Endstop help



  • Im using a LJ12A3-4-Z/BX inductive sensor for my z max endstop. I have it wired to an always on fan pin, and the signal thru a diode to the z endstop connector. It lights up when triggered and the light by the z axis driver lights up as well. Theres no change when m119 is sent.

    Am I missing something? I've tried setting m574 z2 s1 and s0 but there is no change when the sensor is triggered.


  • administrators

    What type of diode are you using? Others have found that an ordinary silicon diode doesn't pull the endstop pin low enough and you need to use a Schottky diode.



  • I am using "FAIRCHILD SEMICONDUCTOR 1N4148TA DIODE, ULTRAFAST RECOVERY, 300mA, 100V, DO-204AH"
    I beleive I bought this based off info here but it was a long time ago. I read somewhere else last night to hook sensor ground and signal to the endstop pins. I currently have ground and power hooked to an always on fan channel. Could this be it?



  • I'm using a LJ12A3-4-Z/BY (PNP with a diode similar to yours), on my printer:
    ; Endstops
    M574 X1 Y1 S0 ; Set active low endstops
    M574 Z1 S0 ; Set endstops controlled by probe
    M558 P3 H5 F120 T6000 ; Set Z probe type to modulated and the dive height + speeds
    G31 P250 X16 Y30 Z0.5 ; Set Z probe trigger value, offset and trigger height


  • administrators

    @rs4race:

    I am using "FAIRCHILD SEMICONDUCTOR 1N4148TA DIODE, ULTRAFAST RECOVERY, 300mA, 100V, DO-204AH"
    I beleive I bought this based off info here but it was a long time ago. I read somewhere else last night to hook sensor ground and signal to the endstop pins. I currently have ground and power hooked to an always on fan channel. Could this be it?

    Try a Schottky diode instead as recommended at https://duet3d.com/wiki/Connecting_a_Z_probe#NPN_output_normally-open_inductive_or_capacitive_sensor.



  • Thanks again! The Schottky diode works.

    To sum things up. The 1N4148TA diode didnt work.
    I Wired the LJ12A3-4-Z/BX inductive sensor as follows:
    Power wires to always on fan channel (24V)
    Blue is Ground
    Brown is 24V

    Signal wire to Z stop pin of Z stop Connector
    Black - (Cathode) Schottky Diode - Z stop pin

    In config I set

    M574 Z2 S0 ; z axis homes in positive direction active low

    And my Z home file

    G91 ; Relative positioning
    G1 Z200 F420 S1 ; Move quickly to endstop
    G1 Z-2 ; Back off of endstop
    G1 Z3 F60 S1 ; Move slowly to endstop
    G92 Z186.5 ; Set Z axis position
    G90 ; Absolute positioning

    I hope this will help anyone with the same question.


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