He wrote us describing it with these words:
This takes RFID tags each one mapped to a note and instrument and placed on one of 32 pegs will generate a music sequence. I designed and built a special RFID reader that has 32 read positions, it took 3 months to wire up. The case was hand built and it was designed to fit exactly into a flight box. It contains an Arduino and outputs MIDI.
It uses 32 red / blue LEDs to illuminate acrylic pegs which light up red when a token is hung on them. The sequence sweep progress is shown in blue on the pegs when the sweep position meets a peg with a token it light up purple and a note is produced. The sequence length can be adjusted from 8 steps to over a million steps before repeating.
You can browse his well-documented page with software and schematic at this link.