The purpose of this article is to lay out a way to use your computer
to pick [operate] pipe organ magnets and make music.  If this were a
cookbook there would be some missing ingredients and oven temperatures,
but I hope it will get you into the kitchen.  I'm not a MIDI expert, an
organ expert, a good musician or computer guru -- just someone who has 
worked through it.  My apologies if I've explained something grossly
wrong here, or explained something that already exists or made
something sound too hard or too easy.

Here's what we are going to do.  We're going to find music and some
software for our computer (PC) and have the PC send the music to a new
PC connection we'll need, a MIDI_Out port.  A MIDI cable will connect
the PC to the brains of this project, a box full of electrical things
called a MIDI decoder.  The MIDI decoder will control what magnets pick,
and if there is air when the magnets pick there will be pretty music.

MIDI

MIDI is short for Musical Instrument Digital Interface.  For purposes
here it refers to the music and the interface devices that connect
between your computer and the pipes.  The MIDI music is just a bunch
of data.  It is not sound like on an old 8-track cartridge machine but
rather digital instructions that, among other things, tell who to play
what note for how long.

All the MIDI connections are the same and use a cable with a 5-pin male
DIN connector on both ends.  These cables connect to female 5-pin DIN
connectors labeled either MIDI_In, MIDI_Out or MIDI_Through.  Things
like a computer or piano or accordion or saxophone can make music and
could have a MIDI_Out socket.

MIDI_In on your computer, piano, saxophone or pipe organ means it might
be able to do something with the MIDI data that came from a MIDI_Out
port, like play the notes or record it.  MIDI_Through means MIDI came
into a box through a MIDI_In connector, the box looked at the data,
maybe did something, then sent it undisturbed to the MIDI_Through
connection.

MIDI_Through is useful if you want to connect a bunch of things
together.  The way the MIDI data is sent you can connect a dozen things
together if you like, with one of them telling the other eleven what do
to.  They all look at the same data, but they only play the notes that
are assigned to them.

MIDI data can be put together so that it is all assigned to the same
channel or it might be set up so that some notes can be sent to specific
channels or instruments.  In my case, my pipes are Channel 1 and my
bells are Channel 2.  If I hook up a drum machine it has a channel and
if I hook up a MIDI piano it gets its own channel.  Each device then
only plays specific notes sent to that channel.

That's the end of my MIDI explanation, and maybe even an end to what
I know.  To learn more about MIDI Music try the Wikipedia, get a book
or search for on-line tutorials.

MIDI music is a data file with an extension of .mid  You can make
it from scratch, convert old piano rolls, play your MIDI piano and
record the MIDI data, or you can go find it on the Internet.  You can
do a Google search on MIDI music and you'll find music search engines
and music.  Like most of the Internet there is no end to it.

Here's a couple places I've found that have downloadable MIDI:

  http://www.breadsite.org/classic.htm 
  http://www.divtune.com/dtmid.htm#19 

To get started, go here:  http://www.newbonbon.com/bandorgan.htm 

This is not my site and we should remind ourselves to honor people's
music copyright notices.  A  MIDI tune will play in the background.
If you scroll down and left click on Carousel Mignon on that page your
PC will play Carousel Mignon.  You're playing MIDI on your PC.  If you
right click on it and pick save, your PC will ask you where to save it.
Pick a spot that you can remember where you put it and save it.  You've
now got a piece of MIDI music.  Unfortunately, although your PC can
play it, you can't do much else with it because your PC does not come
with a tool to edit it or get it out of your PC.

MIDI Editor or Sequencer

The MIDI Editor is a way to display or change the MIDI Data and a
Sequencer is a piece of software to play music.  Often one piece of
software does both.

There's all kinds of software, including Noteur, a free piano roll
editor at http://huizen.daxis.nl/~Ppaardekam/index.htm , some expensive
complicated software like Finale and more reasonably priced tools like
Cakewalk, and Power Tracks.  I did not find freeware that I was
comfortable with, but if you are into piano rolls, Noteur might be for
you.  I bought Power Tracks but this is not an endorsement.  I found
it, the price was fair and I thought it would work.  I wish I could
recommend a free staff-based MIDI editor, but I'm happy with Power
Tracks Pro from PG Music:  http://www.pgmusic.com/powertracks.htm 

Once you have an editor, you can not only play *.mid files on your
PC, but you can monkey with them, change notes, transpose it, change
channels, etc.  The problem remains, however -- you're still stuck
in your PC.  After you have music and software to play it, you need
a MIDI_Out port on your computer.  Computers have USB ports, printer
ports, serial ports, display ports, sound in and out ports, but almost
never a MIDI port.  You can get one.  The simplest is a device that
plugs into your PC's USB port and has a cord with a MIDI_Out connector.

