I have a musical keyboard (Casio CTK3500) which has an USB B to A output. I want to know a way to connect one (or more) of the wires from the USB cable to Arduino so that it can detect when a key is being played on the keyboard (maybe by detecting a voltage change, but I cannot seem to detect enough voltage change to do that).

I don’t need to know which key is being played or anything like that. I just want to detect when a key is being played on the keyboard.

Any help is much appreciated.