Ubuntu – How to show battery percentage of a Bluetooth connected gadget (headphone)

Bluetooth daemon

In the default installation a daemon (bluetoothd) runs in the background (run from the file /etc/init.d/bluetooth). This daemon takes care on recognizing and connecting to known bluetooth devices and may be cofigured with configuration files in /etc/bluetooth. For autoconneting a headset the following line in audio.conf should be uncommented (remove #):

AutoConnect=true

To restart the daemon type sudo /etc/init.d/bluetooth restart.

_{Remark: Using the command line tool sudo hcitool cc <MAC-Adress> did not lead to a stable connection to a known device in the test environment here when the daemon was running.}

DBus

In order to connect a disconnected but physically present and paired headset we can use D-Bus from a script. Here's an example in python:

#!/usr/bin/python
# Toggles headset connection

import dbus
from dbus.mainloop.glib import DBusGMainLoop

dbus_loop = DBusGMainLoop()
bus = dbus.SystemBus(mainloop=dbus_loop)

#Get dbus interface for headset
manager = bus.get_object('org.bluez', '/')
iface_m = dbus.Interface(manager, 'org.bluez.Manager')
adapterPath = iface_m.DefaultAdapter()
adapter = bus.get_object('org.bluez', adapterPath)
iface_a = dbus.Interface(adapter, 'org.bluez.Adapter')
devicePath = iface_a.ListDevices()[0]  # assuming first device
device = bus.get_object('org.bluez', devicePath)
iface_h = dbus.Interface(device, 'org.bluez.Headset')

#Check state of connection
connected = iface_h.IsConnected()
print 'Toggling connection. Please wait'
# toggle connection
if not connected:
    try:
        iface_h.Connect()
        print 'Connecting: ', devicePath
    except:
        print 'Device not found'
else:
    iface_h.Disconnect()
    print 'Disconnecting: ', devicePath

In case we have more than one Bluetooth device we will have to adapt the devicePath appropriately, of course. The example above will connect a Headset. Change the interface to a different protocol for any other service (e.g. AudioSink).

Pulseaudio

If you know the MAC adress of your Bluetooth device you can connect it as an output sink for pulseaudio by:

pacmd set-default-sink bluez_sink.xx_xx_xx_xx_xx_xx

Where xx_xx_xx_xx_xx_xx is the MAC address (replace ':' by '_' for pulseaudio to recognize it).

See also this answer for more details.

It looks like the underlying problem was similar to the one for this question:

https://stackoverflow.com/questions/31380594/linux-bluez-dbus-communication

Except that I'm running a systemd linux setup so I had to do as the comment on that answer suggested:

With newer Systemd-based systems, copy /lib/systemd/system/bluetooth.service to /etc/systemd/system/bluetooth.service and change the ExecStart line to ExecStart=/usr/lib/bluetooth/bluetoothd -E.

– Arto Bendiken

So I did that, restarted, and then started bluetoothctl, and connected manually:

[Bose QuietComfort 35]# connect 04:52:C7:32:68:16 
Attempting to connect to 04:52:C7:32:68:16
[CHG] Device 04:52:C7:32:68:16 Paired: yes
Connection successful

This time when I paired, my headphones recognised the connection (they didn't previously, even though GNOME seemed to think the pairing had worked) and the output device appeared in my devices list.