I'm new to Arduino and I have seen this on YouTube Android Midi Player - YouTube as I have a 22 keyless McCarthy fair organ and would like to do the same thing with it.
I have contacted the YouTuber and he said that he designed the hardware and software himself but didn't say how to make it.
He used the BT Midi out app for Android, the Arduino bit is a control board,Bluetooth board, SD card borad and a 5 pin midi socket.
I could the connect that to a J-Omega board to control the organ.
I assume that the Midi files are on the SD card and it sends the list of files to the phone and then you choose the one to play.
Any help, suggestions for hardware and code would be much appreciated.
From the start of the video I would also say the midi files are stored on the SD card in which case all that is required are control codes to be sent to the Arduino. The Arduino then sends the actual files through the midi connection. This can be done with the basic SPP Bluetooth modules like the HC-06 and HC-05 that use basic serial communication.
At the end of the video though, you see the lyric and time on the Android device so maybe he is sending the files by Bluetooth or he has feedback telling the Android device what part of the tune is playing.
Either method is possible.
The Bluetooth module in the video looks like it's a HC-05 or HC-06 but its hard to see clearly.
I would suggest you treat this as two (or three) different tasks. Get the Arduino controlling the instrument, then get a Bluetooth connection working, (get the SD card part working) and then put them together.