Raspberry Pi Bluetooth Speaker

2023-02-04T13:27:53Z

Gomgom: Add hint to packages bluez-alsa-utils bluez-alsa-openrc

=How To Build a Raspberry Pi Bluetooth Speaker=

This articles describes how to build a Bluetooth speaker. This article is being actively written. Currently it is full of bugs but will provide some useful pointers.

=Before You Start=
You’ll need:
* A Raspberry Pi
* A Bluetooth USB dongle (if your Pi doesn’t have Bluetooth on board)
* Sound card and speaker(s)

=Article Completion=
# Test everything
# Turn every background task into a service
# More investigation on Bluetooth pairing

=Getting the Speaker(s) Working=
To get the best results, you'll need an dedicated audio add-on board and matching speakers. Higher end passive speakers need a proper amplifier (e.g. HiFiBerry Amp2 or IQaudIO IQaudIO DigiAMP+).

I've used the whole range of IQaudio audio boards with different speakers and headphones. I'd also recommend a dedicated USB Bluetooth dongle (don't get the cheapest versions of these). It is possible to test by using the on-board Bluetooth and the on-board audio with headphones but because of dropped packets, the audio quality isn't great.

Once the speakers and audio card are connected to the Raspberry Pi, it's time to install a fresh version of Alpine Linux. The armv7 version from the [https://alpinelinux.org/downloads/ Downloads] page works on almost all Pis. This Wiki has several articles about installing Alpine on a Raspberry Pi.

Enable writing to the boot media:

mount /media/mmcblk0p1 -o rw,remount

Then, either enable the on board sound:

echo "dtparam=audio=on" >> /media/mmcblk0p1/usercfg.txt

or your sound card (e.g. IQaudIO):

echo "dtoverlay=iqaudio-dacplus,unmute_amp" >> /media/mmcblk0p1/usercfg.txt

reboot.

Follow [https://wiki.alpinelinux.org/wiki/ALSA these instructions] to enable ALSA. In summary

apk add alsa-utils alsa-utils-doc alsa-lib alsaconf # the required software for sound
aplay -l # should display a List of PLAYBACK Hardware Devices

In my case my list is:

**** List of PLAYBACK Hardware Devices ****
card 0: Headphones [bcm2835 Headphones], device 0: bcm2835 Headphones [bcm2835 Headphones]
Subdevices: 8/8
Subdevice #0: subdevice #0
Subdevice #1: subdevice #1
Subdevice #2: subdevice #2
Subdevice #3: subdevice #3
Subdevice #4: subdevice #4
Subdevice #5: subdevice #5
Subdevice #6: subdevice #6

Before you play anything from your speakers, I recommend turnong down the volume.

amixer

displays a list of "simple controls." For my headphones and the on-board sound, the output looks like this:

Simple mixer control 'Headphone',0
Capabilities: pvolume pvolume-joined pswitch pswitch-joined
Playback channels: Mono
Limits: Playback -10239 - 400
Mono: Playback 0 [96%] [0.00dB] [on]

In this case, there is only 1 control, 'Headphone', so I issue this command to lower the maximum volume to a comfortable level. (50%)

amixer sset Headphone 50%

The IQaudIO DAC that I use has a much larger set of controls. I issued this command to set the volume:

amixer sset 'Digital' 50 # quotes may be required if there are spaces in the control name

Note: there can be several interlinked controls, some of which are muted by defualt. ALSA (and other audio software on Linux) is notoriously under-documented, try `man amixer` for more information. Sometimes it is easier to use a more visual control to change the configuration:

alsamixer

Finally, if you issue this command:

speaker-test -t wav -c 2

Then you should hear "Front Left, Front Right" repeating from your chosen speakers. Now it's time to setup Bluetooth. Don't forget to save your changes (lbu commit).

=Bluetooth=
I used [https://wiki.alpinelinux.org/wiki/Raspberry_Pi_3_-_Setting_Up_Bluetooth Raspberry Pi 3 - Setting Up Bluetooth] as a reference with some slight modifications as I am using a Pi 4.

Raspberry Pi 4

apk add bluez
btattach -B /dev/ttyAMA0 -P bcm -S 3000000 &
# btattach -B /dev/ttyAMA0 -P bcm -S 115200 -N & # Pi 3 - not tested by me
rc-service bluetooth start

edit {{Path|/etc/mdev.conf}} and enable bluetooth. We're using `sed`, where '''s/#rpi bluetooth/rpi bluetooth/''' means replace '''#rpi bluetooth''' with '''rpi bluetooth'''.

sed -i 's/#rpi bluetooth/rpi bluetooth/' /etc/mdev.conf
sed -i 's/#ttyAMA0 root:tty 660 @btattach -B \/dev\/$MDEV -P bcm -S 115200/ttyAMA0 root:tty 660 @btattach -B \/dev\/$MDEV -P bcm -S 3000000/' /etc/mdev.conf

Note: the last command uncomments the ''btattach'' command and changes it to work with the Pi 4.

