@capacitor-community/bluetooth-le

Bluetooth Low Energy

@capacitor-community/bluetooth-le

Capacitor Bluetooth Low Energy Plugin

Maintainers

Maintainer	GitHub	Social
Patrick Wespi	pwespi

Introduction

This is a Capacitor plugin for Bluetooth Low Energy. It supports the web, Android and iOS.

The goal is to support the same features on all platforms. Therefore the Web Bluetooth API is taken as a guidline for what features to implement.

Below is an index of all the methods available.

• initialize()
• requestDevice(...)
• requestLEScan(...)
• stopLEScan()
• connect(...)
• disconnect(...)
• read(...)
• write(...)
• startNotifications(...)
• stopNotifications(...)
• Interfaces
• Enums

Installation

npm install @capacitor-community/bluetooth-le
npx cap sync

iOS

On iOS, add the NSBluetoothAlwaysUsageDescription to Info.plist, otherwise the app will crash when trying to use Bluetooth (see here).

If the app needs to use Bluetooth while it is in the background, you also have to add bluetooth-central to UIBackgroundModes (for details see here).

./ios/App/App/Info.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>CFBundleDevelopmentRegion</key>
	<string>en</string>
  ...
+	<key>NSBluetoothAlwaysUsageDescription</key>
+	<string>Uses Bluetooth to connect and interact with peripheral BLE devices.</string>
+	<key>UIBackgroundModes</key>
+	<array>
+		<string>bluetooth-central</string>
+	</array>
</dict>
</plist>

Android

On Android, register the plugin in your main activity:

./android/app/src/main/java/<PATH>/MainActivity.java:

+ import com.capacitorjs.community.plugins.bluetoothle.BluetoothLe;

public class MainActivity extends BridgeActivity {

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Initializes the Bridge
    this.init(
        savedInstanceState,
        new ArrayList<Class<? extends Plugin>>() {
          {
            // Additional plugins you've installed go here
            // Ex: add(TotallyAwesomePlugin.class);
+           add(BluetoothLe.class);
          }
        }
      );
  }
}

Configuration

You can configure the strings that are displayed in the device selection dialog on iOS and Android when using requestDevice():

./capacitor.config.json:

{
  "...": "other configuration",
  "plugins": {
    "BluetoothLe": {
      "displayStrings": {
        "scanning": "Am Scannen...",
        "cancel": "Abbrechen",
        "availableDevices": "Verfügbare Geräte",
        "noDeviceFound": "Kein Gerät gefunden"
      }
    }
  }
}

The default values are:

{
  "plugins": {
    "BluetoothLe": {
      "displayStrings": {
        "scanning": "Scanning...",
        "cancel": "Cancel",
        "availableDevices": "Available devices",
        "noDeviceFound": "No device found"
      }
    }
  }
}

Usage

It is recommended to not use the plugin class directly. There is a wrapper class BleClient which makes events and method arguments easier to work with.

// Import the wrapper class directly
import { BleClient } from '@capacitor-community/bluetooth-le';

// DO NOT use this
import { Plugins } from '@capacitor/core';
const { BluetoothLe } = Plugins;

Here is an example of how to use the plugin. It shows how to read the heart rate from a BLE heart rate monitor such as the Polar H10.

import {
  BleClient,
  numbersToDataView,
  numberToUUID,
} from '@capacitor-community/bluetooth-le';

const HEART_RATE_SERVICE = '0000180d-0000-1000-8000-00805f9b34fb';
const HEART_RATE_MEASUREMENT_CHARACTERISTIC =
  '00002a37-0000-1000-8000-00805f9b34fb';
const BODY_SENSOR_LOCATION_CHARACTERISTIC =
  '00002a38-0000-1000-8000-00805f9b34fb';
const BATTERY_SERVICE = numberToUUID(0x180f);
const BATTERY_CHARACTERISTIC = numberToUUID(0x2a19);
const POLAR_PMD_SERVICE = 'fb005c80-02e7-f387-1cad-8acd2d8df0c8';
const POLAR_PMD_CONTROL_POINT = 'fb005c81-02e7-f387-1cad-8acd2d8df0c8';

export async function main() {
  try {
    await BleClient.initialize();

