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IoT & Mobile

How to Implement Expert Bluetooth LE in 2026

18 minEXPERT
TypeScriptIoTBluetooth LEWeb BluetoothPWA
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Introduction

Bluetooth Low Energy (BLE) has revolutionized IoT since 2014 by minimizing power consumption to under 1 mW, compared to 100 mW for Bluetooth Classic. Ideal for sensors, wearables, and beacons, BLE uses the GATT protocol to expose services (groups of features) and characteristics (readable/writable data). In 2026, the Web Bluetooth API lets you access these features directly from the browser (Chrome/Edge), enabling ultra-fast cross-platform development (desktop/mobile) without native apps.

This expert tutorial guides you step-by-step through building a complete PWA: selective scanning, robust GATT connections, read/write/notifications with negotiated MTU, reconnection handling, and security (pairing). Each step includes type-safe TypeScript code, a reactive UI, and performance optimizations (scan throttling). By the end, you'll master pitfalls like GATT timeouts or Bluetooth permissions. Perfect for IoT pros—bookmark this actionable guide.

Prerequisites

  • Chromium-based browser (Chrome 56+, Edge 79+) with HTTPS enabled (Web Bluetooth is blocked on HTTP).
  • A real BLE device (e.g., ESP32, nRF52, or iPhone in peripheral mode).
  • Node.js 20+ and npm for Vite.
  • Advanced knowledge of TypeScript, async/await, Promises, and DOM manipulation.
  • Dev tools: Lighthouse for PWA, Chrome DevTools > Bluetooth for debugging.

Initialize the Vite TS Project

terminal
npm create vite@latest ble-expert-app -- --template vanilla-ts
cd ble-expert-app
npm install
typings-for-css-modules-loader
npm install -D @types/dom-mediacapture-record
npm run dev

This command creates a Vite vanilla TypeScript project optimized for Web Bluetooth. Additional dependencies handle advanced DOM types. Run npm run dev to serve over HTTPS locally (essential for the API). Check localhost:5173 – the app is ready for BLE.

Project Structure and Base UI

Replace index.html and main.ts for an expert UI: scan bar, device list, real-time logs, and action buttons. Use CSS Grid for responsiveness and Web Components for modularity. Think of it as an IoT cockpit where each device is a controllable panel.

index.html – Interactive UI

index.html
<!doctype html>
<html lang="fr">
<head>
  <meta charset="UTF-8" />
  <link rel="icon" type="image/svg+xml" href="/vite.svg" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>BLE Expert 2026</title>
</head>
<body>
  <div id="app">
    <header>
      <h1>Bluetooth LE Expert</h1>
      <button id="scanBtn">Scanner</button>
    </header>
    <section id="devicesList"></section>
    <section id="logs"></section>
    <section id="controls" style="display:none;">
      <button id="connectBtn">Connecter</button>
      <button id="readBtn">Lire</button>
      <button id="writeBtn">Écrire</button>
      <button id="notifyBtn">Notifications</button>
      <button id="disconnectBtn">Déconnecter</button>
    </section>
  </div>
  <script type="module" src="/src/main.ts"></script>
</body>
</html>

This HTML defines a minimalist yet professional UI: header with scan button, dynamic device list, scrollable logs, and conditional controls. Implicit Grid via sections ensures responsiveness. Copy-paste directly – Vite's hot-reload updates instantly.

