Additional information to make it easier for you to help me.
To make sure there is nothing wrong with the connection between the DIN chassi and the USB midi cable, I wired up the DIN with the piano DIN, as I said to make sure my DIN connection is working.
And my piano were able to play tones on the midi synth.
So there must be a problem with my circuit. I can notify on my arduino UNO that the TX led is going on and off.
Why am I not recieving any data from the arduino?