You want to use the JohnSL FSR Endstop Controller, get it on Ebay pretty cheap, they even sell whole kits that include the 3 FSR's. This controller allows you to just wire the three FSR to the controller board and then have 2 wires going to the Z min endstop location as normal. No firmware changes or anything, the controller board takes the resistance readings from the FSR's and converts that to a High/Low signal for your printer controller. Pretty Slick! Happy Printing Everyone!!!