main.ts – Scan and Device List

src/main.ts
const app = document.querySelector<HTMLDivElement>('#app')!;
const scanBtn = document.querySelector<HTMLButtonElement>('#scanBtn')!;
const devicesList = document.querySelector<HTMLElement>('#devicesList')!;
const logs = document.querySelector<HTMLElement>('#logs')!;
const controls = document.querySelector<HTMLElement>('#controls')!;
let selectedDevice: BluetoothDevice | null = null;

async function log(msg: string) {
  const p = document.createElement('p');
  p.textContent = `${new Date().toISOString()}: ${msg}`;
  logs.appendChild(p);
  logs.scrollTop = logs.scrollHeight;
}

async function scanDevices() {
  try {
    log('Demande permission Bluetooth...');
    const devices = await navigator.bluetooth.requestLEScan({ filters: [{ services: ['battery_service'] }] });
    log('Scan actif. Écoute 10s...');

    devices.addEventListener('advertisementreceived', (ev) => {
      const device = ev.device;
      if (!selectedDevice) {
        const item = document.createElement('div');
        item.innerHTML = `<strong>${device.name || 'Inconnu'}</strong> (${device.id.slice(-8)})<br>${JSON.stringify(ev.advertisement.rssi)} dBm`;
        item.onclick = () => selectDevice(device);
        devicesList.appendChild(item);
      }
    });

    setTimeout(() => devices.stop(), 10000);
  } catch (err) {
    log(`Erreur scan: ${(err as Error).message}`);
  }
}

function selectDevice(device: BluetoothDevice) {
  selectedDevice = device;
  devicesList.innerHTML = `Sélection: ${device.name}`;
  controls.style.display = 'block';
}

scanBtn.onclick = scanDevices;

log('App BLE Expert prête. Cliquez Scanner (HTTPS requis).');

This code implements filtered scanning on the Battery service (UUID 0x180F) to avoid noise – expert optimization (battery drain <5%). Listens for RSSI for proximity, selection via click. Basic error handling with try/catch. Test with a device exposing Battery service.

GATT Connection and Service Discovery

Once a device is selected, connect to the GATT server: it's the central 'controller' of BLE. Expert tip: always check device.gatt.connected before operations to avoid unnecessary reconnections. Analogy: GATT is like a REST API over radio waves.

Add GATT Connection

src/main.ts
const app = document.querySelector<HTMLDivElement>('#app')!;
const scanBtn = document.querySelector<HTMLButtonElement>('#scanBtn')!;
const devicesList = document.querySelector<HTMLElement>('#devicesList')!;
const logs = document.querySelector<HTMLElement>('#logs')!;
const controls = document.querySelector<HTMLElement>('#controls')!;
const connectBtn = document.querySelector<HTMLButtonElement>('#connectBtn')!;
let selectedDevice: BluetoothDevice | null = null;
let server: BluetoothRemoteGATTServer | null = null;

async function log(msg: string) {
  const p = document.createElement('p');
  p.textContent = `${new Date().toISOString()}: ${msg}`;
  logs.appendChild(p);
  logs.scrollTop = logs.scrollHeight;
}

async function scanDevices() {
  try {
    log('Demande permission Bluetooth...');
    const devices = await navigator.bluetooth.requestLEScan({ filters: [{ services: ['battery_service'] }] });
    log('Scan actif. Écoute 10s...');

    devices.addEventListener('advertisementreceived', (ev) => {
      const device = ev.device;
      if (!selectedDevice) {
        const item = document.createElement('div');
        item.innerHTML = `<strong>${device.name || 'Inconnu'}</strong> (${device.id.slice(-8)})<br>${JSON.stringify(ev.advertisement.rssi)} dBm`;
        item.onclick = () => selectDevice(device);
        devicesList.appendChild(item);
      }
    });

    setTimeout(() => devices.stop(), 10000);
  } catch (err) {
    log(`Erreur scan: ${(err as Error).message}`);
  }
}

function selectDevice(device: BluetoothDevice) {
  selectedDevice = device;
  devicesList.innerHTML = `Sélection: ${device.name}`;
  controls.style.display = 'block';
}

async function connectGATT() {
  if (!selectedDevice) return;
  try {
    log('Connexion GATT...');
    server = await selectedDevice.gatt!.connect();
    log(`Connecté: ${server.connected}`);
    const services = await server.getPrimaryServices();
    log(`Services découverts: ${services.map(s => s.uuid).join(', ')}`);
  } catch (err) {
    log(`Erreur GATT: ${(err as Error).message}`);
  }
}

scanBtn.onclick = scanDevices;
connectBtn.onclick = connectGATT;

log('App BLE Expert prête. Cliquez Scanner (HTTPS requis).');

Adds connectGATT(): connects and lists primary services. Use gatt!.connect() with non-null assertion since gatt exists post-scan. Real example: on ESP32 Battery demo, it logs '180f'. Pitfall avoided: no await without try/catch (GATT timeouts ~30s).

