Hi Temple
I did a mp3 Trigger project in 2012 using a PICAXE 08M2 communicating by serial. I've copied the initial part of the code which gives some good pointers as to what is necessary to get it to work and operating considerations to take on board in developing your project.
The magic lines of code to communicate look like this:- in my case 'kount' is a variable which determines which track is needed to play
select case kount
case 1
serout C.2,T2400,("t",1) 'track 001
case 2
serout C.2,T2400,("t",2) 'track 002
etc
end select
'======================================================================================
'
' S I X T E E N C H A N N E L M P 3 T R I G G E R
'
'======================================================================================
' version 1.0 5th November 2012 © A.F.Bond 2012
'======================================================================================
' This program drives a Sparkfun MP3 TRIGGER v2 module to produce any one of sixteen
' sounds, arranged in two banks of eight on opposite throws of the transmitter joystick.
'
' Selection occurs by the user repeatedly 'jabbing' the joystick in the appropriate
' direction - three times for sound three, five times for sound five etc. On the chosen
' jab the user holds the joystick pressed to assert the sound. When the sound is heard
' to begin to play the joystick can be released. However, if the joystick is found to
' still be held when the sound has finished playing, the sound will be repeated - so
' for example, three blasts of a horn could be accomplished this way.
'
' The transmitter frame rate is used to time the joystick excursions and determine
' whether they are 'jabs' or a 'hold'. When a 'hold' is detected, the state of the jab
' counter determines which of the eight sounds related to that direction of jab is
' required. The jab counter is reset whenever a sound has been asserted or if the
' joystick has been in the centre position for more than a second (which far exceeds
' the regular jabbing rhythm pauses). The transmitter frame rate is measured during the
' start-up sequence and the jab/hold timing intervals adjusted accordingly.
'
'
' Users should arrange the sounds to be accessed in order of importance - for example a
' horn sound (when used for warning of imminent collision) should be activated by a
' single 'jab' rather than for example 7 'jabs'. Also consider assigning one sound to
' be a short period of silence, the effect of which is to act as a 'cancel' command for
' any long duration sound (such as background ambience) that is currently playing.
'
' The user may also set the volume level of the device duration normal operation by
' giving nine 'jabs' and a 'hold' which selects a seventeenth track (which ideally
' will last for 10 seconds or more) and all the time the 'hold' is maintained the
' volume gradually increases or decreases depending on the direction the joystick was
' operated. The joystick is released when the desired volume is attained and this
' setting is stored in EEPROM.
'
' The MP3 TRIGGER module is controlled by using its serial port at 2400 baud and this
' condition should be set up in an initialisation file named MP3TRIGR.INI which must be
' located in the root directory of the micro SD card. In the absence of this INI file
' the unit defaults to 38400 baud. The INI file contents must be as follows:-
'
' #BAUD 2400
' #STAT 1
'
' The latter command (#STAT1) configures the TRIG18 connection to become a status
' output rather than a trigger input and this status tells the micro-controller
' when a sound has finished playing (so that in the case that a repeat is required it
' can be re-triggered). If this command is not present in the INI file, then TRIG18
' will default to an input and deprived of status feedback the micro-controller may
' not function correctly.
' The firmware of the MP3TRIGGER should also be upgraded to the latest version (v2.53
' at the time of writing) which can be downloaded from
http://makerjam.com/support.
' You may have only just bought the unit but how long has it been in stock with an
' earlier firmware version installed? Amongst other things the latest version
' (reportedly) fixes a bug whereby occasionally at start-up, although tracks can
' be triggered, they play at zero volume, requiring a power cycle to correct the
' situation.
'
' From v2.4 onwards the file naming convention also changed to a more user friendly
' format, so again a firmware upgrade is recommended to ensure the information on
' file naming given below will work with your unit.
'
' File names must begin with a three digit number (using leading zeros) relating to
' the trigger channel required. Whilst numbers 001 to 255 are valid, in this 16
' channel implementation, users must employ numbers 001 to 016. The remainder of the
' filename can be anything (dots excluded). For example the following are both
' valid filenames for trigger channel 14 "014TRACK.MP3" and "014 Dive Alarm.mp3"
'
' There are two more special cases :- a file name beginning 255 will play immediately
' after power-up to signify that the unit is ready for use. A file name beginning 254
' should be assigned to a longish sound sample that is to be used for setting the
' volume.
'
' If files in the range 017 to 253 are loaded, they may be accessed manually by using
' the MP3 TRIGGER's 'jog' switch. The current design *could* be extended to access all
' 256 available sounds by the jab/hold technique, but it was felt that counting much
' beyond 8 jabs either way gets rather impractical.
'
' Even numbered files are accessed from jabs in one direction of the joystick and odd
' numbered files from jabs in the opposite direction.
' Note that if users have "hide known file extensions" option turned on in their file
' manager then typing in the following to rename a file "001 6 inch gun.mp3" will
' actually result in a file named "001 6 inch gun.mp3.mp3" which will not play!
' In this case just type "001 6 inch gun" and the original mp3 file extension will be
' appended automatically.
'
' mp3 tracks should be recorded at 128kbps or less (some reported playback issues at the
' specified max rate of 192kbps)
'
' Note the "earthy" side of the audio o/p jack socket sits at 1.25v DC and connecting
' directly to an amp whose 0v is common with the RC system's 0v will short the audio
' biasing and no sound will be heard. In this case use a 47uF capacitor in the 0v feed to
' the 3.5mm jack plug (+ve end to the mp3 trigger)
'======================================================================================
'
'======================================================================================
' PICAXE 08M2 CONNECTIONS
' leg 01 (Vdd) +5v
' leg 02 (serial in) connect to 0v
' leg 03 (IN C.4) rx input
' leg 04 (IN C.3) TRIG18 - configured as play status by ini file
' leg 05 (OUT C.2) serial out to RX of MP3TRIGGER
' leg 06 (C.1) unused
' leg 07 (OUT C.0) LED drive
' leg 08 (Vss) 0v
'======================================================================================