1. #1
    Hi,
    I would need some help please with wiring correctly the proximity switches/LJ12A3-4-Z/BX Inductive Proximity Sensor Switch NPN DC6-36V/ to C23 board.

    Now i read carefully all posts about that and thought that i understand it, but maybe i am making some basic mistake.





    What i would like to achieve is all axis to have 2 switches at both ends each , one as a limit and one as a home. All limits in one pin, all homes at one pin and A home/ second long axis gantry motor/ separately, so be able to square the gantry by adjusting the switches.





    I read carefully the manual of the board with the wiring diagrams, but maybe i am missing something.


    First the manual of the board says: "Note. The bellow wiring diagrams require setting the inputs to use pull-down resistor."


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    Second the manual shows how to measure the internal resistance:

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    So i calculate its 11kOhm, so say roughly 10kOhm


    These switches are supposed to be normally open. They have 3 wires brow blue black.

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    I supply them with 18VDC + at brown -at blue. There is 18v at black, measured between black and blue. I activate the switch with metal object and black goes to 0v.


    I followed the corresponding diagram and what i read here at the forum, so wired them like this:
    All blue together , all brown together. all black limits together, all black homes together + one black home separate for the long axis squaring.

    Now the diagram says connect negative/blue/ to board ground.
    I treat 18v as 24v so i connect 10kohm resistor between the input pin and corresponding wire.


    So now inputs light but they can not detect triggering of switch. Whatever i change in mach3. I even changed the inputs of the board to high/what i read here on the forum/ but still nothing happens.

    One by one the switches work but connected together nothing happens. I searched the web but could not find something better, they all refer C23 diagram in fact.


    I am ignorant in electronics, but still wonder how this works, as when more than 1 switch blacks are connected there is always same voltage in the black measured to ground, how the board will detect something happens?

    What am i missing here?
    Last edited by Boyan Silyavski; 09-07-2014 at 05:33 PM.

  2. #2
    An NPN sensor means the output is an NPN transistor which is wired as a switch to ground, if it was a PNP it would be a switch to the voltage rail.
    So what you have is a resistor pull up which will show volts until you turn on the NPN when it will show ground.
    But you don't want volts, you want current so you have to add resistors to get the current down to something that doesn't blow the LED in the BOB.
    Ohms law sez R=V/I
    V is the voltage guess 24V less 1.5V for the LED, 22.5 V
    I is the Amps, guess 15mA for the LED, 0.015 A
    R = 22.5/0.015 = 1500R = 1k5
    10k sounds like way too much.
    Where's Irving when you need him?

  3. The Following User Says Thank You to Robin Hewitt For This Useful Post:


  4. #3
    Silyavski, I'm having similar issues, maybe my basic explanation will help if my problem can cast a common light on the issues?

    I have 2 NPN proximity switches, each a 3 wire switch.

    I set up a simple bench test with a 12v PSU and connected proximity switch brown to +ve and proximity blue to -ve then I used a simple continuity tester across the proximity black and brown.
    As the proximity senses a metal target, the continuity test works as I would expect.

    Then I set up Mach and the inputs so that I can see the BOB inputs are working on the Mach diagnostics screen.

    Also the proximity switches light up with thier little LED, they work with a continuity test.

    BUT when I connect a -24ve to the proximity switch and the Bob on one pin, and the poximity black to the other Bob pin, nothing happens in Mach.

    Any ideas?

  5. #4
    > all black limits together, all black homes together
    > i connect 10kohm resistor between the input pin and corresponding wire.

    Try adding a separate resistor to each black lead, then linking the free ends of the resistors to the input pin.

    Adrian.

  6. #5
    Quote Originally Posted by Saracen View Post
    > all black limits together, all black homes together
    > i connect 10kohm resistor between the input pin and corresponding wire.

    Try adding a separate resistor to each black lead, then linking the free ends of the resistors to the input pin.

    Adrian.
    Tried this to no avail. Sensors will not work this way.

    Quote Originally Posted by TonyD View Post
    Silyavski, I'm having similar issues, maybe my basic explanation will help if my problem can cast a common light on the issues?

    I have 2 NPN proximity switches, each a 3 wire switch.

    I set up a simple bench test with a 12v PSU and connected proximity switch brown to +ve and proximity blue to -ve then I used a simple continuity tester across the proximity black and brown.
    As the proximity senses a metal target, the continuity test works as I would expect.

    Then I set up Mach and the inputs so that I can see the BOB inputs are working on the Mach diagnostics screen.

    Also the proximity switches light up with thier little LED, they work with a continuity test.

    BUT when I connect a -24ve to the proximity switch and the Bob on one pin, and the poximity black to the other Bob pin, nothing happens in Mach.

    Any ideas?
    At the end i solved the problem after checking with the board maker. He assured me the diagrams are correct and that only one 10k resistor is needed per input/when 24v/

    So i started doubting all else. Measured cabling, connections, all seemed right. Then very frustrated as a last attempt i changed all cabling with new /20AWG/ and it works now.
    i believe the under rated /China/ thin cable was playing me tricks. F****g Chinese cables and connections. Never again.


    So basically Tony, this is the way to connect them properly / NPN Normaly Open proximity sensors,24V to 5v input./ as described in my first post
    The setup with my particular board is the following:
    Pull Down inputs on the board and Active Low ticked in green in Mach3/ my board permits to pull up or down the inputs via shorting combination of 3 pins/

    Did you check your setup with 2 or 3 sensors directly wired together and directly to the board and 24v, without any connectors and cables in between? + the respective resistors i mean?

    This pdf is for my board but it seems everything concerning connecting different types of proximity switches is quite well explained.
    Last edited by Boyan Silyavski; 10-07-2014 at 04:46 PM.

  7. #6
    Clive S's Avatar
    Lives in Marple   Stockport, United Kingdom. Last Activity: 12 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 5-6 years. Has a total post count of 2,309. Received thanks 403 times, giving thanks to others 35 times. Made a monetary donation to the upkeep of the community. Is a beta tester for Machinists Network features.
    Some sensors have internal pull up resistors built in hence the calculation to determine it. In my case that value was 10K so no external resistor is required.

    Your PDF explains that very well. saying R1 + R2 needs to be 10K if R1 (internal) is 10K then R2 (external) is not needed.

    Hope this helps. ..Clive
    Last edited by Clive S; 10-07-2014 at 05:15 PM.

  8. #7
    Thanks Folks.
    Silyavski, in the end I didnt need resistors, as Clive says it may be because the Proximity switch has a resitor in it. Like you, I ended up wiring the Proximity sensor much closer to the BOB and it worked! :) I then traced and rewired the connections and the junction box and I'm good now. Just need to mount the proximity switches onto the frame, adjust and then see how I get on with dual homing in Mach. Thanks again.

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