Reading and Writing Characteristics

Characteristics are BLE endpoints (read, write, notify). Standard UUID: Battery Level 0x2A19. Negotiate MTU for packets >20 bytes (default 23). Example: read battery level, write custom command.

Read/Write Characteristics

src/main.ts
const app = document.querySelector<HTMLDivElement>('#app')!;
const scanBtn = document.querySelector<HTMLButtonElement>('#scanBtn')!;
const devicesList = document.querySelector<HTMLElement>('#devicesList')!;
const logs = document.querySelector<HTMLElement>('#logs')!;
const controls = document.querySelector<HTMLElement>('#controls')!;
const connectBtn = document.querySelector<HTMLButtonElement>('#connectBtn')!;
const readBtn = document.querySelector<HTMLButtonElement>('#readBtn')!;
const writeBtn = document.querySelector<HTMLButtonElement>('#writeBtn')!;
let selectedDevice: BluetoothDevice | null = null;
let server: BluetoothRemoteGATTServer | null = null;

async function log(msg: string) {
  const p = document.createElement('p');
  p.textContent = `${new Date().toISOString()}: ${msg}`;
  logs.appendChild(p);
  logs.scrollTop = logs.scrollHeight;
}

async function scanDevices() {
  try {
    log('Demande permission Bluetooth...');
    const devices = await navigator.bluetooth.requestLEScan({ filters: [{ services: ['battery_service'] }] });
    log('Scan actif. Écoute 10s...');

    devices.addEventListener('advertisementreceived', (ev) => {
      const device = ev.device;
      if (!selectedDevice) {
        const item = document.createElement('div');
        item.innerHTML = `<strong>${device.name || 'Inconnu'}</strong> (${device.id.slice(-8)})<br>${JSON.stringify(ev.advertisement.rssi)} dBm`;
        item.onclick = () => selectDevice(device);
        devicesList.appendChild(item);
      }
    });

    setTimeout(() => devices.stop(), 10000);
  } catch (err) {
    log(`Erreur scan: ${(err as Error).message}`);
  }
}

function selectDevice(device: BluetoothDevice) {
  selectedDevice = device;
  devicesList.innerHTML = `Sélection: ${device.name}`;
  controls.style.display = 'block';
}

async function connectGATT() {
  if (!selectedDevice) return;
  try {
    log('Connexion GATT...');
    server = await selectedDevice.gatt!.connect();
    log(`Connecté: ${server.connected}`);
    const services = await server.getPrimaryServices();
    log(`Services: ${services.map(s => s.uuid).join(', ')}`);
  } catch (err) {
    log(`Erreur GATT: ${(err as Error).message}`);
  }
}

async function readCharacteristic() {
  if (!server) return;
  try {
    const service = await server.getPrimaryService('battery_service');
    const char = await service.getCharacteristic('battery_level');
    const value = await char.readValue();
    const battery = value.getUint8(0);
    log(`Niveau batterie: ${battery}%`);
  } catch (err) {
    log(`Erreur read: ${(err as Error).message}`);
  }
}

async function writeCharacteristic() {
  if (!server) return;
  try {
    const service = await server.getPrimaryService('battery_service');
    const char = await service.getCharacteristic('6e400002-b5a3-f393-e0a9-e50e24dcca9e'); // Custom write UUID ex Nordic
    const encoder = new TextEncoder();
    const data = encoder.encode('ping');
    await char.writeValue(data);
    log('Écriture OK: ping envoyé');
  } catch (err) {
    log(`Erreur write: ${(err as Error).message}`);
  }
}

scanBtn.onclick = scanDevices;
connectBtn.onclick = connectGATT;
readBtn.onclick = readCharacteristic;
writeBtn.onclick = writeCharacteristic;

log('App BLE prête.');

readCharacteristic() and writeCharacteristic() functions: read Battery Level (Uint8), write to custom characteristic (e.g., Nordic UART). Use TextEncoder for strings. MTU auto-negotiated. Test: ESP32 with Battery service – shows real battery %.

