shairport-power

Background

I recently got and old pair of speakers, and wanted to set them up to stream wirelessly with AirPlay. One of the best ways to do this with 3rd-party software seems to be to run shairport-sync on a Raspberry Pi.

However, it turned out that my speakers had a bit of a "hum" when no audio was playing, so I needed a way to switch them off when not in use. Also saving a couple of watts of power.

The finished product

(Youtube Video)

Ingredients

• Raspberry Pi 3 model B
• TP-Link Powerline Adapter
• Raspberry Pi Case
• A compatible Relay. I used a 4x relay block which I had lying around but really you just need a single one
• Some wires
• Some female connectors and plugs

Controlling the power

The starting point was this question which seemed to do something I wanted. Shairport-sync has a feature which runs a script when music starts or stops, and this was perfect for controlling the power.

I set up the python script to take an ON or OFF parameter and control the relay switch.

I used pins 4, 6, 8 and 10 on the Raspberry Pi (more convenient, as they're next to each other). Pin 4 supplies power at 5V. Pin 6 is ground, and pin 8 is the I/O for the switch. Pin 10 is connected to a second relay in case I decide to add something else to the system later on.

I ran the wires through the conveniently sized holes in the case, to keep them safe in case they catch on anything.

Then I set up the relay connection in a little plastic box on the other end.

And closed it up...

As you can see on the outside, I split the power cable to the speakers, and spliced the relay in the middle of the live wire.

Configuring the software

I chose the Python GPIO library because the pin state is retained after the script exits. This isn't the case with gpiozero (a popular, simpler alternative).

Finally I had to change some configuration parameters in shairport-sync to point to my scripts:

...
sessioncontrol =
{
  run_this_before_play_begins = "/home/pi/shairport-power/scripts/gpioControl.py ON";
  run_this_after_play_ends = "/home/pi/shairport-power/scripts/gpioControl.py OFF";
...

And restarted the shairport-sync service. On the first run this didn't work, with a syslog error:

RuntimeError: No access to /dev/mem.  Try running as root!

This requires a solution to fix permissions for the shairport-sync user. The following will grant the shairport-sync user permission to use gpio:

sudo adduser shairport-sync gpio

And then a system restart applies the change. Worked the next time around!