Heartbeat Scanner

Using Bluetooth Low Energy (BLE) library to read Polar Verity sensor

Bluetooth Low Energy (BLE) library Setup

npm install node-ble

Provide permissions

In order to allow a connection with the DBus daemon, you have to set up right permissions.

Create the file /etc/dbus-1/system.d/node-ble.conf with the following content (customize with userid)

<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
  "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
  <policy user="%userid%">
   <allow own="org.bluez"/>
    <allow send_destination="org.bluez"/>
    <allow send_interface="org.bluez.GattCharacteristic1"/>
    <allow send_interface="org.bluez.GattDescriptor1"/>
    <allow send_interface="org.freedesktop.DBus.ObjectManager"/>
    <allow send_interface="org.freedesktop.DBus.Properties"/>
  </policy>
</busconfig>

STEP 1: Get Adapter

To start a Bluetooth Low Energy (BLE) connection you need a Bluetooth adapter.

const {createBluetooth} = require('node-ble')
const {bluetooth, destroy} = createBluetooth()
const adapter = await bluetooth.defaultAdapter()

STEP 2: Start discovering

In order to find a Bluetooth Low Energy device out, you have to start a discovery operation.

if (! await adapter.isDiscovering())
  await adapter.startDiscovery()

STEP 3: Get a device, Connect and Get GATT Server

Use an adapter to get a remote Bluetooth device, then connect to it and bind to the GATT (Generic Attribute Profile) server.

const device = await adapter.waitDevice('00:00:00:00:00:00')
await device.connect()
const gattServer = await device.gatt()

STEP 4a: Read and write a characteristic

const service1 = await gattServer.getPrimaryService('uuid')
const characteristic1 = await service1.getCharacteristic('uuid')
await characteristic1.writeValue(Buffer.from("Hello world"))
const buffer = await characteristic1.readValue()
console.log(buffer)

STEP 4b: Subscribe to a characteristic

const service2 = await gattServer.getPrimaryService('uuid')
const characteristic2 = await service2.getCharacteristic('uuid')
await characteristic2.startNotifications()
characteristic2.on('valuechanged', buffer => {
  console.log(buffer)
})
await characteristic2.stopNotifications()

STEP 5: Disconnect

When you have done you can disconnect and destroy the session.

await device.disconnect()
destroy()

Reference

const {createBluetooth} = require('node-ble')
const {bluetooth, destroy} = createBluetooth()

Method	Description
Bluetooth bluetooth
void destroy()

Bluetooth

Method	Description
Promise<String[]> adapters()	List of available adapters
Promise<Adapter> defaultAdapter()	Get an available adapter
Promise<Adapter> getAdapter(String adapter)	Get a specific adapter (one of available in adapters())

Adapter

Method	Description
Promise<String> getAddress()	The Bluetooth device address.
Promise<String> getAddressType()	The Bluetooth Address Type. One of public or random.
Promise<String> getName()	The Bluetooth system name (pretty hostname).
Promise<String> getAlias()	The Bluetooth friendly name.
Promise<bool> isPowered()	Adapter power status.
Promise<bool> isDiscovering()	Indicates that a device discovery procedure is active.
Promise<void> startDiscovery()	Starts the device discovery session.
Promise<void> stopDiscovery()	Cancel any previous StartDiscovery transaction.
Promise<String[]> devices()	List of discovered Bluetooth Low Energy devices
Promise<Device> getDevice(String uuid)	Returns an available Bluetooth Low Energy (waitDevice is preferred)
Promise<Device> waitDevice(String uuid)	Returns a Bluetooth Low Energy device as soon as it is available
Promise<String> toString()	User friendly adapter name

Device extends EventEmitter

Method	Description
Promise<String> getName()	The Bluetooth remote name.
Promise<String> getAddress()	The Bluetooth device address of the remote device.
Promise<String> getAddressType()	The Bluetooth Address Type. One of public or random.
Promise<String> getAlias()	The name alias for the remote device.
Promise<String> getRSSI()	Received Signal Strength Indicator of the remote device.
Promise<String> isPaired()	Indicates if the remote device is paired.
Promise<String> isConnected()	Indicates if the remote device is currently connected.
Promise<void> pair()	Connects to the remote device, initiate pairing and then retrieve GATT primary services (needs a default agent to handle wizard).
Promise<void> cancelPair()	This method can be used to cancel a pairing operation initiated by the Pair method.
Promise<void> connect()	This is a generic method to connect any profiles the remote device supports that can be connected to and have been flagged as auto-connectable on our side.
Promise<void> disconnect()	This method gracefully disconnects all connected profiles and then terminates low-level ACL connection.
Promise<GattServer> gatt()	Waits services resolving, then returns a connection to the remote Gatt Server
Promise<String> toString()	User friendly device name.