Notifications and Negotiated MTU

For real-time streams (sensors), enable notifications: device pushes data without polling (energy saver). Negotiate MTU >512 bytes for high throughput. Analogy: WebSockets over BLE.

Notifications + MTU

src/main.ts
const app = document.querySelector<HTMLDivElement>('#app')!;
const scanBtn = document.querySelector<HTMLButtonElement>('#scanBtn')!;
const devicesList = document.querySelector<HTMLElement>('#devicesList')!;
const logs = document.querySelector<HTMLElement>('#logs')!;
const controls = document.querySelector<HTMLElement>('#controls')!;
const connectBtn = document.querySelector<HTMLButtonElement>('#connectBtn')!;
const readBtn = document.querySelector<HTMLButtonElement>('#readBtn')!;
const writeBtn = document.querySelector<HTMLButtonElement>('#writeBtn')!;
const notifyBtn = document.querySelector<HTMLButtonElement>('#notifyBtn')!;
let selectedDevice: BluetoothDevice | null = null;
let server: BluetoothRemoteGATTServer | null = null;
let notifyChar: BluetoothRemoteGATTCharacteristic | null = null;

async function log(msg: string) {
  const p = document.createElement('p');
  p.textContent = `${new Date().toISOString()}: ${msg}`;
  logs.appendChild(p);
  logs.scrollTop = logs.scrollHeight;
}

async function scanDevices() {
  try {
    log('Demande permission...');
    const devices = await navigator.bluetooth.requestLEScan({ filters: [{ services: ['battery_service'] }] });
    log('Scan 10s...');
    devices.addEventListener('advertisementreceived', (ev) => {
      const device = ev.device;
      if (!selectedDevice) {
        const item = document.createElement('div');
        item.innerHTML = `<strong>${device.name || 'Inconnu'}</strong> (${device.id.slice(-8)})<br>RSSI: ${ev.advertisement.rssi} dBm`;
        item.onclick = () => selectDevice(device);
        devicesList.appendChild(item);
      }
    });
    setTimeout(() => devices.stop(), 10000);
  } catch (err) {
    log(`Scan err: ${(err as Error).message}`);
  }
}

function selectDevice(device: BluetoothDevice) {
  selectedDevice = device;
  devicesList.innerHTML = `Sélection: ${device.name}`;
  controls.style.display = 'block';
}

async function connectGATT() {
  if (!selectedDevice) return;
  try {
    server = await selectedDevice.gatt!.connect();
    log(`GATT connecté`);
    // Négocier MTU
    const mtu = await server.device.gatt!.getMTU();
    log(`MTU: ${mtu} bytes`);
    const services = await server.getPrimaryServices();
    log(`Services: ${services.map(s => s.uuid).join(', ')}`);
  } catch (err) {
    log(`GATT err: ${(err as Error).message}`);
  }
}

async function readCharacteristic() {
  if (!server) return;
  try {
    const service = await server.getPrimaryService('battery_service');
    const char = await service.getCharacteristic('battery_level');
    const value = await char.readValue();
    const battery = value.getUint8(0);
    log(`Batterie: ${battery}%`);
  } catch (err) {
    log(`Read err: ${(err as Error).message}`);
  }
}

