I hate using unnecessary wires.The other sensors use 3- 6 additional wires to connect routed to the ramps/MKS board.An inductive sensor is heavy and cable is big and heavy too.So in order to avoid that I designed a DIY Touch-MI Z-probe for auto-leveling a 3d printer without wires.
Description:
The signal from an optic probe(DIY touch-Mi) is sent wire less via an infrared light (IR diode) to an infrared sensor connected to a 3D Marlin board on the z-end switch connector.
The power for Z-probe and IR led is coming from 12V power supply of the hotend fan.

Materials:

• Optical endstop switch.
  https://www.ebay.com/itm/Optical-Endstop-Durable-RAMPS-1-4-Board-End-Stop-Switch-For-3D-Printer-CNC/264371544080?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D20190212102350%26meid%3D183188f7aeae4c2b9d0b626a4f047fd1%26pid%3D100012%26rk%3D3%26rkt%3D12%26sd%3D183807009527%26itm%3D264371544080%26pg%3D2047675&_trksid=p2047675.c100012.m1985
• Infrared Obstacle Avoidance Sensor For Arduino.
• Infrared LED(recuperated from the Infrared Obstacle Avoidance Sensor)
  or from any TV remote control.
  https://www.banggood.com/Infrared-Obstacle-Avoidance-Sensor-For-Arduino-Smart-Car-Robot-p-72965.html?cur_warehouse=CN
• 5mm dia magnetic ball -1pcs.
  https://www.google.com/search?q=5+mm+magnetic+ball&tbm=isch&source=univ&sa=X&ved=2ahUKEwik0oKkv7_iAhUxmYsKHRu7A-8QsAR6BAgIEAE&biw=1920&bih=969#imgrc=_
• 12mm dia neodymium magnet for module activation-1 or 2 or 3 pcs(depends on how good the ball is attracted by the magnet)
• 2.5mm dia x 20 mm screw black + nut -1pcs.
• 3mm dia x10mm SS screw + nut -1pcs.
• DC step down buck converter - output to 5V. If can be fixed or adjustable,
  I have the one adjustable.
  https://www.ebay.com/itm/5Pcs-MINI360-3A-DC-DC-Step-Down-Buck-Power-Supply-Converter-Module-MP2307-Chip/152860942585?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D20131003132420%26meid%3D1f1d9a86eea847b084315ad18b81cbed%26pid%3D100005%26rk%3D5%26rkt%3D12%26mehot%3Dag%26sd%3D172130477465%26itm%3D152860942585&_trksid=p2047675.c100005.m1851
• MOSFET transistor 2N7002 (or any N-channel mosfet).
• resistor 120 ohm-1pcs
• resistor 4.7 kohm -1pcs
• perfboard small -1pcs
• servo wire 150-200mm -1pcs
  The electronic pcs and screws you can have at home like me or buy from online stores.
  See also pictures down the page with explanations how is made.
  Price is less than 10 dollars if you count by individual parts.

Note:

• The MOSFET transistor along with resistors are soldered on the same board as the IR led (green perf board).On the buck converter I soldered on the IN pins a JST PH 2.0 connector.
  The magnetic module activation(12mm dia magnet) if installed with double side sticky tape on the x carriage in the left.
  Make sure the DIY touch me sensor is installed vertically.Use a spirit level to ensure that.
• added version 3 of touch-mi sensor.It looks better.
• Attention:The magnet from the module activator to be adjusted back enough to avoid being triggered during printing session.It will activate the probe only when homing the printer head.
• The probe will be adjusted in close position 2mm above the hot-end nozzle.You can use some 2 mm thick printed sheet for calibration.
• The probe can be used also as stand alone DIY touch -mi probe routing the wires to MKS board Z end stop connector.
• In place of the screw in can be used an 2.5 mm broken black drill bit, and sharpen the tip(pointed tip).For stopper if can be used a 3 printed or metallic washer and glued on the drill bit.

Todo:
Design a new pcb to for all electronic parts(IR-TX) and attached at the back of the sensor.

The wireless part can be adapted also to BLTouch

inductive sensor and others.

Marlin firmware changes.
//#define BLTOUCH // ANTClabs BLTouch sensor (might also work with clones)
//#define SN04 // Green sensor

define INDUCTIVE_NO // Normally open inductive sensor

//#define INDUCTIVE_NC // Normally closed inductive sensor
//#define SERVO_PROBE // Endstop switch on rotating arm. Set servo angles!
//#define NOZZLE_PROBE // Nozzle wired up to contact metal on bed

//#define TRIPOINT
//#define LINEAR

define BILINEAR

//#define UBL
//#define MANUAL

define SENSOR_LEFT 49//(use your value here )

; add in your slicer G-code
;Start G-code
;add after G28
G29
G1 Z-5.0 ;this is to retract the sensor probe(magnet) assuming the Z_HOMING_HEIGHT is 5mm
G1 Z5.0;go back

https://youtu.be/1siBJUK0WSE

https://youtu.be/zdy2BfiY3-g

Tested accuracy of the sensor.

M48 Z-Probe Repeatability Test
Finished!
Mean: -0.006800 Min: -0.010 Max: -0.003 Range: 0.008
Standard Deviation: 0.002337