This is the code that drives the art project "Ceremony" (https://www.youtube.com/watch?v=tKj1CYT8b3c) by Anne Pfeifer (http://www.annepfeifer.com).

Ceremony is an art installation consisting of 9 wooden boxes that are mounted on a wall in an arrangement of 3 x 3. Solenoids within the boxes can hit the boxes that are lined with various materials which produces a special and different sound on each box. Since the boxes are mounted on springs, they generate great accoustics and keep bouncing, even when the solenoids are turned off.

The installation consists of multiple components of which the technical ones are covered here.

The core of the electronic part is a Raspberry Pi (Model B), equipped with an TP-Link WN725N USB Dongle. A stripped down headless version of raspbian is used.

The nine solenoids are driven by an MCP23017 which is connected via i2c to the RPi. The digital outputs are then amplified with MOSFETs and directly power the solenoids.

The WLAN dongle creates a special (protected) adhoc WiFi (hostapd + udhcpd) where the configuration can be performed via e.g. laptop or smartphone.

As input format, MIDI was chosen, so each note relates with a solenoid. This way, it is really easy to command the length and the timing of impulses. A player implemented in python parses the MIDI file and then commands the solenoids.