The following is a complete solution for implementing Bluetooth connection and audio transmission on the Baby Sound Module host device:
I. Hardware Requirements
Bluetooth Module Selection
A Bluetooth audio module that supports the A2DP/HFP protocol (such as the ANS-BT301M) must be selected. This module supports the BLE+SPP+audio protocol stack and integrates 10-band EQ.
The module should have an I²S interface to output decoded audio data and be used with an amplifier circuit to drive the speaker.
Power Supply Design
A 3.7V lithium battery is recommended for power supply. The quiescent current should be less than 5μA to extend the battery life of the toy.
II. Host Device Connection Process
Bluetooth Pairing Initialization
After turning on Bluetooth, the host device (phone/tablet) searches for the MA broadcast by the module. C address. The default pairing code is typically "0000" or "1234."
After successful connection, the module indicator will turn solid and a notification tone will play.
Protocol Stack Configuration
A2DP is used to establish the audio transmission link, and AVRCP is used for playback control (pause/skip, etc.).
SBC encoding is recommended for compatibility. If supported by the device, AAC/MP3 can be switched to improve sound quality.
III. Audio Transmission Implementation
Data Stream Processing
The host device compresses the audio file into data packets that comply with the Bluetooth protocol and transmits them over the ACL asynchronous link.
The module receives the data and converts it into a PCM audio signal using the LC3 or SBC decoder.
Latency Optimization
Enabling aptX LL coding reduces end-to-end latency to under 40ms, making it suitable for interactive toys. Disabling DSP audio processing can reduce additional latency by 20-30ms.
IV. Stability Measures
Anti-interference Design
Uses Bluetooth 5.0+'s FHSS frequency hopping technology (1600 channel changes per second) to reduce interference in the 2.4GHz band.
The module firmware should implement an automatic reconnection mechanism to resume playback within 10 seconds after a disconnection.
Multi-device Management
The module can store up to eight paired devices and supports simultaneous connection to two master devices (single-device playback only). Connection priority can be visually managed using the Bose Connect app.
This solution has been used in products such as the Musical Panda Plush, with a measured transmission distance of up to 15 meters (in an accessible environment).
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