How Bluetooth headphones work - making custom headphones

making custom headphones manufacturers believe that Bluetooth is a short-distance wireless communication technology that replaces data cables, and realizes point-to-point or point-to-multipoint communication of information through low-bandwidth radio waves.

making custom headphones manufacturers believe that Bluetooth transmission of audio streams can be done in two ways:

1. Through the PCM interface, open the audio file through the audio player (eg: Media Player), call the Audio driver, and after the audio file is decoded, it is output from the PCM to the PCM input of the Host Bluetooth module, and then through the Bluetooth module After processing, the RF wireless module sends it to the Bluetooth device on the Client side. After the Bluetooth device on the Client side passes through the wireless receiving module, it is filtered, stabilized, processed by the micro-processing chip, and directly played by the Speaker.

2. Transmit by simulating UART. Set the registry [HKEY_LOCAL_MACHINE\Services\BTAGSVC] IsEnabled = 1 to automatically load the voice gateway (AG) service when the system boots. First, establish the ACL link between the Host side Bluetooth device and the Client side Bluetooth device (connectionless asynchronous link) through manual configuration, and then call _AG_OPEN_AUDIO in Applicaiton or Audio Driver to re-establish the Host side Bluetooth device and the Client side Bluetooth device SCO Link (connection-oriented synchronization link), then AG automatically sends waveOutMessage((HWAVEOUT)i, WODM_BT_SCO_AUDIO_CONTROL, 0, TRUE); making custom headphones manufacturers believe that the channel between Audio and Bluetooth chip is established, that is, audio is realized Stream transmission to the Bluetooth module. Then, the audio stream is packaged and sent via the RF module via the host-side Bluetooth module.

After the client bluetooth headphones receives the wireless audio package, it is filtered, stabilized, processed by the micro-processing chip, and then transmitted to the audio codec chip by the PCM, and finally played by the Speaker.