Cheap BED Level Sensor!! This will only use the sensor wires which don't really have much voltage (around 0.5v). Basically it's a very simple switch, when the 2 m3 screws touch together it signal the board.
Only need 2 m3 screws, 2 washers, one spring, 2 nuts and a print part! Total cost less then 1$ :)
Print the STL provided in this thing. This sensor mount is 12mm diameter, will be able to be mounted on compatible "inductive sensor" or you can screw it where you want using the 2 holes for that mater... I used 20% infill and with support.
Insert a standard nut inside the printed part on the top, then insert a 8mm m3 screw, don't forget to attach on of the sensor wire on this screw.
- You need a 20mm m3 screw (put something around that size), before insert the nut, the screw need 2 washers and one sprint, so, insert in that order, washer, spring, washer, the other sensor wire then screw inside the part on the lock nut.
With this sensor, when the leveling is done, it need to be removed to not touch the print, it is the only inconvenient but it work.
Test video: https://youtu.be/IfeVVwbapV8
If you have suggestion for some type of mechanism to be able to retract this sensor without unscrew post your comment :).