    const device = await BleClient.requestDevice({
      services: [HEART_RATE_SERVICE],
      optionalServices: [BATTERY_SERVICE, POLAR_PMD_SERVICE],
    });

    await BleClient.connect(device.deviceId);
    console.log('connected to device', device);

    const result = await BleClient.read(
      device.deviceId,
      HEART_RATE_SERVICE,
      BODY_SENSOR_LOCATION_CHARACTERISTIC,
    );
    console.log('body sensor location', result.getUint8(0));

    const battery = await BleClient.read(
      device.deviceId,
      BATTERY_SERVICE,
      BATTERY_CHARACTERISTIC,
    );
    console.log('battery level', battery.getUint8(0));

    await BleClient.write(
      device.deviceId,
      POLAR_PMD_SERVICE,
      POLAR_PMD_CONTROL_POINT,
      numbersToDataView([1, 0]),
    );
    console.log('written [1, 0] to control point');

    await BleClient.startNotifications(
      device.deviceId,
      HEART_RATE_SERVICE,
      HEART_RATE_MEASUREMENT_CHARACTERISTIC,
      value => {
        console.log('current heart rate', parseHeartRate(value));
      },
    );

    setTimeout(async () => {
      await BleClient.stopNotifications(
        device.deviceId,
        HEART_RATE_SERVICE,
        HEART_RATE_MEASUREMENT_CHARACTERISTIC,
      );
      await BleClient.disconnect(device.deviceId);
      console.log('disconnected from device', device);
    }, 10000);
  } catch (error) {
    console.error(error);
  }
}

function parseHeartRate(value: DataView): number {
  const flags = value.getUint8(0);
  const rate16Bits = flags & 0x1;
  let heartRate: number;
  if (rate16Bits) {
    heartRate = value.getUint16(1, true);
  } else {
    heartRate = value.getUint8(1);
  }
  return heartRate;
}

An example of using the scanning API:

import { BleClient, numberToUUID } from '@capacitor-community/bluetooth-le';

const HEART_RATE_SERVICE = numberToUUID(0x180d);

export async function scan() {
  try {
    await BleClient.initialize();

    await BleClient.requestLEScan(
      {
        services: [HEART_RATE_SERVICE],
      },
      result => {
        console.log('received new scan result', result);
      },
    );

    setTimeout(async () => {
      await BleClient.stopLEScan();
      console.log('stopped scanning');
    }, 5000);
  } catch (error) {
    console.error(error);
  }
}

API

initialize()

initialize() => Promise<void>

Initialize Bluetooth Low Energy (BLE). If it fails, BLE might be unavailable or disabled on this device. On Android it will ask for the location permission. On iOS it will ask for the Bluetooth permission. For an example, see usage.

---

requestDevice(...)

requestDevice(options?: RequestBleDeviceOptions | undefined) => Promise<BleDevice>

Request a peripheral BLE device to interact with. This will scan for available devices according to the filters in the options and show a dialog to pick a device. For an example, see usage.

Param	Type	Description
options	RequestBleDeviceOptions	Device filters, see RequestBleDeviceOptions

Returns: Promise<BleDevice>

---

requestLEScan(...)

requestLEScan(options: RequestBleDeviceOptions, callback: (result: ScanResult) => void) => Promise<void>

Start scanning for BLE devices to interact with according to the filters in the options. The callback will be invoked on each device that is found. Scanning will continue until stopLEScan is called. For an example, see usage. NOTE: Use with care on web platform, the required API is still behind a flag in most browsers.

Param	Type
options	RequestBleDeviceOptions
callback	(result: ScanResult) => void

---

stopLEScan()

stopLEScan() => Promise<void>

Stop scanning for BLE devices. For an example, see usage.

---

connect(...)

connect(deviceId: string) => Promise<void>

Connect to a peripheral BLE device. For an example, see usage.

Param	Type	Description
deviceId	string	The ID of the device to use (obtained from requestDevice or requestLEScan)

---

disconnect(...)

disconnect(deviceId: string) => Promise<void>

Disconnect from a peripheral BLE device. For an example, see usage.

