Running 5VDC signal a long distance
Your best bet is probably to use an opto-coupler at the remote end, and a constant current driver at the micro end.







simulate this circuit &ndash; Schematic created using CircuitLab

This effectively gives you a current loop interface which would be pretty much impervious to noise and distance provided the voltage supply for the LEDs is high enough to swamp the drop along the lines. It also removes ground from the equation, so it will not matter if the remote ground is significantly different from the ground at the micro.

You should, however, augment this design to include protection from ESD and other transients. (See my second circuit in this answer, but replace the relay with an opto-coupler.)

If the environment is electrically hostile and you wanted it to be really cool, you may be able to run fibre optics that far.