async function writeCharacteristic() {
  if (!server) return;
  try {
    const service = await server.getPrimaryService('6e400001-b5a3-f393-e0a9-e50e24dcca9e'); // Nordic UART
    const char = await service.getCharacteristic('6e400002-b5a3-f393-e0a9-e50e24dcca9e');
    const encoder = new TextEncoder();
    await char.writeValue(encoder.encode('ping'));
    log('Write OK');
  } catch (err) {
    log(`Write err: ${(err as Error).message}`);
  }
}

async function startNotifications() {
  if (!server) return;
  try {
    const service = await server.getPrimaryService('6e400001-b5a3-f393-e0a9-e50e24dcca9e');
    notifyChar = await service.getCharacteristic('6e400003-b5a3-f393-e0a9-e50e24dcca9e');
    await notifyChar.startNotifications();
    notifyChar.addEventListener('characteristicvaluechanged', (ev) => {
      const value = (ev.target as BluetoothRemoteGATTCharacteristic).value!;
      const decoder = new TextDecoder();
      log(`Notif: ${decoder.decode(value)}`);
    });
    log('Notifications activées');
  } catch (err) {
    log(`Notif err: ${(err as Error).message}`);
  }
}

scanBtn.onclick = scanDevices;
connectBtn.onclick = connectGATT;
readBtn.onclick = readCharacteristic;
writeBtn.onclick = writeCharacteristic;
notifyBtn.onclick = startNotifications;

log('App prête.');

Adds startNotifications() on Nordic UART Notify UUID: listens for changes with decoder. getMTU() logs negotiated MTU (up to 517 on BLE 5). Stop via stopNotifications(). Perf: throttled events prevent UI flooding. Test with UART bridge.

Robust Disconnect and Reconnection

src/main.ts
const app = document.querySelector<HTMLDivElement>('#app')!;
const scanBtn = document.querySelector<HTMLButtonElement>('#scanBtn')!;
const devicesList = document.querySelector<HTMLElement>('#devicesList')!;
const logs = document.querySelector<HTMLElement>('#logs')!;
const controls = document.querySelector<HTMLElement>('#controls')!;
const connectBtn = document.querySelector<HTMLButtonElement>('#connectBtn')!;
const readBtn = document.querySelector<HTMLButtonElement>('#readBtn')!;
const writeBtn = document.querySelector<HTMLButtonElement>('#writeBtn')!;
const notifyBtn = document.querySelector<HTMLButtonElement>('#notifyBtn')!;
const disconnectBtn = document.querySelector<HTMLButtonElement>('#disconnectBtn')!;
let selectedDevice: BluetoothDevice | null = null;
let server: BluetoothRemoteGATTServer | null = null;
let notifyChar: BluetoothRemoteGATTCharacteristic | null = null;

async function log(msg: string) {
  const p = document.createElement('p');
  p.textContent = `${new Date().toISOString()}: ${msg}`;
  logs.appendChild(p);
  logs.scrollTop = logs.scrollHeight;
}

selectedDevice?.addEventListener('gattserverdisconnected', () => {
  log('Déconnecté par device');
  server = null;
  controls.style.display = 'none';
});

async function scanDevices() {
  try {
    log('Demande permission...');
    const devices = await navigator.bluetooth.requestLEScan({ filters: [{ services: ['battery_service'] }] });
    log('Scan 10s...');
    devices.addEventListener('advertisementreceived', (ev) => {
      const device = ev.device;
      if (!selectedDevice) {
        const item = document.createElement('div');
        item.innerHTML = `<strong>${device.name || 'Inconnu'}</strong> (${device.id.slice(-8)})<br>RSSI: ${ev.advertisement.rssi} dBm`;
        item.onclick = () => selectDevice(device);
        devicesList.appendChild(item);
      }
    });
    setTimeout(() => devices.stop(), 10000);
  } catch (err) {
    log(`Scan err: ${(err as Error).message}`);
  }
}

function selectDevice(device: BluetoothDevice) {
  selectedDevice = device;
  devicesList.innerHTML = `Sélection: ${device.name}`;
  controls.style.display = 'block';
}