Param	Type	Description
deviceId	string	The ID of the device to use (obtained from requestDevice or requestLEScan)

---

read(...)

read(deviceId: string, service: string, characteristic: string) => Promise<DataView>

Read the value of a characteristic. For an example, see usage.

Param	Type	Description
deviceId	string	The ID of the device to use (obtained from requestDevice or requestLEScan)
service	string	UUID of the service (see UUID format)
characteristic	string	UUID of the characteristic (see UUID format)

Returns: Promise<DataView>

---

write(...)

write(deviceId: string, service: string, characteristic: string, value: DataView) => Promise<void>

Write a value to a characteristic. For an example, see usage.

Param	Type	Description
deviceId	string	The ID of the device to use (obtained from requestDevice or requestLEScan)
service	string	UUID of the service (see UUID format)
characteristic	string	UUID of the characteristic (see UUID format)
value	DataView	The value to write as a DataView. To create a DataView from an array of numbers, there is a helper function, e.g. numbersToDataView([1, 0])

---

startNotifications(...)

startNotifications(deviceId: string, service: string, characteristic: string, callback: (value: DataView) => void) => Promise<void>

Start listening to changes of the value of a characteristic. For an example, see usage.

Param	Type	Description
deviceId	string	The ID of the device to use (obtained from requestDevice or requestLEScan)
service	string	UUID of the service (see UUID format)
characteristic	string	UUID of the characteristic (see UUID format)
callback	(value: DataView) => void	Callback function to use when the value of the characteristic changes

---

stopNotifications(...)

stopNotifications(deviceId: string, service: string, characteristic: string) => Promise<void>

Stop listening to the changes of the value of a characteristic. For an example, see usage.

Param	Type	Description
deviceId	string	The ID of the device to use (obtained from requestDevice or requestLEScan)
service	string	UUID of the service (see UUID format)
characteristic	string	UUID of the characteristic (see UUID format)

---

Interfaces

BleDevice

Prop	Type	Description
deviceId	string	ID of the device, which will be needed for further calls. On Android this is the BLE MAC address. On iOS and web it is an identifier.
name	string	Name of the device.
uuids	string[]

RequestBleDeviceOptions

Prop	Type	Description
services	string[]	Filter devices by service UUIDs. UUIDs have to be specified as 128 bit UUID strings in lowercase, e.g. ['0000180d-0000-1000-8000-00805f9b34fb'] There is a helper function to convert numbers to UUIDs. e.g. [numberToUUID(0x180f)]. (see UUID format)
name	string	Filter devices by name
namePrefix	string	Filter devices by name prefix
optionalServices	string[]	For web, all services that will be used have to be listed under services or optionalServices, e.g. [numberToUUID(0x180f)] (see UUID format)
allowDuplicates	boolean	Normally scans will discard the second and subsequent advertisements from a single device. If you need to receive them, set allowDuplicates to true (only applicable in requestLEScan). (default: false)
scanMode	ScanMode	Android scan mode (default: ScanMode.SCAN_MODE_BALANCED)

ScanResult

Prop	Type	Description
device	BleDevice	The device that was found in the scan
rssi	number	Received Signal Strength Indication
txPower	number	Transmit power in dBm. A value of 127 indicates that it is not available.
manufacturerData	{ [key: string]: DataView; }	Manufacturer data, key is a company identifier and value is the data
serviceData	{ [key: string]: DataView; }	Service data, key is a service UUID and value is the data
uuids	string[]	Advertised services
rawAdvertisement	DataView	Raw advertisement data (Android only)

