Step 3: Setup the SparkFun MP3 Trigger
Program 9600 Baud Firmware (optional)
I wanted the MP3 Trigger to support 9600 baud for more controller flexiblity, so a friend reprogrammed the MP3 Trigger with new firmware. He found the firmware and instructions on the creator's website. To re-burn the firmware you will need a Cypress MiniProg.
Load Songs onto Micro SD Card
Copy songs over to a microSD card. The card must be formatted using FAT16. The songs support a constant bit-rate sampling up to 192kpbs.
The MP3 has three pins that are required to be connected to the IO-204 - GND, USBVCC, and RX. There is also a switch that should have "USB" selected. This will allow the MP3 trigger board to powered by the USBVCC pin. Connect the corresponding pins to the IO-204.
Control Playback and Volume
The serial protocol is simple. Send the serial string "O" to start / stop the MP3 player. Send "v%01" to set the volume to the maximum. To lower the volume send serial strings of "v%XX" where XX is a number between 01 and 40 - "01" is the loudest and "40" is really low.