raspberrypi.org/magpi The Official Raspberry Pi Projects Book 27
SELF-PLAYING PIPE ORGAN Projects
>STEP-01
Wooden pipes
Each of 42 wooden
pipes produces a
different note. While
larger usually means
lower, some of the
bottom notes are
produced by shorter
pipes containing an
airtight stopper to
reduce the pitch.>STEP-02
Solenoid valves
Solenoids are used to open and close the pipe
valves to play and stop notes. O-rings prevent them
from sticking in the on position, while also stopping
the plungers making a clacking noise.>STEP-03
Wind chest
The wind chest features a weighted hinged door
which shuts automatically when many pipes are
playing, in order to boost the air pressure. The wind
is provided by a Kooltronic KBR125 blower.MAKING SWEET
PIPED MUSIC
user interface for selecting music
to play, it converts the MIDI
binary files into delay2note-on2
note-off commands, plus musical
directions: “The Raspberry Pi
takes into consideration tempo
changes and any other subtleties
in note timing, and converts them
into a number of microseconds,”
explains Wendell. “In this way,
the Pi has done all the heavy
lifting as far as calculations go.”
Another Python program is then
used to send this data to the
Arduino via USB.
While the high-tech side of the
project proved fairly hassle-free,
the physical engineering was more
problematic. Rne diL·culty was
the wind pressure regulator, which
originally had a bellows-type
mechanism. “I was trying out a few
different designs, trying to develop
one that was mechanically simple
and dependable while producing a
very stable pressure.” Fortunately,
Wendell’s friend Jim, a retired
HVAC engineer, stopped by and
suggested a new approach, using a
weight-controlled door as used in
ventilation systems. “I whipped up
a sample in about 20 minutes and
it worked a treat.”
Another issue involved the
spacing of the pipes, which
Wendell discovered could interact
with each other if placed tooclosely together. “I suddenly
understood why organs were
designed with the pipes in a few
rows but spread out, not bunched
together.” He also reversed the
overall layout to put the solenoids
at the front, so listeners can see
them operating the valves. He
has since added some LEDs: “It
makes it much easier to follow
what’s going on than just watching
the solenoids.”
The finished pipe organ
generated a lot of interest from
attendees at the Orlando Maker
Faire. “I think most people were
able to walk away with some
level of insight as to how the
combination of the old technology
of the pipe organ and the new
technology of the computer and
microcontroller fit together.ĤThe Raspberry Pi takes into
consideration tempo changes
and any other subtleties
Above A home-built driver board with
transistors is used to boost the power from
the Arduino output to trigger the solenoids