You can build your own limit switch. The picture
below shows a homemade switch next to the Lego sensor switch.
Consider the instructions below as guidelines. This project is esay to modify to parts you may have on hand.
Before you start this project, read and understand the theory of limit switches.
If you prefer, Techno-stuff sells an adapter that lets you use Lego switches as limit switches.
Switch - Hosfelt 51-374
Lego motor wire (#5111)
2x2 Lego brick
2x2 Lego plate
There is nothing special about the switch, except it must have normally closed contacts. You can use any switch that is easy to press and can be mounted in or on a lego piece.
Use a lamp or electrical tester to find the terminals that are normally closed. (Terminals are connected when the switch is not pressed) Solder a diode across these terminals.
Cut a Lego motor wire to the desired length. Attach the wires as shown.
Tape or heat shrink the wire junction that is not attached to the switch.
Insert switch into Lego brick, and glue in place. Glue on the bottom plate.