
                            // Found a valid serial device.
                            // Reading a byte from the serial device.
                            DataReader dr = new DataReader(serialDevice.InputStream);
                            string drData = dr.ReadString(60);
                        
                            estadoSensor.text = drData;
                        }

                }   }
      }
      catch (Exception ex)
      {
          estadoSensor.text = ex.ToString();
          System.Diagnostics.Debug.WriteLine(ex);
      }
   });
#endif 
    }

When calling the method SerialDevice.FromIdAsync(), even if serialDeviceInfo.Id is not null, the method throws a System.Exception type exception, which if I´m not wrong, it couldn´t be more generic. As you can see, I´m trying to call the method on the UI thread, because I´ve read that otherwise it won´t work, but even doing that, it is not working for me ( https://forum.unity.com/threads/hololens-device-permission-dialog-for-rfcomm-bluetooth-serial-port.513666/ ).

I have also added this piece of code to the package.appxmanifest file generated after building for UWP in the Unity Editor, in theory it should enable the serialcommunication capability

    <DeviceCapability Name="serialcommunication">
        <Device Id="any">
            <Function Type="name:serialPort" />
        </Device>
    </DeviceCapability>

I hope I´ve managed to explain my problem properly.

Thanks in advance!

Answer 1

Bluetooth SerialPort can't work on HoloLens 2, because the HoloLens 2 device does not have the specific drivers installed for the sensor to do this via serial port connected. Besides, it is recommended you work with RFCOMM, more information please see: https://docs.microsoft.com/en-us/windows/uwp/devices-sensors/send-or-receive-files-with-rfcomm