NodeJS BLE Applications using BLENO on Arch Linux

BLENO is a greate NodeJS based library for building applications that communicat with other devices (Smartphones, tables, sensor tags) using Bluetooth Low Energy (BLE).

This post is just to quickly document some requirements for successfully use the BLENO library, in my case, on Arch Linux running the latest Plasma (KDE) desktop.

The tools:

Most the information available on the internet for using and controlling the bluetooth adapter uses the now deprecated tools hcitool, hciconfig and so on. Check here the deprecated list of commands.

So we need to use the new tools from the latest Bluez (Bluetooth Linux implementation): btmgm, btinfo, …

Making Bleno examples work:

The simplest example to try out the BLENO library is the battery example located at: […]/bleno/examples/battery-service

First let’s check if our computer/laptop bluetooth adapter is available: Note that all commands must be ran as the root user:

root@pcortex:/opt/bleno/examples/battery-service# btinfo local
Bluetooth information utility ver 5.45
Failed to open HCI user channel
root@pcortex:/opt/bleno/examples/battery-service# 

This issue can be circumvented by stopping the higher level bluetooth stack:

root@pcortex:/opt/bleno/examples/battery-service# systemctl stop bluetooth
root@pcortex:/opt/bleno/examples/battery-service# btinfo local
Bluetooth information utility ver 5.45
HCI version: 6
HCI revision: 7869
LMP version: 6
LMP subversion: 64512
Manufacturer: 2
root@pcortex:/opt/bleno/examples/battery-service#

In case of previously disabling the Bluetooth through the graphical interface:

Disabling the Bluetooth here will have this behaviour (in this case the bluetooth service is still running):

root@pcortex:/opt/bleno/examples/battery-service# systemctl start bluetooth   (<- After this disable bluetooth on the graphical interface)
root@pcortex:/opt/bleno/examples/battery-service# btinfo local
Bluetooth information utility ver 5.45
Failed to open HCI user channel
root@pcortex:/opt/bleno/examples/battery-service# btmgmt power on
Set Powered for hci0 failed with status 0x12 (Blocked through rfkill)
root@pcortex:/opt/bleno/examples/battery-service# 

Even stopping the Bluetooth service keeps the BT adapter disabled:

root@pcortex:/opt/bleno/examples/battery-service# systemctl stop bluetooth
root@pcortex:/opt/bleno/examples/battery-service# btmgmt power on
Set Powered for hci0 failed with status 0x12 (Blocked through rfkill)
root@pcortex:/opt/bleno/examples/battery-service#

We can check this with the rfkill command:

root@pcortex:/opt/bleno/examples/battery-service# rfkill list
0: phy0: Wireless LAN
        Soft blocked: no
        Hard blocked: no
2: hci0: Bluetooth
        Soft blocked: yes
        Hard blocked: no
root@pcortex:/opt/bleno/examples/battery-service# 

We can unblock now the adapter:

root@pcortex:/opt/bleno/examples/battery-service# rfkill unblock 2
root@pcortex:/opt/bleno/examples/battery-service# rfkill list
0: phy0: Wireless LAN
        Soft blocked: no
        Hard blocked: no
2: hci0: Bluetooth
        Soft blocked: no
        Hard blocked: no
root@pcortex:/opt/bleno/examples/battery-service# btinfo local
Bluetooth information utility ver 5.45
HCI version: 6
HCI revision: 7869
LMP version: 6
LMP subversion: 64512
Manufacturer: 2
root@pcortex:/opt/bleno/examples/battery-service# btmgmt power on
hci0 class of device changed: 0x00010c
hci0 Set Powered complete, settings: powered bondable ssp br/edr le secure-conn 
root@pcortex:/opt/bleno/examples/battery-service# 

So why we are having all this work for making sure that the BT adapter is powered on AND the bluetooth stack is stopped (systemctl stop bluetooth).

The answer is quite simple. If we don’t do this the BLENO examples will seem to work (they start) but the BLE advertised services are the bluetooth Bluez services and not our code.

To explain, check the following behaviour where we start the BLENO Battery Service with the Bluetooth stack started:

root@halcyon:/opt/bleno/examples/battery-service# systemctl start bluetooth
root@halcyon:/opt/bleno/examples/battery-service# node main.js 
on -> stateChange: poweredOn
on -> advertisingStart: success
setServices: success

Using the Nordic nRF Connect Android App we can see the non working behaviour vs what we should expect from the Bleno Battery example:

BLE Scan Results

Pressing Connect we can see on Client that no service are provided. This is due to the fact that the desktop bluetooth is enabled):

Now let’s disable the bluetooth stack (which powers the BT adapter) and start again the Bleno Battery example:

root@pcortex:/opt/bleno/examples/battery-service# systemctl stop bluetooth
root@pcortex:/opt/bleno/examples/battery-service# node main.js 

Example hangs in here, because BT adapter is disabled/off

^Croot@pcortex:/opt/bleno/examples/battery-service# btmgmt power on
hci0 class of device changed: 0x00010c
hci0 Set Powered complete, settings: powered bondable ssp br/edr le secure-conn 
root@pcortex:/opt/bleno/examples/battery-service# node main.js 
on -> stateChange: poweredOn
on -> advertisingStart: success
setServices: success

And now if we scan again and connect to the Battery example with our mobile phone through the Nordic application we have:

It works now!

We can confirm that because on the file battery-service.js the service identifier is defined:

function BatteryService() {
  BatteryService.super_.call(this, {
      //uuid: '180F',
      uuid: 'ff51b30e-d7e2-4d93-8842-a7c4a57dfb07',
      characteristics: [
          new BatteryLevelCharacteristic()
      ]
  });
}

and it is the same detected by the Android application.