Why did you start this project? What do you hope to build?
Manufacturers sell such adapters at outrageous prices (hundreds of dollars). I wanted a way to stream audio to my hearing aids from a PC/laptop without paying an eye watering amount of money.
ASHA is the protocol used by android phones to direct stream audio over Bluetooth LE. The reference source and spec are openly available.
Also, it has been a fun and rewarding challenge.
I haven’t tried to do it in a while, though. I prefer to swap my hearing aids for AirPods when listening to music. It sounds better and they are also easier to pair with multiple devices.
As a possible alternative, I wonder if there’s a good way to route computer audio through your phone?
It is possible to relay audio via a smartphone, I've done this in the past. The main problem is latency. Fine for music, crap for videos.
I also potentially want to use Pico-ASHA for teams calls at work, instead of trying to fit a headset over hearing aids. USB audio means no custom software.
At the end of the day, this is a stop-gap until LE Audio becomes common.
Also, the battery usage is asymmetric, due to the fact that one hearing aid acts as the A2DP sink, and broadcasts audio to the other.