Bed level sensors

  • Posted In: 3D printer support

  • Participant

    Hi,i`m pretty new to 3d printing & i need your collective help with my problem.
    i own a hictop 3dp17 prusa i3 clone that came with a inductive sensor, I replaced that with a proximity sensor LJC 18AC-H-Z/BX both the inductive & proximity sensors are rated 6-36v both are NPN & rated at 300mA, my board is i think a MKS MPX 3 that has a dedicated socket for the inductive sensor but when i connected the proximity sensor to the same socket nothing worked.I then connected the brown & blue wires directly to the 24v terminals & black wire to z-end stop & it worked, but the red LED is lit always on when i connect the black wire to the z-end stop but increases in brightness as it nears the print bed.

    This is not ideal as i would rather have the LED light only when it detects the bed so i can adjust the sensor screw to calibrate as needed. Do i have the sensor hooked up the wrong way or do i need to edit marlin.

    I apologize for waffling on but i wanted to give as much information as possible.

    I look forward to any help/suggestions you may have.

    Thanks in advance.

  • Keymaster

    There is the right and the easier way to do it.

    First of all, if you have not used a voltage divider, shut your printer down immediately and dont use it until you install.
    The voltage divider will reduce the 12v/24v coming from the sensor to 5V (logic) level used by the board,
    you can search it online, there are thousands of calculators!.

    Second: about it being on all the time. there are two logics kinds, PNP or NPN, i like the NPN better, because i dont need to invert the logic in the firmware, but its simple to invert. you need access to the firmware, open the configuration.h page, and change the line:
    ….”Z_MAX_ENDSTOP_INVERTING = false; // set to true to invert the logic of the endstop”….
    to true. it should work!

    Remember to activate the autoleveling function properly!, otherwise it wont work too.
    there is a guide here on how to do it, but its for servo+endstop.

    i’ll make one about inductive soon,

    • Participant

      Hi, Thanks for the quick reply.
      in your reply you say NPN sensors, the proximity sensor i have is NPN, also i have read on reprap forums & others that the sensor has worked on there boards, more so with MKS boards because they can handle higher voltages.

      In my post i mention that my MKS board has a dedicated JST socket that the inductive sensor used for its power & signal.

      This is where i am getting confused, both sensors are rated 6-36v & 300mA yet one works but the other don`t.

      Do you have any idea why that is.

      Thanks in advance

  • Participant

    LED increases in brightness – change sensor. He dead. Beside it must be sharp hysteresis.

  • Participant

    They are all proximity. You mean you are switching over from inductive to capacitive sensor? Those are adjustable, i.e. the 6-36v kind, there is a little tiny screw on top that will adjust sensitivity.

    I have not seen an installation yet where the LED is not on all the time, and then gets brighter as it gets closer, hence ‘proximity’. that is just how they work. The LED on when supplied with power lets you know that it is working.

    Italo is correct, there are several ways to wire them. Not all will require resistors, it depends on your sensor and on your board. But research first, not after you plug things into it. A fried board sucks.

    Loads of information here, read all the pages and figure out which board/sensor combo you are dealing with to figure out how to wire it.,547498

    • Participant

      Great post. I love tea (green and black) but never considered drinking it during game time. I live where its super hot so lots of water has always been the order. But I’l start trying this out soon. I’m curious to see how well Snapple would work. I know its one of the few pre made teas without high fructose corn syrup and other such ingredients. I would also recommend coconut water from time to time. It can be good for post workouts and also hangover prevention.

  • Participant

    Thank you all for your reply`s, i will check out the forum you linked.

    Thanks again.

  • Participant


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