Raspberry Pi Bluetooth Speaker: A Comprehensive Guide

This guide provides a detailed walkthrough on turning your Raspberry Pi into a Bluetooth speaker. You will discover how to use Yocto for building custom Linux distributions tailored to your specific needs. In the end, you’ll be able to stream music from your connected phone to your Raspberry Pi via the Bluetooth A2DP profile, with Pulseaudio managing the audio routing.

Prerequisites
- Hardware
- Software
Setup Yocto Environment
- Download Required Repositories
Setup Build Environment
Runtime Configuration
- System
- PulseAudio
- ALSA
- Bluetooth
- Optional setting
Debug
- PulseAudio troubleshooting
Conclusion

Prerequisites

Hardware

Raspberry Pi (tested on Raspberry Pi 3B+)
SD card
A speaker with 3.5mm jack
A BT USB dongle (recommended)

Software

Choose a Yocto release based on your demand. Please check Yocto Releases for more details. (tested on kirkstone)
Prepare your build host. Please see Yocto Project Quick Build and System Requirements for more info.

Setup Yocto Environment

Before building the custom operating system image, we need to set up the Yocto environment.

cd ~/
mkdir rpi-yocto-bsp 
cd rpi-yocto-bsp/

Download required repositories

mkdir sources
cd sources/

git clone -b kirkstone --depth=1 git@github.com:yoctoproject/poky.git

The general hardware specific BSP overlay for the RaspberryPi device.

git clone -b kirkstone --depth=1 https://git.yoctoproject.org/meta-raspberrypi

A collection of layers to suppliment OE-Core with additional packages, we will need a few layers from it.

git clone -b kirkstone --depth=1 https://git.openembedded.org/meta-openembedded

Setup Build Environment

Initialize build environment

source poky/oe-init-build-env rpi-build

Add required layers

bitbake-layers add-layer ../sources/meta-raspberrypi
bitbake-layers add-layer ../sources/meta-openembedded/meta-python
bitbake-layers add-layer ../sources/meta-openembedded/meta-oe
bitbake-layers add-layer ../sources/meta-openembedded/meta-multimedia

Build configuration files

conf/bblayers.conf:

# POKY_BBLAYERS_CONF_VERSION is increased each time build/conf/bblayers.conf    
# changes incompatibly
POKY_BBLAYERS_CONF_VERSION = "2" 

BBPATH = "${TOPDIR}"
BBFILES ?= ""

BBLAYERS ?= " \ 
  /home/eric/rpi-yocto-bsp/sources/poky/meta \
  /home/eric/rpi-yocto-bsp/sources/poky/meta-poky \
  /home/eric/rpi-yocto-bsp/sources/poky/meta-yocto-bsp \
  /home/eric/rpi-yocto-bsp/sources/meta-raspberrypi \
  /home/eric/rpi-yocto-bsp/sources/meta-openembedded/meta-oe \
  /home/eric/rpi-yocto-bsp/sources/meta-openembedded/meta-python \
  /home/eric/rpi-yocto-bsp/sources/meta-openembedded/meta-multimedia \
  "

conf/local.conf

Include the following packgages:

systemd: a system and service manager includes udev reponsible for detecting ALSA audio devices on the system.
PulseAudio: a sound server system for transferring audio to a different machine.
Bluez5: provides support for the core Bluetooth layers and protocols.
packagegroup-tools-bluetooth: includes bluetooth specific tools and PulseAudio modules for BlueZ at runtime.

MACHINE ??= "raspberrypi3-64"

DISTRO_FEATURES:append = " systemd pulseaudio bluetooth alsa"
IMAGE_INSTALL:append = " pulseaudio pulseaudio-server packagegroup-tools-bluetooth alsa-utils alsa-plugins bluez5"
DISTRO_FEATURES_BACKFILL_CONSIDERED += " sysvinit"
VIRTUAL-RUNTIME_init_manager = "systemd"
VIRTUAL-RUNTIME_initscripts = "systemd-compat-units"

Note

The alsa-utils package contains (among other utilities) the alsamixer and amixer utilities. amixer is a shell command to change audio settings, while alsamixer provides a more intuitive ncurses based interface for audio device configuration.
The alsa-plugins package enables upmixing/downmixing and other advanced features for high quality resampling.
alsa-plugins package is optional here.

Deploy image

Build Image

bitbake core-image-base

Flash image to SD Card

Replace /dev/sdX with the appropriate device identifier for your SD card.

bzcat ./tmp/deploy/images/raspberrypi3-64/core-image-base-raspberrypi3-64.wic.bz2 | sudo dd of=/dev/sdX bs=1M conv=fsync && sync

Runtime Configuration

Boot up your Raspberry Pi from the sd card.

System

Check Bluetooth Controller

$ hciconfig
hci0:   Type: Primary  Bus: UART
        BD Address: B8:27:EB:7C:97:71  ACL MTU: 1021:8  SCO MTU: 64:1
        UP RUNNING PSCAN 
        RX bytes:1639 acl:0 sco:0 events:107 errors:0
        TX bytes:3597 acl:0 sco:0 commands:107 errors:0

Check sound card kernel module is loaded

# lsmod | grep snd*
snd_soc_hdmi_codec     20480  0
snd_bcm2835            28672  0

PulseAudio

Load modules

Whenever a new sink or source appears, the module-switch-on-connect module will switch the default sink/source to be the new sink/source. It is optional to load this module or set default sink/source device manually.

