It’s been a long time since I’ve written about my Raspberry Pi Whole Home Audio Project.

Simply, that’s because I’ve hit a bit of a wall and I’m especially busy with work right now so I haven’t been able to find the time to work my way around it.

The problem is that the USB WiFi adapters that I bought (for about $5 each) don’t perform well. They have signal strength issues, and while they do work and maintain a network connection, the poor signal strength means the connection isn’t fast enough to stream audio. There are plenty of other people out there having the same problem. You get what you pay for, I guess, and I need to buy replacement adapters.

I’m also considering a change in direction. My original plan was to install mopidy on one of the Pis and use pulse audio to stream the output to the others.

I’m considering instead installing TuneBlade on one of my Windows PCs. TuneBlade takes all the audio output from that computer and streams it using Apple’s AirPlay protocol. I’d then install ShairPort on all the Pis to turn them into AirPort receivers.

What do you guys think?

It’s very rare that I tweet teasers to my blog post, but
last weekend I was so excited to be making progress on my Raspberry Pi Whole
Home Audio project that I told the world I’d be publishing this one on
Thursday.

DIY #RaspberryPi Whole Home Audio system is progressing! Latest blog post coming Thursday… http://t.co/0FaPcSeDEc pic.twitter.com/syEMoG24Gm

— Jason Williams (@JayWll) February 9, 2015

Here we are on Friday morning. There’s doubtless a lesson in
here for me about making promises I can’t keep, but I’m hoping you’ll forgive
me when you read about what I’ve done.

If you’ve been following my #RPiWHA Project
hashtag on this blog then you’ll know that when we left off last time I had
three Raspberry Pis networked together with synchronized clocks, and one of
them had access to the internet and the music library I keep on my home server.
That’s important, but not especially exciting. Today we’re going to move in a
more exciting direction, though.

Today we’re going to put Pis #2 and #3 aside, but we’re
going to get Pi #1 playing music!

Specifying and Testing the Pi’s Audio Output

The Raspberry Pi has two options for audio output. It has a
3.5mm analog output, and digital output through its HDMI port. It decides which
output to use automatically – if you have a HDMI monitor plugged in then the Pi
will detect this and assume you want to use HDMI for audio too.

That’s not the situation for me (my Pi is “headless” and
doesn’t have a display connected at all), and audio comes out of the 3.5mm
output automatically – which is what I want. If you need to specify, you can
run:

sudo amixer cset numid=3 1

The digit 1 at the
end means the Pi should use the analog audio output. Putting 0 there instead would mean auto-detect
(the default) and putting 2 would
mean digital output over HDMI.

Plug in some headphones or speakers and run:

aplay /usr/share/sounds/alsa/Front_Center.wav

You should hear a voice saying “front centre.”

Install Mopidy

We’re going to install music playing software called mopidy.
It provides a web-based interface so you can control your music, or there are
controller apps available in your app-marketplace of choice. Mopidy’s website
takes you through the
install process in detail, but I’m going to summarize the commands here:

wget -q -O - https://apt.mopidy.com/mopidy.gpg | sudo apt-key add -
sudo wget -q -O /etc/apt/sources.list.d/mopidy.list https://apt.mopidy.com/mopidy.list
sudo apt-get update
sudo apt-get install mopidy python-setuptools

Done! We now have a basic install of mopidy, and the especially
astute amongst you will have noticed that we’ve also installed a package called
python-setuptools. Mopidy is written
in the python programming language, and the latter package is going to help us
with installing and setting up some mopidy extensions in an automated way. The
first thing we’re going to do is install something called pip, which is a tool for installing python packages:

sudo easy_install pip

Now that we have that, we’re going to in turn use pip to
install some mopidy extensions:

sudo pip install Mopidy-MusicBox-Webclient
sudo pip install Mopidy-WebSettings

With those commands we’ve added a web-based interface to our
player so we can control it from a browser on another computer or mobile
device.

