This is a modified version of the original RepRapPro Z end-stop for use with the Hall-Θ hall effect sensor.http://reprap.org/wiki/Hall-%CE%98Install using a 10mm and 30mm screw. Place nuts behind the Hall-O PCB to prevent strain.Hall-O with Melzi electronics To get the Hall-O end stop working with the Melzi electronics attach a resistor to the base of an NPN transistor and connect the resistor to the digital signal wire from the Hall-O. The other two legs then slot into the Z end-stop connectors on the Melzi board. Power for the sensor can be taken from the ISP connectors in the bottom right of the board. See attached image.