Help with LEDs on model railway project

[UKHeliBob]

This is probably what @wildbill is thinking of

Practical uses of nRF24L01 wireless modules?

I just bought a few nRF24L01 modules, although I have no project in mind. I used Library Manager to install the RF24 library of TMRh20 and tested them with the GettingStarted example that came with the library. (For those who've not seen that, all it does is get micros() on ArduinoA, sends it to ArduinoB for an echo back, gets a new micros() on ArduinoA and reports the trip time. Nothing fancy, but proves it works.) Next step is to add code at each end to (say) generate a random number on Ardui…