I try to show you how you can connect npn sensor and setup repetier configuration for auto bed leveling.
This is my first project ,of course ı may have some mistake and some missing information however I regularly check the comment to help those who want to use auto bed leveling on their 3d printer :)
in generally we use in 3d printer NO and gnd at trigger about 5v.
There is a two type sensor ,pnp and npn.
when it connected to 12v ;
not trigger, give 8 -9 v which is ok for 3d printer
trigger, give zero volt , so everything is ok for 3d printer
when it connected to 12v, it gives 12v at trigger. so it will damage 3d printer.
if your pnp sensor is working when cennected 5v , it is ok , but not working you should reduce the output voltage to 5v or less and you change the firmware for pnp sensor.
I have experience in capacitive npn sensor and ı will mention about this type of sensor.
I buyed this https://tr.aliexpress.com/item/High-Quality-LJC18A3-H-Z-BX-Approach-Sensor-Cylindrical-Capacitive-Proximity-Switch-NPN-6-36V/32627840658.html?isOrigTitle=true