Using an old keyboard is an awesome idea but I am doing this for local control at the controller. My controller is connected through an ESS (Ethernet Smooth Stepper) back to the computer. I do not want another USB connection back to the computer. I will send some pictures this weekend as I make more progress.
Everyone seems to be missing the point here about using a usb keyboard, with a key assigned to an input signal anything can be programmed into a function in the PLC script. Worried about wires then use a wireless one, an average board in one of those is about 30mm x 50mm, crossin a couple of wires activates a key, you will have to map which ones before removing the whole keyboard.
DazTheGas