I have a digital piano Yamaha P-35 at home, which is midi compatible. I'd like to connect it to my computer in order to record me, or use my piano with some software. But I have no midi interface, and it looks really expansive. We can find some cheaper, but I do not trust them.
So I thaught that if I could build my own midi interface with my Arduino board, before to buy a "real" midi interface it would be great !
So that's y question : Can I build a midi interface thanks to my Arduino board, or will it be too hard or expansive ?
And yes, you can build one with arduino, I didn't try it, but: http://www.dimitridiakopoulos.com/hiduino
Then you have to add MIDI IN with an optocoupler like 6n13x or 4n28
The easiest way is to buy a midi shield or breakout from Sparkfun. You may wish to connect it to a different serial port. Use the MIDI library; the new version works with soft serial, thou I havn't tried that (I use a mega, which has 4 hardwired ports).
There are plenty of designs for making your own, but buying the composents could cost you more in the end if you don't have some already. Use a 6N136 optocoupler or equivalent. The ones given in the midi specifications tend to be too slow and unreliable, depending on the make and batch - this may explain the difficulties you read about on various forums.
As usual, the best way to write software is to adapt the examples and the numerous applications you can find on the web. Mine's on www.music.chrblee.net.