May 2022 – infiniteknowledge.co.uk

The aim is to have a number of buttons that can control the player. Main functions are:

Stop/Start player.
Next/Previous track
Volume up/Down
Select Genre. The RFID tag will select the genre.
Scroll through Albums from those available.
Play an album.
Control display
… Lots more.

Pirate Audio software gives a start, but I need to reverse engineer it to see how it works. First question is where is it located? How is it built? There is a lot of good documentation on the Mopidy site, but lacks the file locations I need to get my head round.

Only one hit for sudo find / -name rotencoder.py shows this location. Here are the relevant folders:

/usr/local/lib/python3.9/dist-packages/mopidy
/usr/local/lib/python3.9/dist-packages/mopidy_raspberry_gpio/
/usr/local/lib/python3.9/dist-packages/mopidy_iris 
/usr/local/lib/python3.9/dist-packages/mopidy_local
/usr/local/lib/python3.9/dist-packages/mopidy_pidi 
/usr/local/lib/python3.9/dist-packages/musicbrainzngs
/usr/local/lib/python3.9/dist-packages/pidi_display_pil
/usr/local/lib/python3.9/dist-packages/pidi_display_st7789
/usr/local/lib/python3.9/dist-packages/uritools

Make the files easier to remote edit:

sudo su

find /etc/mopidy -exec chmod o+w {} \;

find /usr/local/lib/python3.9/dist-packages/mopidy_raspberry_gpio/  -exec chmod o+w {} \;

find /usr/local/lib/python3.9/dist-packages/mopidy_iris   -exec chmod o+w {} \;

find /usr/local/lib/python3.9/dist-packages/mopidy_local /usr/local/lib/python3.9 -exec chmod o+w {} \;

find /usr/locallib/python3.9/dist-packages/mopidy_pidi -exec chmod o+w {} \;

find /usr/local/lib/python3.9/dist-packages/musicbrainzngs  -exec chmod o+w {} \;

find /usr/local/lib/python3.9/dist-packages/pidi_display_pil  -exec chmod o+w {} \;

find /usr/local/lib/python3.9/dist-packages/pidi_display_st7789  -exec chmod o+w {} \;

find /usr/localfind /lib/python3.9/dist-packages/uritools -exec chmod o+w {} \;

find /etc/mopidy -exec chmod o+w {} \;

Looking at the Pirate Audio installer script. It does the following:

Modify /etc/modipy/modpi.cont
Installs the following python libraries:
- python3-rpi.gpio- Extensions for GPIO
- python3-spidev- Extensions for the SPI interface used by display
- python3-pip- PIP installer
- python3-pil- Package installer for Python.
- python3-numpy- Package for dealing with arrays.
- libopenjp2-7 – JPEG and JPG200 image library.
- Enables SPI interface
- Modifies config.txt for GPIO pins and the DAC.
- Installs Mopidy and spotify plugins.
- Installs and updates modpi_iris for image display.
- Installs plugins for Pirate Audio:
  - Mopidy-PiDi
  - Mopidy-Local
  - pidi-display-pil
  - pidi-display-st7789
  - mopidy-raspberry-gpio
  - mopidy_iris
- Modifies the mopidy config file to configure the various modules:
  - raspberry-gpio – define pin mappings
  - file – specify where to find music files
  - pidi – specify display controller
  - mpd – music player daemon on local machine.
  - http – web server interface
  - audio – output audio device & volume
  - spotify – connection details

So now I start to see what is needed. I need:

mopidy_raspberry_gpio
Replace with mopidy_Chronos to map the IR to mopidy commands .
modipy local

Display is handled

Previous post showed how I stripped down a Pure Chronos CD/Radio and showed how the various buttons on the chassis were transmitted to the motherboard as a pseudo IR signal. Now its time to decode the signal on the Raspberry PI.

This article seems to be reasonably up to date:

https://www.digikey.co.uk/en/maker/blogs/2021/how-to-send-and-receive-ir-signals-with-a-raspberry-pi

Here is the circuit they use:

First step is to edit /boot/config.txt to specify the IO pins I am reading IR signal on GPIO pin 19.

dtoverlay=gpio-ir,gpio_pin=19 # for receiving data
##dtoverlay=gpio-ir-tx,gpio_pin=26 # for sending commands

Reboot:

sudo reboot now

Install some helper libraries:

sudo apt update
sudo apt install ir-keytable

Test:
This command will read IR reciever and print parsed commands.

sudo ir-keytable -c -p all -t

Investigate if this fails when you send some signals. After fixing incorrect wiring, I get something like this:

pi@raspberrypiMP3:~ $ sudo ir-keytable -c -p all -t
Old keytable cleared
Protocols changed to unknown other lirc rc-5 rc-5-sz jvc sony nec sanyo mce_kbd rc-6 sharp xmp cec imon rc-mm
Loaded BPF protocol xbox-dvd
Testing events. Please, press CTRL-C to abort.
246.860112: lirc protocol(nec): scancode = 0x8099
246.860168: event type EV_MSC(0x04): scancode = 0x8099
246.860168: event type EV_SYN(0x00).
246.920145: lirc protocol(nec): scancode = 0x8099 repeat
246.920207: event type EV_MSC(0x04): scancode = 0x8099

Yea, I can now read the various button presses from the Chronos chassis and read them with the RP. I could go further ans install the main lirc library, but enough for now. Time to reassemble the hardware and try to hack the music player software. Not sure if I will require LIRC as I dont need to translate the keycodes, but it may be helpful to get the data into the player software.

~~Install lirc for the main library:~~

sudo apt install lirc

~~Edit the configuration file so set the sensor up as a device:~~

sudo nano /etc/lirc/lirc_options.conf
... and add...
driver = default
device = /dev/lirc0

~~Reboot and test:~~

sudo systemctl stop lircd.service
sudo mode2 -d /dev/lirc0

~~… and so it goes on…~~

Month: May 2022

Hacking a Mopidy media player.

IR detection with Raspberry Pi