# Bluetooth LE Audio (Auracast) Transmitter
**Phase:** Proof of Concept (PoC) — Simulation

---

## 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.

---

## System Architecture

```text
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

---

## 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

---

## Setup & Running

### 1. Flash the ESP32

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

```bash
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

```bash
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.

---

## 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`.

---

## LC3 Codec Simulation (Optional)

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

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

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

---

## 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`.

---

## 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
```

---

## Test Examples

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

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

Use [nRF Connect for Mobile](https://www.nordicsemi.com/Products/Development-tools/nRF-Connect-for-mobile) to interact with the running examples from a phone.