Assemble the HAT

In the Justboom Amp Zero box you’ll find:

• Amp Zero pHAT
• DC barrel jack adapter
• IR receiver
• 4 spacers with screws

To connect the Amp Zero to a Pi Zero, you’ll need to solder standard male header pins on the Pi. After having screwed on the spacers, the pHAT slides on top of the header pins, onto the Pi Zero.

Configure The OS

We’re using the latest Raspbian image because we need the Scroll pHAT software and some custom scripts to run. It’s easy to enable support for the Amp Zero – just add or comment following lines in the /boot/config.txt file:

#dtparam=audio=on
dtoverlay=justboom-dac

Setup Scroll pHAT

The Scroll pHAT is used to display the spectrum of the audio. To feed the spectrum analyser with an audio stream, we need to create a loopback device by modifying the ALSA config in /etc/asound.conf:

pcm.dac {
  type hw
  card 0
}

pcm.both {
    type route;
    slave.pcm {
        type multi;
        slaves.a.pcm "plughw:0,0"
        slaves.b.pcm "plughw:Loopback,1,0"
        slaves.a.channels 2;
        slaves.b.channels 2;
        bindings.0.slave a;
        bindings.0.channel 0;
        bindings.1.slave a;
        bindings.1.channel 1;

        bindings.2.slave b;
        bindings.2.channel 0;
        bindings.3.slave b;
        bindings.3.channel 1;
    }

    ttable.0.0 1;
    ttable.1.1 1;

    ttable.0.2 1;
    ttable.1.3 1;
}

pcm.!default {
        type plug
        slave.pcm "both"
}

ctl.!default {
        type hw
        card SB
}

So, by default, audio is sent to output device “both”, which consists of two outputs: the DAC and a loopback device. The loopback device’s counterpart will then be used to feed the stream to the spectrum analyser.

Setup Spectrum Analyzer

Next, you’ll need to get the modified code that visualises the spectrum on the Scroll pHAT from GitHub.

To take into account possible spectrum analyzer crashes, use this script to restart it in case it stops running running.

sudo modprobe snd-aloop
 
sleep 5
 
while true
do
  if ps aux | grep -v "grep" | grep "spectrum" 1>/dev/null;then
   sleep 1
  else
   sudo /home/pi/spectrum.py &
  fi
 
done

The Enclosure

And that’s the electronics sorted. Now it’s all the about the enclosure. To get those brain juices flowing, check out how Frederick made his wooden spiral enclosure for a spot of inspiration.

With your mind open to the possibilities for a creative enclosure, there’s no stopping you. But don’t forget to let us know what you build.