Overview
The Bluetooth Multi-Speaker System is a portable audio solution enabling smartphone connection via Bluetooth A2DP with simultaneous synchronized sound distribution to 4 independent speakers.
Development in progress: Schematic capture completed, component placement underway before PCB routing phase.
Technical Architecture
Distributed master-slave architecture with 5 ESP32: 1 master (Bluetooth A2DP reception + I2S audio distribution to slaves) and 4 slaves (Bluetooth A2DP transmission to speakers). FreeRTOS firmware with 2 distinct binaries (master/slaves). Embedded microphone system for temporal speaker resynchronization.
[Smartphone] --BT A2DP--> [ESP32 Master]
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+----------I2S------------+-----------+
| | | |
[ESP32-1] [ESP32-2] [ESP32-3] [ESP32-4]
| | | |
--BT A2DP-- --BT A2DP-- --BT A2DP-- --BT A2DP--
| | | |
[Speaker-1] [Spk-2] [Speaker-3] [Spk-4]
Hardware Development
4-layer PCB with ESP32 and external SMA antennas for optimized gain. Li-Ion battery power with power path (use during charging), buck-boost for constant and filtered 3.3V output, USB-C charging. Audio transmitted via Bluetooth A2DP, battery level and configuration via BLE.
Functional prototypes completed: audio transmission, audio reception, and simultaneous TX/RX with 2 ESP32. Power consumption characterization performed on prototypes (IDLE, RX and TX modes).
Objectives and Challenges
Target latency <10ms between speakers. Distributed master-slave architecture: Bluetooth A2DP audio reception on master, redistribution to 4 slaves via I2S, Bluetooth A2DP transmission from each slave to its speaker. Circular buffers for synchronization and embedded microphone for temporal resynchronization. Key learnings: 4-layer PCB design, I2S/Bluetooth A2DP audio streaming, and power management (power path, buck-boost).
Future Enhancements
- OLED display for battery level and connection status
- Mobile application for advanced control (EQ, balance, groups)