MIDI_Out ports

The web site here,  http://www.videopete.com/midi/ has a wealth of
information on MIDI hardware.  I bought an MAudio Mini Sport Uno from
here  http://www.m-audio.com/products/en_us/Uno.html  It plugs into a
PC USB socket and has an MIDI_Out and a MIDI_In connection.  With Power
Tracks pro or another sequencer, you can change your audio from being
sent to the speakers in your PC to outputting to this new connector.
If you get this far and don't have any pipes, you can plug the MIDI_Out
into the MIDI_In on a keyboard, electric piano, accordion, drum machine
or saxophone and use your *.mid files on your PC to play some
instrument.  Now what you really want to do is connect to the pipes.

The MIDI Decoder

Here's the big problem.  Although your MIDI accordion or saxophone
might have a MIDI_In connection, your band organ does not.  This is
the science part that other people have taken care of.  We have the
technology.  What you need is a box that has a MIDI_In port and is
smart enough to pick the right magnets to let air to the pipes.  We're
going to call that doodad a MIDI decoder because it can decode what's
coming into the MIDI_In port and turn it into instructions for the
magnets.  This decoder controls the power to the magnets.  We are
going to pick the magnets one of two ways 1) pulling them to ground
or 2) sending them power.

Here's the way I did it.  All the magnets have 18 volts going to one
side of their coil all the time.  There is a big bus of 18 volts on the
magnets inside the air box.  The other side of each coil has a wire
that goes to the proper connection on the MIDI decoder.  When the
decoder wants a note to play, it turns on a transistor or relay that
connects that wire to ground.  The other way to do it is to ground one
side of all the coils and send a wire from the other side of each of
the coils to a decoder that puts voltage on the wire when the note
should play.

Once again, we have choices for decoders, all nicely displayed at the
site I noted before,  http://www.videopete.com/midi/  Note that these
are circuit boards, some come assembled and some do not.  Most of them
are a board you will have to mount in a box or rack and for all of them
you will have to do some wiring.  I have only seen one box, from Midi
Boutique, that has everything built into one box with plugs for power,
MIDI and connections to magnets.  I did some hand wringing before
I bought the GEMHut board,  http://www.gemhut.com/hmeproducts.htm  and
was happy enough that I bought a second for my bells.

Read about each of them and buy what's best for you.  Look at the
dollars per note. Think about what kind of flexibility each board has.
You notice that most of the decoders have a MIDI_In and a MIDI_Through
connector.  They don't make any notes.  All they do is accept MIDI
input, and do something with it like pick a bunch of magnets.

A note of caution.  When the magnets pick, current will flow.  Make
sure your decoder and wires can handle the current requirement.
Remember that current is just the voltage divided by the resistance
of the magnet.  If you pick with 18 volts and the coil is 100 ohms, you
are going to need to handle .18 amps.  Pick ten notes at once and you
got 1.8 amps on the bus wire.  Read what you can about the board and if
you have any questions ask the vendor before you buy.  Maybe you can
get the manual before you buy the board.  They were all very nice to me
when I sent them questions.

Power supplies

Old PC power suppliers have 5 and 12 volts and even a wire to turn them
on and off.  You can also use one of the bricks from that box full of
old power supplies you got.  Make sure it is the right voltage and
current.

Bookkeeping

With 40 notes, your gonna have at least 41 wires from your magnets to
the MIDI decoder.  Write down what you got going on.  Make a table that
shows the pipe note, its wire, the connector onto the decoder.  Keep
track of what you are doing.

Worrying about what notes to use

When you get this built, you will at times want to just download tunes
and play.  You don't want to build a bagpipe, but rather want to build
an instrument that has all the notes with complete octaves.  Plan on
using as many notes as you can and making the range as big as you can.
There are not many pieces that will play in less than 20 notes and of
course you can never have too many.  Do the best you can.  Most of the
boards will handle at least 64 notes.

The outputs on the board will be labeled in notes and octaves.  You
need to have the notes from the pipes to be connected to the correct
note in the decoder.  When the decoder plays a C2, you need the wire
connected from the C2 on the decoder to the pipe you call C2.  Although
you could do it like I did and just wire the notes up in order and move
octaves around later, there is a bit of a convention and you could wire
it all up right to start with.  The table at this link defines what
notes go with what MIDI numbers:

  http://www.harmony-central.com/MIDI/Doc/table2.html 

As long as the pipes are wired up in order with a C to a C, it does not
matter a lot.  When you get all done you can transpose the parts using
the MIDI editor to make them line up with the pipes.  That's all done
with software.

Doing this can challenge your woodworking, electrical, computer and
music skills but is one of the most rewarding things I could imaging
building.  Just do it.  I hope this is enough to get you started.

Bill Clark