This is what I have done in the past, See image.
My switches where 500ma rated gold plated contacts and limit switches are 10amp rated(minimum current for these to work correctly is 50Ma) and I use 8 of them, the system runs from 24V (could be 12V) and I used 3 1K5 resistors in parallel to create 50Ma current draw (this is to make sure good contact is made) A zener diode to clamp and a schottky diode then a 4K7 pull resistor and then 100K current limiting resistor with a 100N as the filter, I've found this very reliable and my cable length is about 10 meters and it has never suffered any problems or incorrect press detects, Also in the code is some debcounce routine. On checking with the scope the signal to the Arduino is very clean. Also carried out noise test's and induced 100-1000khZ noise on the line and still a clean signal and no issues. The 3 resistors and switch are mounted off the PCB, At the end of the 10meters of cable)
Comments welcome.
