Bluetooth-LE-Audio-Auracast-Transmitter

Bluetooth LE Audio (Auracast) Transmitter

Phase: Proof of Concept (PoC) — Simulation

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Overview

This is a Proof of Concept (PoC) simulation of a Bluetooth Low Energy (LE) Audio Transmitter supporting the Auracast standard. The system runs on an ESP32 acting as both a BLE GATT server and passive BLE scanner, with a Node.js backend bridging serial communication to a browser-based monitoring dashboard. No physical NXH3675 hardware is required in this PoC phase.

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System Architecture

ESP32 (BLE Server + Scanner)
        │ UART Serial (115200 baud, COM8)
        ▼
Node.js Backend (Express + WebSocket + SerialPort)
        │ WebSocket (ws://localhost:8080)
        ▼
Browser Dashboard (index.html)

ESP32 (src/main/main.ino):

• Acts as a BLE GATT server advertising service UUID 4fafc201-1fb5-459e-8fcc-c5c9c331914b
• Scans for nearby BLE devices and collects RSSI, TX power, and name
• Emits newline-delimited JSON events over Serial on connect/disconnect
• Accepts DISCONNECT <connId> commands via Serial input to force-disconnect clients

Node.js Backend (src/web_side/read_serial.js):

• Express server on port 8080 serves the frontend
• WebSocket server relays ESP32 serial data to connected browsers in real time
• Translates browser commands (OPEN_SERIAL, CLOSE_SERIAL, DISCONNECT) to serial writes

Browser Dashboard (src/web_side/index.html):

• Displays connected BLE device cards (MAC, connection ID, interval, latency, timeout)
• Shows a live connection log panel
• Allows force-disconnect of individual clients

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Requirements

• ESP32 board (tested with ESP32-S3)
• ESP-IDF v5.5.1 (or Arduino IDE with ESP32 BLE libraries)
• Node.js v18+
• Python 3 with pyserial and numpy (for LC3 codec simulation only)
• Serial-to-USB cable connecting ESP32 to PC

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Setup & Running

1. Flash the ESP32

Using ESP-IDF (VS Code extension configured for c:\Dev\esp\v5.5.1\esp-idf):

idf.py set-target esp32s3
idf.py -p COM8 flash monitor

Or open src/main/main.ino in Arduino IDE with the ESP32 BLE libraries installed.

2. Start the Node.js Backend

npm install
npm start

The web server starts at http://localhost:8080.

3. Open the Dashboard

Open http://localhost:8080 in your browser (or open src/web_side/index.html directly).

Click Open Port to connect to the ESP32 via serial. BLE device cards will appear when clients connect to the ESP32.

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Serial Port Configuration

The serial port is hardcoded as COM8 in two files — update both when using a different port:

File	Location
src/web_side/read_serial.js	path: "COM8" (line 29)
src/LC3_Codec_Python/testlc3.py	serial.Serial("COM8", 115200)

The VS Code monitor port is set in .vscode/settings.json.

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LC3 Codec Simulation (Optional)

Sends dummy LC3-encoded audio frames to the ESP32 over serial:

cd src/LC3_Codec_Python
pip install pyserial numpy
python testlc3.py

Requires audio.wav (mono, 16-bit PCM) in the same directory.

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JSON Event Protocol

ESP32 emits JSON over serial; Node.js forwards it to the browser via WebSocket.

Status value	Description
NEW_CONNECT	BLE client connected — includes Devices array
DEVICE_DISCONNECTED	A client disconnected — includes updated Devices array
NO_CONNECTED	All clients disconnected

Each device entry contains: connectedID, mac, connInterval, latency, timeout.

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Project Structure

/
├── src/
│   ├── main/main.ino          # ESP32 BLE firmware (Arduino)
│   ├── main.cpp               # ESP32 entry point (ESP-IDF / PlatformIO)
│   ├── web_side/
│   │   ├── read_serial.js     # Node.js serial-to-WebSocket bridge
│   │   └── index.html         # Browser dashboard
│   └── LC3_Codec_Python/
│       └── testlc3.py         # Dummy LC3 audio frame sender
├── test/
│   ├── NimBLE_Beacon/         # Non-connectable beacon example
│   ├── NimBLE_Connection/     # BLE connection + LED example
│   ├── NimBLE_Conn_Disconn/   # Connect/disconnect lifecycle
│   ├── NimBLE_GATT_Server/    # GATT server with heart rate mock
│   └── get_RSSI_Device_Name/  # Arduino scan + RSSI printer
├── docs/                      # Project documentation
├── CMakeLists.txt             # ESP-IDF top-level build file
├── platformio.ini             # PlatformIO config (target: esp32s3usbotg)
└── package.json               # Node.js dependencies

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Test Examples

Each project under test/ is a standalone ESP-IDF application. Build and flash from within its directory:

cd test/NimBLE_GATT_Server
idf.py set-target esp32
idf.py -p <PORT> flash monitor

Use nRF Connect for Mobile to interact with the running examples from a phone.