I'm hoping to start a discussion of people's favorite ways of using & mounting hall effect sensors for limit switches / end stops. Attached is what I did for my build. It's main claim to fame is that the sensors and magnets are "hidden". You have to look hard to find them. The ZIP file has a detailed explanation of what I did, my BOM (including sources) and the data sheets for the sensors mentioned. Also, I ran into what appears to be the holy grail of hall effect limit switches. The Allegro A1125 operates from 3.0V to 24V and is "normally closed" (the output is low unless it's near the magnet). Haven't tested them. Also, they're about $2 from Digikey so they're not the cheapest hall effect sensor out there.