You can find the BT5.0 Audio Pro card on the internet. It is 36x38 mm and has an amazing lot of possibilities. I paid € 4,25 for it.
As I needed to connect my new jackless phone to the old audio system in the workshop, I only wanted the mini jack (to connect the audio system) and the usb for the power supply. The card has three little holes which I used to secure the card to the bottom of the casing. The lid fits neatly but if you foresee rough usage you might want a drop of glue.
The author marked this model as their own original creation.