DataView

Prop	Type
buffer	ArrayBuffer
byteLength	number
byteOffset	number

Method	Signature	Description
getFloat32	(byteOffset: number, littleEndian?: boolean | undefined) => number	Gets the Float32 value at the specified byte offset from the start of the view. There is no alignment constraint; multi-byte values may be fetched from any offset.
getFloat64	(byteOffset: number, littleEndian?: boolean | undefined) => number	Gets the Float64 value at the specified byte offset from the start of the view. There is no alignment constraint; multi-byte values may be fetched from any offset.
getInt8	(byteOffset: number) => number	Gets the Int8 value at the specified byte offset from the start of the view. There is no alignment constraint; multi-byte values may be fetched from any offset.
getInt16	(byteOffset: number, littleEndian?: boolean | undefined) => number	Gets the Int16 value at the specified byte offset from the start of the view. There is no alignment constraint; multi-byte values may be fetched from any offset.
getInt32	(byteOffset: number, littleEndian?: boolean | undefined) => number	Gets the Int32 value at the specified byte offset from the start of the view. There is no alignment constraint; multi-byte values may be fetched from any offset.
getUint8	(byteOffset: number) => number	Gets the Uint8 value at the specified byte offset from the start of the view. There is no alignment constraint; multi-byte values may be fetched from any offset.
getUint16	(byteOffset: number, littleEndian?: boolean | undefined) => number	Gets the Uint16 value at the specified byte offset from the start of the view. There is no alignment constraint; multi-byte values may be fetched from any offset.
getUint32	(byteOffset: number, littleEndian?: boolean | undefined) => number	Gets the Uint32 value at the specified byte offset from the start of the view. There is no alignment constraint; multi-byte values may be fetched from any offset.
setFloat32	(byteOffset: number, value: number, littleEndian?: boolean | undefined) => void	Stores an Float32 value at the specified byte offset from the start of the view.
setFloat64	(byteOffset: number, value: number, littleEndian?: boolean | undefined) => void	Stores an Float64 value at the specified byte offset from the start of the view.
setInt8	(byteOffset: number, value: number) => void	Stores an Int8 value at the specified byte offset from the start of the view.
setInt16	(byteOffset: number, value: number, littleEndian?: boolean | undefined) => void	Stores an Int16 value at the specified byte offset from the start of the view.
setInt32	(byteOffset: number, value: number, littleEndian?: boolean | undefined) => void	Stores an Int32 value at the specified byte offset from the start of the view.
setUint8	(byteOffset: number, value: number) => void	Stores an Uint8 value at the specified byte offset from the start of the view.
setUint16	(byteOffset: number, value: number, littleEndian?: boolean | undefined) => void	Stores an Uint16 value at the specified byte offset from the start of the view.
setUint32	(byteOffset: number, value: number, littleEndian?: boolean | undefined) => void	Stores an Uint32 value at the specified byte offset from the start of the view.

ArrayBuffer

Represents a raw buffer of binary data, which is used to store data for the different typed arrays. ArrayBuffers cannot be read from or written to directly, but can be passed to a typed array or DataView Object to interpret the raw buffer as needed.

Prop	Type	Description
byteLength	number	Read-only. The length of the ArrayBuffer (in bytes).

Method	Signature	Description
slice	(begin: number, end?: number | undefined) => ArrayBuffer	Returns a section of an ArrayBuffer.

Enums

ScanMode

Members	Value	Description
SCAN_MODE_LOW_POWER	0	Perform Bluetooth LE scan in low power mode. This mode is enforced if the scanning application is not in foreground. https://developer.android.com/reference/android/bluetooth/le/ScanSettings#SCAN_MODE_LOW_POWER
SCAN_MODE_BALANCED	1	Perform Bluetooth LE scan in balanced power mode. (default) Scan results are returned at a rate that provides a good trade-off between scan frequency and power consumption. https://developer.android.com/reference/android/bluetooth/le/ScanSettings#SCAN_MODE_BALANCED
SCAN_MODE_LOW_LATENCY	2	Scan using highest duty cycle. It's recommended to only use this mode when the application is running in the foreground. https://developer.android.com/reference/android/bluetooth/le/ScanSettings#SCAN_MODE_LOW_LATENCY

UUID format

All UUIDs have to be provided in 128 bit format as string (lowercase), e.g. '0000180d-0000-1000-8000-00805f9b34fb'. There is a helper function to convert 16 bit UUID numbers to string:

import { numberToUUID } from '@capacitor-community/bluetooth-le';

const HEART_RATE_SERVICE = numberToUUID(0x180d);
// '0000180d-0000-1000-8000-00805f9b34fb'

Changelog

0.1.0 (2020-12-28)

• add requestLEScan
• add stopLEScan
• add Android scan mode
• add namePrefix filter
• fix getting some events twice
• fix invalid deviceId on Android
• fix device initialization on iOS