@abandonware/noble/examples/echo.js

A Node.js BLE (Bluetooth Low Energy) central library.

/* eslint-disable handle-callback-err */
// Connect to a peripheral running the echo service
// https://github.com/noble/bleno/blob/master/examples/echo

// subscribe to be notified when the value changes
// start an interval to write data to the characteristic

// const noble = require('noble');
const noble = require('..');

const ECHO_SERVICE_UUID = 'ec00';
const ECHO_CHARACTERISTIC_UUID = 'ec0e';

noble.on('stateChange', (state) => {
  if (state === 'poweredOn') {
    console.log('Scanning');
    noble.startScanning([ECHO_SERVICE_UUID], false);
  } else {
    noble.stopScanning();
  }
});

noble.on('discover', (peripheral) => {
  // connect to the first peripheral that is scanned
  noble.stopScanning();
  const name = peripheral.advertisement.localName;
  console.log(`Connecting to '${name}' ${peripheral.id}`);
  connectAndSetUp(peripheral);
});

function connectAndSetUp (peripheral) {
  peripheral.connect((error) => {
    if (error) {
      console.error(error);
      return;
    }

    console.log('Connected to', peripheral.id);

    // specify the services and characteristics to discover
    const serviceUUIDs = [ECHO_SERVICE_UUID];
    const characteristicUUIDs = [ECHO_CHARACTERISTIC_UUID];

    peripheral.discoverSomeServicesAndCharacteristics(
      serviceUUIDs,
      characteristicUUIDs,
      onServicesAndCharacteristicsDiscovered
    );
  });

  peripheral.on('disconnect', () => console.log('disconnected'));
}

function onServicesAndCharacteristicsDiscovered (
  error,
  services,
  characteristics
) {
  if (error) {
    console.error(error);
    return;
  }

  console.log('Discovered services and characteristics');
  const echoCharacteristic = characteristics[0];

  // data callback receives notifications
  echoCharacteristic.on('data', (data, isNotification) => {
    console.log(`Received: "${data}"`);
  });

  // subscribe to be notified whenever the peripheral update the characteristic
  echoCharacteristic.subscribe((error) => {
    if (error) {
      console.error('Error subscribing to echoCharacteristic');
    } else {
      console.log('Subscribed for echoCharacteristic notifications');
    }
  });

  // create an interval to send data to the service
  let count = 0;
  setInterval(() => {
    count++;
    const message = Buffer.from(`hello, ble ${count}`, 'utf-8');
    console.log(`Sending:  '${message}'`);
    echoCharacteristic.write(message);
  }, 2500);
}

process.on('SIGINT', function () {
  console.log('Caught interrupt signal');
  noble.stopScanning(() => process.exit());
});

process.on('SIGQUIT', function () {
  console.log('Caught interrupt signal');
  noble.stopScanning(() => process.exit());
});

process.on('SIGTERM', function () {
  console.log('Caught interrupt signal');
  noble.stopScanning(() => process.exit());
});