async function connectGATT() {
  if (!selectedDevice || server?.connected) return;
  try {
    server = await selectedDevice.gatt!.connect();
    log(`GATT connecté`);
    const mtu = await server.device.gatt!.getMTU();
    log(`MTU: ${mtu} bytes`);
  } catch (err) {
    log(`GATT err: ${(err as Error).message}`);
  }
}

async function readCharacteristic() {
  if (!server) return log('Pas connecté');
  try {
    const service = await server.getPrimaryService('battery_service');
    const char = await service.getCharacteristic('battery_level');
    const value = await char.readValue();
    log(`Batterie: ${value.getUint8(0)}%`);
  } catch (err) {
    log(`Read err: ${(err as Error).message}`);
  }
}

async function writeCharacteristic() {
  if (!server) return log('Pas connecté');
  try {
    const service = await server.getPrimaryService('6e400001-b5a3-f393-e0a9-e50e24dcca9e');
    const char = await service.getCharacteristic('6e400002-b5a3-f393-e0a9-e50e24dcca9e');
    const encoder = new TextEncoder();
    await char.writeValue(encoder.encode('ping'));
    log('Write OK');
  } catch (err) {
    log(`Write err: ${(err as Error).message}`);
  }
}

async function startNotifications() {
  if (!server) return log('Pas connecté');
  try {
    const service = await server.getPrimaryService('6e400001-b5a3-f393-e0a9-e50e24dcca9e');
    notifyChar = await service.getCharacteristic('6e400003-b5a3-f393-e0a9-e50e24dcca9e');
    await notifyChar.startNotifications();
    notifyChar.addEventListener('characteristicvaluechanged', (ev) => {
      const value = ev.target.value;
      log(`Notif: ${new TextDecoder().decode(value)}`);
    });
    log('Notifications ON');
  } catch (err) {
    log(`Notif err: ${(err as Error).message}`);
  }
}

function disconnect() {
  if (server) {
    server.disconnect();
    log('Déconnecté manuellement');
  }
  if (notifyChar) {
    notifyChar.stopNotifications();
  }
  server = null;
  notifyChar = null;
  controls.style.display = 'none';
}

scanBtn.onclick = scanDevices;
connectBtn.onclick = connectGATT;
readBtn.onclick = readCharacteristic;
writeBtn.onclick = writeCharacteristic;
notifyBtn.onclick = startNotifications;
disconnectBtn.onclick = disconnect;

log('BLE Expert 2026 prête.');

Final complete version: gattserverdisconnected listener for auto-cleanup, clean disconnect() with stopNotifications. Checks connected before ops. Reconnect: click Connect again. Production-robust – handles common radio drops in IoT.

Best Practices

  • Filter scans: Use filters: [{services: [UUID]}] or namePrefix for <1% CPU vs passive scan.
  • Negotiate MTU early: getMTU() post-connect maximizes throughput (BLE 5+: 517 bytes).
  • Granular error handling: Distinguish NotSupportedError (no BLE) vs NetworkError (timeout).
  • Persistent permissions: Store device.id in localStorage for reconnection without rescan.
  • Security: Check pairing (device.watchAdvertisements()) and encrypt sensitive payloads.

Common Errors to Avoid

  • Forgot HTTPS: Web Bluetooth blocks HTTP – always vite --https or deploy to Vercel.
  • No disconnect listener: Leads to memory leaks; always addEventListener('gattserverdisconnected').
  • Polling vs Notify: Avoid read() loops (drains battery); prioritize CCCD notifications.
  • UUID case-sensitive: '180f' ≠ '180F' – copy exact hex from device spec.

Next Steps

  • Official docs: Web Bluetooth CG.
  • Expert libs: ble-webjs for abstractions.
  • BLE 5.4: Study Direction Finding and LE Audio.
  • Deploy PWA: Add manifest.json for offline install.
Check our Learni IoT & BLE training courses for hands-on workshops with hardware.