Implementation details of the RFID audio book reader for my blind grandfather

Last month I posted the RFID audio book reader I built for my grandfather (https://news.ycombinator.com/item?id=8177117). Many people asked me through different channels for more details on how I built it, so I took some time to write a small series of posts about the implementation.

The initial configuration of the Raspberry Pi and how I play the MP3 files using a local MPD server are described here: http://willemvanderjagt.com/2014/08/16/audio-book-reader-playing-mp3/

The setup of the RFID reader and how to read the cards in Python is here: http://willemvanderjagt.com/2014/08/17/audio-book-reader-reading-rfid/

How I handle events like button presses using interrupts and different threads in my code is here: http://willemvanderjagt.com/2014/08/19/audio-book-reader-interrupts-threads/

And finally, some last remaining details about unbouncing the buttons, and how the code for the status light on the front of the reader runs in its own thread, is described here: http://willemvanderjagt.com/2014/09/13/audio-book-reader-finishing-up/

I'm sure I'm leaving out details, so if there's anything you'd like to know, please ask and I'll be happy to answer.