I was trying to create a midi device by following this tutorial Code Tinker Hack: How to turn Piano toy into MIDI keyboard (using Arduino/Atmega)
but using hairless-midiserial instead of soldering a midi port to it, but when you see the program open, all the keys are played at the same time
code?
circuit?
We can't guess these things you know!
The code in that link is a bit rubbish. He initialises an array a single value at a time in the setup function. If he were any good he would have done it correctly in a few lines at the start of the program.
It looks like the code is outputting the keyboard scan rather than when it detects a press.
Now have you changed anything?
Can you show a schematic of your wiring and a photo of it?