mpdlistenpy

This python script is supposed to run on a rpi and has the following features :

• Relay trigger : Watches a MPD instance for play/pause/stop states and activates a relay via GPIOs accordingly ; the usecase for this is powering on/off a pair of speakers only when something is running.
• OLED display : Drives a 0.96" OLED display (ssd1306) to display MPD status (volume, current artist, album, title...)
• Button input : watches GPIOs for button input ; I'm using 5 push buttons for controlling playback (previous, next, toggle playback, stop, menu) or browse the database and add stuff to the playlist.
• Potentiometer input : Watches a GPIO for estimating the resistance of a rotary potentiometer and set volume accordingly.

Setup

Software

1. Install the latest light version of Raspberry Pi OS and run it on the RPI model of your choice.
2. Install the following dependencies

Hardware

Overall GPIOs usage

| FUNCTION | GPIO # | | OLED | GND, 3.3V, 2(SDA), 3(SCL) | | 5 BUTTONS | GND, 7, 8, 9, 11, 25 | | POTENTIOMETER | GND, 3.3V, 23 | | RELAY | GND, 5V, 17 |

You can check these here : https://pinout.xyz/

Oled screen

Using the SSD1306 OLED screen involves a few steps described here :

https://luma-oled.readthedocs.io/en/latest/hardware.html

and here :

https://luma-oled.readthedocs.io/en/latest/software.html

Once you've gone through these steps, you should be good to go.

Relay circuit

We're using the circuit described on projects-raspberry.com :

Components

• 5V DC coil relay
• BC337 NPN transistor
• 1N4002 diode
• 1KΩ resistor

Diagram

source: https://projects-raspberry.com/raspberry-pi-driving-a-relay-using-gpio/

Buttons circuit

Dead simple way described here, using a common GND, and 1 GPIO/button :

http://razzpisampler.oreilly.com/ch07.html

The only difference is the addition of a resistor on the GND rail.

If you're short on GPIOs, there is a way to use a single GPIO for multiple buttons based on resistance described here :

https://www.instructables.com/RaspberryPi-Multiple-Buttons-On-One-Digital-Pin/

Potentiometer circuit

Using the 'step response' method described here (It's the same principle as in the link above), we can use an analog potentiometer to control volume.

The solution described in the previous link is not very accurate though, so we'll be using an alternative solution offered by abyz.me.uk :

https://abyz.me.uk/rpi/pigpio/examples.html#Python_pot_cap_py

Components

• 100nf Ceramic capacitor
• 5KΩ Potentiometer

Diagram

   3V3 ----- Potentiometer --+-- Capacitor ----- Ground
                             |
                             +-- GPIO 23

Instructions for use are in the source file. The library ('pot_cap.py') is included in this project for convenience.

You might have to install the 'pigpio' library though :

sudo apt install python3-pigpio

You can find out more about installing 'pigpio' here :

https://abyz.me.uk/rpi/pigpio/download.html

Optional steps

Installing the systemd service

• Copy the provided service file 'mpdlistenpy.service' to '~/.config/systemd/user/mpdlistenpy.service'.
• Update, enable and start the service as a user :

 # If you need to edit the path to the script
 # systemctl --user --full edit mpdlistenpy.service
 systemctl --user daemon-reload
 systemctl --user enable mpdlistenpy.service
 systemctl --user start mpdlistenpy.service

Automounting Samba shares on startup

source : https://root.nix.dk/en/utility-scripts/mount-samba-share-as-user

Automounting USB

https://gist.github.com/zebrajaeger/168341df88abb6caaea5a029a2117925