$ vi /etc/pulse/default.pa

Add the following line:

load-module module-switch-on-connect

Refer module-switch-on-connect for more info.

Audio Playback and Latency configuration

vi /etc/pulse/daemon.conf

Add the following lines:

resample-method=ffmpeg
enable-remixing = no
enable-lfe-remixing = no
default-sample-format = s32le
default-sample-rate = 192000
alternate-sample-rate = 176000
default-sample-channels = 2
exit-idle-time = -1
default-fragment-size-msec = 15

Start PulseAudio daemon

pulseaudio --start

Check PulseAudio cards

Make sure that PulseAudio cards have been created for ALSA cards.

$ pactl list modules short

...
7       module-alsa-card        device_id="0" name="platform-bcm2835_audio" card_name="alsa_card.platform-bcm2835_audio" namereg_fail=false tsched=no fixed_latency_range=no ignore_dB=no deferred_volume=yes use_ucm=yes avoid_resampling=no card_properties="module-udev-detect.discovered=1"
8       module-alsa-card        device_id="1" name="platform-bcm2835_audio" card_name="alsa_card.platform-bcm2835_audio" namereg_fail=false tsched=no fixed_latency_range=no ignore_dB=no deferred_volume=yes use_ucm=yes avoid_resampling=no card_properties="module-udev-detect.discovered=1"
...

Refer module-alsa-card for more details.

Note

module-udev-detect will look for the supported cards and then select the profile you want automatically.

ALSA

Unmuting the channels

By default, ALSA has all channels muted. Those have to be unmuted manually. Unmuting the sound card’s master volume can be done by using amixer:

$ amixer sset Master unmute

Refer ALSA: Unmuting the channels for more details.

Bluetooth

Start Bluetooth

systemctl start bluetooth

Connect Bluetooth with Phone

$ bluetoothctl
[bluetooth]# agent on
[bluetooth]# default-agent
[bluetooth]# discoverable on
[bluetooth]# scan on
pair XX:XX:XX:XX:XX:XX
connect XX:XX:XX:XX:XX:XX
trust XX:XX:XX:XX:XX:XX

Check PulseAudio modules

module-bluez5-device is responsible for managing Bluetooth audio devices, while module-loopback creates a loopback audio connection, allowing audio to be routed from one source to another within the PulseAudio sound server.

Make sure these two modules are loaded:

$ pactl list modules short
...
22      module-bluez5-device    path=/org/bluez/hci0/dev_<MAC_ADDR> autodetect_mtu=1 output_rate_refresh_interval_ms=500 avrcp_absolute_volume=1
23      module-loopback source="bluez_source.<MAC_ADDR>.a2dp_source" source_dont_move="true" sink_input_properties="media.role=music"

List available Bluetooth A2DP audio sources

Make sure the audio source from a Bluetooth A2DP audio stream is identified.

$ pactl list sources short
     alsa_output.platform-bcm2835_audio.stereo-fallback.monitor      module-alsa-card.c      s16le 2ch 192000Hz      SUSPENDED
     alsa_output.platform-bcm2835_audio.stereo-fallback.2.monitor    module-alsa-card.c      s16le 2ch 192000Hz      SUSPENDED
     bluez_source.<MAC address>.a2dp_source      module-bluez5-device.c  s16le 2ch 44100Hz       SUSPENDED

List available audio sinks

$ pactl list sinks short
0       alsa_output.platform-bcm2835_audio.stereo-fallback      module-alsa-card.c      s16le 2ch 192000Hz      SUSPENDED
1       alsa_output.platform-bcm2835_audio.stereo-fallback.2    module-alsa-card.c      s16le 2ch 192000Hz      RUNNING

Optional setting

Set default sink/source devices manually

pactl set-default-source <index|name>
pactl set-default-sink <index|name>

Set the card profile as audio source device:

pactl set-card-profile <index|name> a2dp_source

Set Volume

Adjust the volume level of an audio sink in PulseAudio to 100%. Replace <index|name> with the appropriate sink index or name.

pactl set-sink-volume <index|name> 100%

Debug

PulseAudio troubleshooting

For connecting error, sound glitches or any other troubles, refer PulseAudio Bluetooth headset Troubleshooting.

Conclusion

By configuring PulseAudio and connecting via Bluetooth, you can now stream music wirelessly to your Raspberry Pi speaker.

Table of contents

Prerequisites

Hardware

Software

Setup Yocto Environment

Download required repositories

Setup Build Environment

Initialize build environment

Add required layers

Build configuration files

conf/bblayers.conf:

conf/local.conf

Note

Deploy image

Build Image

Flash image to SD Card

Runtime Configuration

System

Check Bluetooth Controller

Check sound card kernel module is loaded

PulseAudio

Load modules

Audio Playback and Latency configuration

Start PulseAudio daemon

Check PulseAudio cards

Note

ALSA

Unmuting the channels

Bluetooth

Start Bluetooth

Connect Bluetooth with Phone

Check PulseAudio modules

List available Bluetooth A2DP audio sources

List available audio sinks

Optional setting

Set default sink/source devices manually

Set Volume

Debug

PulseAudio troubleshooting

Conclusion