Mine comes tomorrow, hoping it's not too hard. I don't think you really program it, it's a matter of wiring it up properly.. only programming as far as I know is naming the files properly on the SD card

I know a number of people have used MP3 Triggers to customize their pinball machines sound, but no one of yet has documented the steps involved. It would be great if someone wrote up a tutorial and posted here for all to see.

The "programing" is naming the MP3s the names of the triggers.

You get 18 triggers per card, so you have to do some planning to get your ship straight.

Because you probably don't want the "one shot" sounds to interrupt the background song, you probably want 2 cards.

1st card (one shot sounds):

Switches 1 thru 12 - sounds
Pops - tie together for one sound
Slingshots - tie together
Inlanes - tie together
Extra Ball - call out that it is lit
Special - call out that it is lit
Tilt - growl warning

2nd card (looping songs or end sounds that cancel the loop songs):

Background song - seamlessly looping song
2x playfield background song - faster paced song loop
5x playfield background song - fastest tempo song loop
Game over - sound
Tilt ball over - sound
Center drain - sound
Outlanes - tie together sound

So to "program" the sounds we name the MP3

On card #1:

If the pops are on trigger #13 then the pop MP3 is named: 013_Pops.mp3
If the Slingshots are on trigger #14 then : 014_Slingshot.mp3
Repeat for all other switches....

On card #2:

Make the normal song the #1 trigger: 001_song.mp3
Make the 2x playfield song the #2 trigger: 002_song.mp3
Make the game over sound the #4 trigger: 004_GO.mp3

You can use the playfield switches to trigger some inputs, and playfield/backbox lights to trigger others (like game over or 2x playfield).

VID1900,

I though I read somewhere that it could be programmed as well to play more than one sound per trigger. So you could have a random (different) sound play each time the same trigger was hit.
But I could be wrong

No, you aren't:
http://pinside.com/pinball/forum/topic/first-look-ghostbusters-custom/page/5

You can have virtually limitless callouts and sound effects with the random function. You can set any of the 18 pins to pull from a bank of random mp3's which are separate from the files the other pins trigger. (ie. you could have 16 specific sounds/tracks and 2 pins that randomly pull from 20 additional sounds/tracks).

You have probably gone through all the sparkfun information, but the user manual was especially helpful for me since it discusses the use of an initialization file which is something you will definitely want to include if you plan on doing things like controlling the volume of certain mp3 tracks, looping, stopping tracks, etc.

http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Widgets/MP3%20Trigger%20V2.5%20User%20Guide%202012-02-01.pdf

If you have any specific questions regarding how to ground the switches, etc., then post them here and hopefully someone will be able to help out. Just to give you a heads up, be very careful working with the unit while it is on. I fried a unit simply by allowing a stray piece of solder brush across one of the ICs.

Fear not. If I can do it, anybody can do it.

It would appear the guy building the custom bioshock pinball is using three mp3 triggers controlled by a main arduino board:
http://poormanspinball.blogspot.com/2012/08/those-dirty-secrets.html

Some people might want to use phototransistors and detect when certain lights are illuminated.

This would allow electrical isolation too.

...and fail along with either the bulb or the lamp socket.

Of course it will.

But regular switches fail, diodes fail, it's pinball - pretty much everything fails.

If you are using LED lamps (other than CT reds), then it's going to be a long time between lamp failures.

I imagine a lot of the games being redone in this way are older games. A LOT of those older games have garbage Bally sockets. This would require a new socket on each spot used for sure. I'm not against the idea. I would prefer to find a way to trigger on the voltage to the lamp, though, rather than the light coming from it.

You can do that too, of course.

You want to isolate the two circuits, so maybe diodes or optoisolators depending on your skill set.

Yes, many people restoring Ballys automatically replace the sockets, especially if they are the plastic ones.