[MTCB Android Head Units Q&A] Jobyteknik:
The MaxxECU uses SPP BT profile so that is good.

I found an old "ANYCOM Bluetooth USB Adapter" I had. Probably way too old and it did not work with that.

Anyway, I installed "USB Host Test" and this is the result without anything in the USB port:

Device: /dev/bus/usb/002/004

Vendor ID: 3034

Product ID: 33142

Manufacturer String Descriptor: Realtek

Product String Descriptor: 802.11n WLAN Adapter

Device Version: 2.0

USB Version: USB 2.0

Class: 0 (See Interface Descriptor for Class)

Sub Class: 0

Protocol: 0

Number of Interfaces: 1

Number of USB Configurations: 1

Max Packet Size: 64

Current Configuration: 1

Max Power: 500mA

Configuration Attributes: 10100000 (Remote WakeUp, Not Self Powered)

-----------------------------

Interface 1

Class: 255 (Vendor Specific Device)

Sub Class: 255

Protocol: 255

Interface ID Number: 0

Number of End Points: 4

EndPoint 1 Direction: IN (Device to Host)

EndPoint 1 Attributes: 00000010 (Bulk Transfer)

EndPoint 1 Max Packet Size: 512

EndPoint 2 Direction: OUT (Host to Device)

EndPoint 2 Attributes: 00000010 (Bulk Transfer)

EndPoint 2 Max Packet Size: 512

EndPoint 3 Direction: OUT (Host to Device)

EndPoint 3 Attributes: 00000010 (Bulk Transfer)

EndPoint 3 Max Packet Size: 512

EndPoint 4 Direction: IN (Device to Host)

EndPoint 4 Attributes: 00000011 (Interupt Transfer, Periodic)

EndPoint 4 Max Packet Size: 64
​

With the USB bluetooth adapter connected I get this:

Device: /dev/bus/usb/002/004

Vendor ID: 3034

Product ID: 33142

Manufacturer String Descriptor: Realtek

Product String Descriptor: 802.11n WLAN Adapter

Device Version: 2.0

USB Version: USB 2.0

Class: 0 (See Interface Descriptor for Class)

Sub Class: 0

Protocol: 0

Number of Interfaces: 1

Number of USB Configurations: 1

Max Packet Size: 64

Current Configuration: 1

Max Power: 500mA

Configuration Attributes: 10100000 (Remote WakeUp, Not Self Powered)

-----------------------------

Interface 1

Class: 255 (Vendor Specific Device)

Sub Class: 255

Protocol: 255

Interface ID Number: 0

Number of End Points: 4

EndPoint 1 Direction: IN (Device to Host)

EndPoint 1 Attributes: 00000010 (Bulk Transfer)

EndPoint 1 Max Packet Size: 512

EndPoint 2 Direction: OUT (Host to Device)

EndPoint 2 Attributes: 00000010 (Bulk Transfer)

EndPoint 2 Max Packet Size: 512

EndPoint 3 Direction: OUT (Host to Device)

EndPoint 3 Attributes: 00000010 (Bulk Transfer)

EndPoint 3 Max Packet Size: 512

EndPoint 4 Direction: IN (Device to Host)

EndPoint 4 Attributes: 00000011 (Interupt Transfer, Periodic)

EndPoint 4 Max Packet Size: 64

Device: /dev/bus/usb/002/005

Vendor ID: 2578

Product ID: 1

Device Version: 5.2.5

USB Version: USB 1.1

Class: 224 (Wireless Controller Device) - Bluetoocth Programming Interface

Sub Class: 1

Protocol: 1

Number of Interfaces: 8

Number of USB Configurations: 1

Max Packet Size: 64

Current Configuration: 9

-----------------------------

Interface 1

Class: 224 (Wireless Controller Device) - Bluetoocth Programming Interface

Sub Class: 1

Protocol: 1

Interface ID Number: 0

Number of End Points: 3

EndPoint 1 Direction: IN (Device to Host)

EndPoint 1 Attributes: 00000011 (Interupt Transfer, Periodic)

EndPoint 1 Max Packet Size: 16

EndPoint 2 Direction: OUT (Host to Device)

EndPoint 2 Attributes: 00000010 (Bulk Transfer)

EndPoint 2 Max Packet Size: 64

EndPoint 2 Direction: IN (Device to Host)

EndPoint 2 Attributes: 00000010 (Bulk Transfer)

EndPoint 2 Max Packet Size: 64

-----------------------------

Interface 2

Class: 224 (Wireless Controller Device) - Bluetoocth Programming Interface

Sub Class: 1

Protocol: 1

Interface ID Number: 1

Number of End Points: 2

EndPoint 3 Direction: OUT (Host to Device)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 0

EndPoint 3 Direction: IN (Device to Host)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 0

-----------------------------

Interface 3

Class: 224 (Wireless Controller Device) - Bluetoocth Programming Interface

Sub Class: 1

Protocol: 1

Interface ID Number: 1

Number of End Points: 2

EndPoint 3 Direction: OUT (Host to Device)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 9

EndPoint 3 Direction: IN (Device to Host)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 9

-----------------------------

Interface 4

Class: 224 (Wireless Controller Device) - Bluetoocth Programming Interface

Sub Class: 1

Protocol: 1

Interface ID Number: 1

Number of End Points: 2

EndPoint 3 Direction: OUT (Host to Device)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 17

EndPoint 3 Direction: IN (Device to Host)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 17

-----------------------------

Interface 5

Class: 224 (Wireless Controller Device) - Bluetoocth Programming Interface

Sub Class: 1

Protocol: 1

Interface ID Number: 1

Number of End Points: 2

EndPoint 3 Direction: OUT (Host to Device)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 25

EndPoint 3 Direction: IN (Device to Host)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 25

-----------------------------

Interface 6

Class: 224 (Wireless Controller Device) - Bluetoocth Programming Interface

Sub Class: 1

Protocol: 1

Interface ID Number: 1

Number of End Points: 2

EndPoint 3 Direction: OUT (Host to Device)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 33

EndPoint 3 Direction: IN (Device to Host)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 33

-----------------------------

Interface 7

Class: 224 (Wireless Controller Device) - Bluetoocth Programming Interface

Sub Class: 1

Protocol: 1

Interface ID Number: 1

Number of End Points: 2

EndPoint 3 Direction: OUT (Host to Device)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 49

EndPoint 3 Direction: IN (Device to Host)

EndPoint 3 Attributes: 00000001 (Isochronous Transfer, No Synchroniization, Data EndPoint)

EndPoint 3 Max Packet Size: 49

-----------------------------

Interface 8

Class: 254 (Application Specific Device)

Sub Class: 1

Protocol: 0

Interface ID Number: 2

Number of End Points: 0
​