Requirements:


- Raspberri Pi 3 B+ (RPi 4 is ok too; however RPi 3 are cheaper).

- https://downloads.raspberrypi.org/raspios_oldstable_armhf/images/raspios_oldstable_armhf-2023-02-22/2023-02-21-raspios-buster-armhf.img.xz
  or
  https://downloads.raspberrypi.org/raspios_armhf/images/raspios_armhf-2023-02-22/2023-02-21-raspios-bullseye-armhf.img.xz

- external USB bluetooth adapter https://www.amazon.com/TP-Link-Bluetooth-Receiver-Controllers-UB400/dp/B07V1SZCY6?th=1
  Probably another external USB adapters are ok (it should be). However we tested with this one only - it is cheap enough.


  
sudo pip3 install rabbitpy sox pydub pyyaml


BT MAC addresses for test phones:

- D0:C5:F3:E0:4E:2D - iPhone BT MAC
- 50:8E:49:EC:B3:A4 - Redmi Note 9T
- A8:96:75:01:AA:57 - Moto G5
- 20:F4:78:63:0E:E5 - Xiaomi 11 5G Lite

Tricks:

- to fix BT error 'Waiting for phone index...' load bluetooth module(s) 
  pacmd load-module module-bluetooth-discover

  This happens on RPi 4 sometimes.


- to avoid ALSA error "device busy" on RPi:

  sudo apt-get install alsa-base
  sudo alsa force-reload

  or (for raspbian)
  sudo /etc/init.d/alsa-utils stop
  sudo alsa force-reload
  (or sudo alsactl kill rescan)
  sudo /etc/init.d/alsa-utils start

- to fix ofono error:
  sudo systemctl restart ofono

- to check if mobile helper app is installed:
  adb shell pm path biz.sevana.qualtestgsm

- to start mobile helper app:
  adb shell am start -n biz.sevana.qualtestgsm/.MainActivity


1. Connect bluetooth to your phone.
  - bluetoothctl
  - power on
  - agent on
  - default-agent
  
  Scan the nearby devices
  - scan on
  
  Once you see your phone device:
  - scan off

  Pair to your phone, remember type "yes" to confirm passkey. And in your phone also.
  - pair 00:D2:79:79:01:89 
  - trust 00:D2:79:79:01:89
  - connect 00:D2:79:79:01:89
  - exit


try
pulseaudio -k
pulseaudio --start

exit from bluetoothctl and start again if BT connection doesn't work