NPN Inductive Sensor



  • Hi Guys,
    I have connected a diode to the sensor, with anode side(no line on the plastic) into the connectors on the duet wifi, and the cathode side(line on the plastic) into the wire on the sensor itself.

    LJ12A3-4-Z/AX

    When using either E0 STP pin or the Z STP for the sensor signal no light comes on. i.e. when the probe is triggered the red light is turned off, when the probe isn't triggered the red light is on( in my case the lights have never been on to begin with)

    Please Help as this is making me pull my hair out.
    At the moment the sensor is connected to the E0 Connector
    The code is as follows:

    ; Endstops
    M574 X1 Y1 S1;
    M574 E0 Z1 S0;
    M558 P4 X0 Y0 Z1 E0 H10 I1 F80 T6000 ; for inductive sensor, Set Z probe type to switch, the axes for which it is used and the dive height + speeds
    M557 X0:170 Y13:180 S25; Define mesh grid
    G31 P1000 X0 Y0 Z0; Set Z probe trigger
    alt text


  • administrators

    1. If you are using a glass bed, are you sure that the sensor can detect the aluminium below it?

    2. Otherwise, it sounds like a wiring issue to me. You haven't shown where you have connected the sensor power and ground wires.



  • Its a standard inductive sensor where the light turns of when it reaches the bed, whilst the red light near the motor connector(when connected to the Z STP) doesn't light up at all i.e. regardless of whether the sensor is triggered or not. The VCC(power) is connected directly to the power supply, this is where the red light is at its brightest.

    Ground is connected to any ground pin as expected.

    Either the board is faulty or the cable i ran through the cabling and there is no issues im actually gonna test it

    PS How comes theres no IRC chat, Ive been working on this all day especially with the z probe issue, that method of chat would be great. Kind Regards, How comes reprap has issues with the bed leveling in 2018, marlin seems to be easier on that aspect, But I paid a lot of money to have the comfort of the duet.


  • administrators

    In your photo, which wires go to the Duet - the green ones at the bottom, or the black/blue ones at the top - and which to the sensor?



  • the side with black goes into the duet


  • administrators

    Then the wiring looks OK. if you have a multimeter, please measure the voltage on each side of the diode, relative to ground, when the sensor is triggered and when it is not triggered.

    PS when you said:

    When using either E0 STP pin or the Z STP for the sensor signal no light comes on. i.e. when the probe is triggered the red light is turned off, when the probe isn't triggered the red light is on( in my case the lights have never been on to begin with)

    which red light did you mean: the one on the sensor or the endstop LED on the Duet?



  • Hi,
    I'm referring to an endstop led.
    Thanks
    what would you mean relative to ground.

    Would a voltage divider make it easier. For this kind of probe.


  • administrators

    @npm1 said in NPN Inductive Sensor:

    Hi,
    I'm referring to an endstop led.
    Thanks
    what would you mean relative to ground.

    Would a voltage divider make it easier. For this kind of probe.

    No, for an NPN output sensor, use a diode. Some people have found that it needs to be a Schottky diode, e.g. BAT43 or BAT85. It depends on your sensor.



  • @dc42
    i used all three diodes on three different cables no differance and not working at all, this was the case on when this was connected in probe connector


  • administrators

    @npm1 said in NPN Inductive Sensor:

    Its a standard inductive sensor where the light turns of when it reaches the bed, whilst the red light near the motor connector(when connected to the Z STP) doesn't light up at all i.e. regardless of whether the sensor is triggered or not. The VCC(power) is connected directly to the power supply, this is where the red light is at its brightest.

    Does the red endstop LED turn on if you disconnect the VCC to the inductive sensor and connect the output wire (which is connected to the diode cathode) to ground? If it doesn't, then the diode is faulty or not connected correctly.



  • @dc42 now that is really interesting
    ill give that a go and take from there


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