I have a small dedicated controller built around an Arduino that accepts commands from a PC over USB (serial). The communication is one-way — the controller never sends data back to the PC.
Now I need to extend the controller to handle more duties, but there's no room physically or program-wise, so I'm adding a second box with another Arduino that will accept the extended commands.
I can't alter the controlling PC application or add another USB port to the PC. The application controls the hardware and is in turn driven by a script. It can only talk to one serial port (physical or virtual) at a time. We can alter the script but not the hardware/application. So my hope is that I can just bridge across the D+/- lines to feed the second controller.
If this were straight serial I'd have no problem, but with USB in the middle I see issues ahead, because the PC will want to enumerate both Arduino USBs, right?
Is there a solution here I'm overlooking? Can I use USB passively, as a listener only, with the second controller?