Wiring 24v NPN Proximity Switch to 5v BOB - Why does'nt it work

[Neale]

These proximity switches come in so many flavours. The switch the OP is using switches to ground and an internal resistor makes no sense; the switch in the previous post switches to the supply rail and maybe an internal resistor is more useful.

If you use the NC version of the OP's switches, wired as suggested in series with the BOB input, you can connect a number of them to a single input. I have tested four in series, using 24V and a CSMIO, and that seems to work fine. Using the OP's NO switches, you would have to wire them in parallel but you lose the "fail safe" feature of NC switches.