Setting Up Mopidy

We’re almost ready to start mopidy and try things out, but
there is a little bit of initial setup to be done first. Edit the file ~/.config/mopidy/mopidy.conf. In the http section, change the following line
so that the web interface becomes accessible to any device on your network:

hostname = ::

In the local
section, tell mopidy where it should find your music library. In my case:

media_dir = /mnt/music

Save the file and exit. The next step is to tell mopidy to
scan your music folder:

mopidy local scan

If, like me, you have a large music collection stored on a
network share, be prepared for this to take a very long time. I started it
running before I went to bed, and it eventually completed the process about 45
minutes after I got up the following morning.

When it’s done though, we’re ready! Run mopidy:

mopidy

It’ll take a little while to fully start up, but when you
see the line

INFO     HTTP server running at [::]:6680

that means we’re good to go. Open the browser on your
computer or mobile device and point it to
http://192.168.1.71:6680/musicbox_webclient (replace 192.168.1.71 with the IP
address of your Pi as appropriate). Go to Browse, Local Media, and select a
song!

If all is well the music will be playing through the
headphones or speakers attached to the Pi, and we’re all done until the next
installment – rerouting the audio from Pi #1 and streaming it, synchronized, to
Pis #2 and #3 instead.

Enjoy!

At the start of the month I announced my plan to try and build my own whole home audio system using a handful of Raspberry Pis to act as the player and audio
receivers. I’ve received
all the stuff I need now, and I’m ready to get to building!

The first thing I’m doing is preparing the Pis and setting
up networking. Next I’m going to install audio playing software with a
web-interface on Pi number one, and thirdly I’ll adjust the setup so that this
player sends it’s audio to the other two Pis (the receivers) instead of
outputting it directly to its own speakers. You can follow the whole journey by
following the #RPiWHA
Project hashtag right here.

Installing Raspbian

Raspbian is the Raspberry Pi’s recommended operating system.
There’s plenty of guidance online on how
to install it, so I won’t reiterate the whole process here. When I ran
through Raspbian’s initial setup options on first boot I set my location,
timezone and keyboard layout (in Internationalisation Options), set the memory
split to 16mb for graphics (in Advanced Options – we can set this low because
we won’t even be connecting a display) and finally expanded the filesystem
(right from the main menu).

Minimizing SD Card Access

The Pi has no power button. If it’s plugged in then it’s on,
and you turn it off by pulling the plug. I’ve read online that if the power is
pulled while the system is in the process of writing to the Pi’s SD card (which
is the only storage the system has) this can cause problems and possible
corruption.

Linux systems do a lot of logging, most commonly to the
folder /var/log. They also write stuff about running process to the folder
/var/run. To minimize writes to the SD card, we’re going to mount these two
folders in memory instead of on the card. Another cause of frequent writes is
that linux systems store the time that a file was last accessed, so even if we’re
just reading a file the system is actually writing back to the disk to update
the time that the file was accessed. We’re going to change that behaviour too.

To make these changes, we’re going to edit the file
/etc/fstab so that it looks like this:

proc            /proc           proc    defaults          0       0
/dev/mmcblk0p1  /boot           vfat    defaults,noatime  0      2
/dev/mmcblk0p2  /               ext4    defaults,noatime  0      1
none            /var/run        tmpfs  size=1M,noatime   0       0
none            /var/log        tmpfs  size=1M,noatime   0       0

The first two lines haven’t changed, but on the third line
we’ve added the flag “noatime” to indicate that we don’t want to store the
timestamp that the file was last accessed. The fourth and fifth lines are
entirely new, and these create 1mb partitions in RAM to house the /var/run and /var/log folders respectively.

Setting Up Networking on Pi #1

The next step was to connect one of the Pis (and only one)
to my existing home WiFi network. To do this I plugged in one of my USB WiFi
adapters and modified the /etc/network/interfaces file to include the
following:

auto wlan0
allow-hotplug wlan0
iface wlan0 inet static
wpa-ssid MyHomeWiFiName
wpa-key-mgmt WPA-PSK
wpa-group CCMP TKIP
wpa-pairwise CCMP TKIP
wpa-psk MyHomeWiFiPassword
address 192.168.1.71
netmask 255.255.255.0
gateway 192.168.1.254
dns-nameservers 192.168.1.53 192.168.1.254

Your setup will probably be slightly different, but
essentially this connects to my home network, gives the pi a static IP address
(192.168.1.71 in my case) and defines my two DNS servers.

