A little project that allows you to control the ALSA mixer using a rotary encoder and some open source libraries. Includes a systemd service definition for installing a service on startup.
py-gaugette (https://github.com/guyc/py-gaugette.git)
pyalsaaudio (https://github.com/larsimmisch/pyalsaaudio.git)
wiringpi (https://github.com/WiringPi/WiringPi.git)
Install py-gaugette and pyalsaaudio as python libraries, either through pip or using setup.py (see each project for instructions)
Copy volume_knob.service to /lib/systemd/system
To make the service startup automatically, run
sudo systemctl enable volume_knob.service
Make sure the pins referenced in volume_knob.py correspond to how your knob is wired.
Install the service, start the service, play some test audio (convieniently provided in test_audio/) and turn the knob. Enjoy the changing volume.