Changes to {{Path|/etc/bluetooth/main.conf}}

Name = Pi-Bluetooth-Speaker # This is what you'll see when connecting
Class = 0x41C # Adding audio playback and recording to this Bluetooth device
DiscoverableTimeout = 0 # Always discoverable
AlwaysPairable = true # Always pairable
PairableTimeout = 0 # no time limit
AutoEnable=true # starts Bluetooth when Linux 'sees' the Bluetooth device at boot

Ensure that Bluetooth is started at boot:

rc-update add bluetooth

Bluetooth's state, including paired devices, in held in {{Path|/var/lib/bluetooth}} so you'll need to add this to `lbu` state:

lbu include /var/lib/bluetooth
lbu commit && reboot

Manual device pairing

bluetoothctl

[bluetooth]# discoverable on
[agent] Confirm passkey 627133 (yes/no): yes
[agent] Authorize service 0000110e-0000-1000-8000-00805f9b34fb (yes/no): yes

Device pairing:

apk add python3 py3-dbus py3-gobject3

Getting this to work currently involves running the bluez-simple-agent after having edited it to always return sucessful. You'll need to comment out some lines (by adding "#" at the beginning):

vi /usr/bin/bluez-simple-agent

#import bluezutils

def RequestConfirmation(self, device, passkey):
#print("RequestConfirmation (%s, %06d)" % (device, passkey))
#confirm = ask("Confirm passkey (yes/no): ")
#if (confirm == "yes"):
set_trusted(device)
return
#raise Rejected("Passkey doesn't match")

And then running the revised agent in the background, and pair your devices:

bluez-simple-agent &
lbu include /usr/bin/bluez-simple-agent
lbu commit

Notes: [https://www.kynetics.com/docs/2018/pairing_agents_bluez/ Pairing Agents in BlueZ stack]
[https://stackoverflow.com/questions/59214524/since-bluez-5-48-iphones-require-pairing-when-connecting-on-a-ble-gap-periphera Since Bluez 5.48, iPhones require pairing when connecting on a BLE GAP peripheral, why?]
[https://gist.github.com/mill1000/74c7473ee3b4a5b13f6325e9994ff84c Headless A2DP Audio Streaming on Raspbian Stretch ]

=bluez-alsa=
At the time of writing this article, bluez-alsa is only found in the community repositories, so you need to edit your repository list:

vi /etc/apk/repositories

remove the "#" from the community repository, mine is:

http://uk.alpinelinux.org/alpine/v3.14/community

This is the final stretch. We've got bluetooth working and now we want to link bluetooth to the speakers

apk add bluez-alsa bluez-alsa-utils bluez-alsa-openrc
rc-update add bluealsa
service start bluealsa
bluealsa-aplay &

[https://github.com/Arkq/bluez-alsa Bluetooth Audio ALSA Backend]
[https://github.com/Arkq/bluez-alsa/tree/master/doc bluez-alsa doc]
[https://manpages.debian.org/unstable/bluez-alsa-utils/bluealsa.8.en.html man bluealsa]
[https://manpages.debian.org/unstable/bluez-alsa-utils/bluealsa-aplay.1.en.html man bluealsa-aplay]
[https://panther.kapsi.fi/posts/2018-11-17_linux_bluetooth_audio Bluetooth audio in Linux: ALSA and LDAC]

=See Also=
Raspberry Pi's blog on [https://www.raspberrypi.org/blog/how-to-play-sound-and-make-noise-with-your-raspberry-pi/ How to play sound and make noise with your Raspberry P]

There are lots of speaker and amplifier options:
* Raspberry Pi's [https://www.raspberrypi.org/blog/iqaudio-is-now-raspberry-pi/ IQaudIO boards]
* Pimoroni's [https://shop.pimoroni.com/products/audio-amp-shim-3w-mono-amp Audio Amp SHIM (3W Mono Amp)] and [https://shop.pimoroni.com/products/mini-speaker-4-3w Mini Speaker 4Ω (3W)]
* The Pi Hut offers this [https://thepihut.com/products/adafruit-i2s-3w-stereo-speaker-bonnet-for-raspberry-pi Adafruit I2S 3W Stereo Speaker Bonnet for Raspberry Pi (Mini Kit)] and the [https://thepihut.com/products/stereo-enclosed-speaker-set-3w-4-ohm Stereo Enclosed Speaker Set - 3W 4 Ohm]

Alpine Linux - User contributions [en]

Raspberry Pi Bluetooth Speaker