Santibacanomc wrote: ... but what do I have to do so that Hauptwerk sends signals to this board?
So far as I understand it, and as I have no experience of illuminated pistons I might be wrong, the illumination of a piston simply indicates that this was the last piston pressed within it's own scope.
Since the arduino already knows this, it would seem unnecessary to request HW to return the information; the arduino should simply need to switch on the lamp when the piston is pressed and switch off any other lamps which are in scope.
I suppose there might be an argument for saying that the illumination of a piston should indicate that the combination associated with it is still valid, so it goes out if the combination is changed, through hand registration for example, but I don't think this the normal behaviour of real organs.
Pistons which toggle things like couplers are different though. I would expect that a piston toggling the 'great to pedal' should have its illumination reflect the state of the couple regardless of whether it was changed by a piston press or by hand registration.
Nick