Event	Description
connect	Connected to device
disconnect	Disconnected from device

GattServer

Method	Description
Promise<String[]> services()	List of available services
Promise<GattService> getPrimaryService(String uuid)	Returns a specific Primary Service

GattService

Method	Description
Promise<bool> isPrimary()	Indicates whether or not this GATT service is a primary service.
Promise<String> getUUID()	128-bit service UUID.
Promise<String[]> characteristics()	List of available characteristic UUIDs.
Promise<GattCharacteristic> getCharacteristic(String uuid)	Returns a specific characteristic.
Promise<String> toString()	User friendly service name.

GattCharacteristic extends EventEmitter

Method	Description
Promise<String> getUUID()	128-bit characteristic UUID.
Promise<String[]> getFlags()	Defines how the characteristic value can be used.
Promise<bool> isNotifying()	True, if notifications or indications on this characteristic are currently enabled.
Promise<Buffer> readValue(Number offset = 0)	Issues a request to read the value of the characteristic and returns the value if the operation was successful.
Promise<void> writeValue(Buffer buffer, WriteValueOptions options = {})	Issues a request to write the value of the characteristic. Default options { offset: 0, type: 'reliable' }.
Promise<void> startNotifications()	Starts a notification session from this characteristic if it supports value notifications or indications.
Promise<void> stopNotifications()	This method will cancel any previous StartNotify transaction.
Promise<String> toString()	User friendly characteristic name.

Event	Description
valuechanged	New value is notified. (invoke startNotifications() to enable notifications)

Compatibility

This library works on many architectures supported by Linux. It leverages on Bluez driver, a component supported by the following platforms and distributions https://www.bluez.org/about

Node-ble has been tested on the following environment:

• Raspbian GNU/Linux 10 (buster)
• Ubuntu 18.04.4 LTS
• Ubuntu 20.04 LTS

Changelog

• 0.x - Beta version
• 1.0 - First official version
• 1.1 - Migrates to gh-workflows
• 1.2 - Upgrades deps
• 1.3 - Adds typescript definitions #10
• 1.4 - Upgrades deps
• 1.5 - Adds write options configuration async writeValue (value, optionsOrOffset = {}) #20; Upgrades deps
• 1.6 - Upgrades deps and removes some dependencies; migrates to npm; improves gh-actions

Contributors

• chrvadala (author)
• pascalopitz
• lupol

Run tests

In order to run test suite you have to set up right DBus permissions.

Create the file /etc/dbus-1/system.d/node-ble-test.conf with the following content (customize with userid)

<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
  "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
  <policy user="%userid%">
    <allow own="org.test"/>
    <allow send_destination="org.test"/>
    <allow send_interface="org.test.iface"/>
  </policy>
</busconfig>

Unit tests

npm test

End to end (e2e) tests

The end to end test will try to connect to a real bluetooth device and read some characteristics. To do that, you need two different devices.

Device 1

wget https://git.kernel.org/pub/scm/bluetooth/bluez.git/plain/test/example-advertisement
wget https://git.kernel.org/pub/scm/bluetooth/bluez.git/plain/test/example-gatt-server
python example-advertisement
python example-gatt-server
hcitool dev #this command shows bluetooth address

Device 2

TEST_DEVICE=00:00:00:00:00:00 npm run test:e2e

References

• https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc/adapter-api.txt
• https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc/device-api.txt
• https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc/gatt-api.txt
• https://webbluetoothcg.github.io/web-bluetooth - method signatures follow, when possible, WebBluetooth standards
• https://developers.google.com/web/updates/2015/07/interact-with-ble-devices-on-the-web - method signatures follow, when possible, WebBluetooth standards

Similar libraries

• https://github.com/noble/noble
• https://github.com/abandonware/noble (noble fork)
• https://www.npmjs.com/package/node-web-bluetooth

Useful commands

Command	Description
rm -r /var/lib/bluetooth/*	Clean Bluetooth cache
hciconfig -a	Adapter info
hcitool dev	Adapter info (through Bluez)
d-feet	DBus debugging tool
nvram bluetoothHostControllerSwitchBehavior=never	Only on Parallels