I am trying to sense and control devices. (ie. printer applicator, conveyor, on/off pushbutton,etc.) Does anyone know of a simple devices that convert contact voltages(on or off) to something VFP could understand by reading the serial port?

For instance: if signal from conveyor is on and pushbutton is off run this piece of code and tell printer applicator to apply.

Any ideas are greatly appreciated.
Thanks,
David Martin