Web Bluetooth Control Guide

// Request connection to a LEGO hub
const device = await navigator.bluetooth.requestDevice({
  filters: [
    { namePrefix: 'LEGO' },
    { services: ['00001623-1212-efde-1623-785feabcd123'] }
  ],
  optionalServices: ['00001623-1212-efde-1623-785feabcd123']
});

console.log('Connected to:', device.name);

// Connect to GATT server
const server = await device.gatt.connect();

// Get the LEGO Hub service
const service = await server.getPrimaryService(
  '00001623-1212-efde-1623-785feabcd123'
);

// Get the characteristic for sending commands
const characteristic = await service.getCharacteristic(
  '00001624-1212-efde-1623-785feabcd123'
);

// Command to start motor on port A at 50% speed
// Format: [length, hub_id, message_type, port, start_speed, max_power, end_state, profile]
const command = new Uint8Array([
  0x08,  // Message length
  0x00,  // Hub ID
  0x81,  // Port output command
  0x00,  // Port A
  0x11,  // Start speed subcommand
  0x32,  // Speed: 50 (0x32 = 50)
  0x64,  // Max power: 100
  0x00   // Use profile 0
]);

await characteristic.writeValue(command);

// Enable notifications
await characteristic.startNotifications();

// Listen for incoming data
characteristic.addEventListener('characteristicvaluechanged', (event) => {
  const data = new Uint8Array(event.target.value.buffer);
  console.log('Received:', Array.from(data).map(b => b.toString(16)));

  // Parse sensor data based on message type
  const messageType = data[2];
  if (messageType === 0x45) {  // Sensor value message
    const port = data[3];
    const value = data[4];
    console.log(`Port ${port} sensor value: ${value}`);
  }
});