Matt Brailsford combined an old cassette player with a Raspberry Pi. When you insert a cassette (that has has an NFC tag associate with a playlist), it streams music from Spotify.
Inside the cassette player, all the standard components have been removed and in their place a Raspberry Pi and several helper modules have been added: an NFC tag reader, which you can just see through the hole in the metal frame top left — the red printed circuit board (PCB); an amplifier which is the blue PCB below that — the original volume potentiometer is connected to this to control the volume; and a custom circuit board to connect the buttons of the cassette player to the Raspberry Pi's General-purpose input/output (GPIO) via micro switches glued beneath the buttons.
This Raspberry Pi cassette player plays Spotify tunes