[Jimmy] at the aptly-named DIY and Digital Railroad channel has several videos on integrating railroad setups with Arduino ... The signal shifts from positive to negative to indicate marks ...

So I needed a way to map the RC receiver’s two sets of motor control wires, which can have either positive or negative voltages across them, to the Arduino pins which only want positive voltages.

YouTuber YellowRobot.XYZ has created a handy new pocket-sized gadget which is powered by Arduino and uses NFC tags to help you build positive habits ... corresponding LED lights on a gadget.