Auto touch Z end-stop
https://www.youtube.com/watch?v=qci2Qgi7VGE
https://www.youtube.com/watch?v=rPaKn7kD2EA
http://www.youtube.com/watch?v=n8JjLbSEUFw
After hot-end touches bed, Z stopped
It better use with auto bed leveling system in marlin firmware.
My configuration for marlin