You may be wondering why I’m only doing this on one of the
Pis, given that they all need to be connected together. The reason is that this
first pi (the player) is ultimately going to be sending audio out over the
network as multicast packets. In other words, this data goes to every device on
the network whether they want it or not.

The problem is that this is a lot of data flowing around, and
a typical home WiFi network struggles under the load of it all. My solution is
to have two WiFi networks. The one we’ve set up above will connect us to the
internet (for streaming audio services) and other stuff on my network (like the
fileserver where my music collection lives), but we’ll use a second, separate
WiFi network to send the multicast audio to other Pis.

Let’s plug in a second USB WiFi adapter to the first Pi, and
make some more additions to the /etc/network/interfaces file:

auto wlan1
allow-hotplug wlan1
iface wlan1 inet static
address 192.168.5.1
netmask 255.255.255.0

This section is pretty minimal as you can see, but it’s
setting a static IP address on the second wireless interface. The important
part is that this uses a different subnet to the other WiFi network (in my
case, 192.168.1.x is my existing network, 192.168.5.x is the dedicated network
for the Pis).

This section of the /etc/network/interfaces file is so short
because this Pi is going to act as a wireless access point that the others will
connect to. To set this up we need an additional bit of software, called
hostapd. Because I’m using WiFi adapters based on a Realtek 8188 chipset, I had to download and compile this myself – the version found in the debian software repositories wouldn’t work for me:

wget https://github.com/jenssegers/RTL8188-hostapd/archive/v1.1.tar.gz
tar -zxvf v1.1.tar.gz
cd RTL8188-hostapd-1.1/hostapd
make
sudo make install

Then edit the file /etc/hostapd/hostapd.conf to change the following three lines:

interface=wlan1
ssid=PiWHA
wpa_passphrase=mySecurePassword

Finally, start the service and add it to the boot autostart services for future:

sudo /etc/init.d/hostapd start
sudo update-rc.d hostapd enable

Setting Up Networking on the Other Pis

We want the other Pis to connect to the wireless network
hosted by Pi #1. To do so, plug one USB WiFi adapter into each and modify the
/etc/network/interfaces file on each to reflect the following:

auto wlan0
allow-hotplug wlan0
iface wlan0 inet static
wpa-ssid PiWHA
wpa-key-mgmt WPA-PSK
wpa-group CCMP TKIP
wpa-pairwise CCMP TKIP
wpa-psk mySecurePassword
address 192.168.5.2
netmask 255.255.255.0

The important point here is that the IP address for each
must be unique, and must be on the same subnet (192.168.5.x) that we set on the
first Pi.

Setting Up Time Synchronization

The Raspberry Pi has no real-time clock, and instead it gets
the time from internet time servers at boot. Having the time synchronized on
each of our Pis is going to be important to make sure that they play music in
sync. Only the first Pi has a connection to the wider internet though, so we
need to take some additional steps. On Pi #1, edit the file /etc/ntp.conf and
uncomment (or add) the following line:

broadcast 224.0.0.1

This tells the pi to broadcast a time signal out onto the
network using a special multicast IP address that the other Pis will listen
for.

On the other Pis edit the same file, but uncomment (or add)
the following lines:

disable auth
broadcastclient

We don’t need to tell the other Pis which multicast IP
address to listen for – they already know as part of the NTP protocol.

And We’re Done! Or Are We?

That was a lot of setup work, but we should now have our Pis
setup and networked together, with our player device having an additional
connection to the wider internet.

The thing is… I don’t. The setup is all correct, but the
cheap USB WiFi adapters I bought from China don’t properly support access point
mode. Sometimes things work, sometimes they don’t.

I’ve read that I can download driver source-code from the
adapter’s manufacturer and compile the driver myself, so I’m going to try this
before I go further.