BOB and NPN Proxy Switch wiring question.


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Thread: BOB and NPN Proxy Switch wiring question.

  1. #1
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    Default BOB and NPN Proxy Switch wiring question.

    I'm using LJ12A3-4-Z/BX NPN 3 wire Proxy Switches for my new Avid CNC 4848.
    The Proxy Switch signal wire (on 12v source) puts out 12v constant and when triggered drops to 0.68v,

    My BOB has 4 external inputs (estop,limits etc) that set at 5v (high) so I assume I need to ground these when the limit switch is triggered.

    How do I get the proxy switch to ground the 5v and how do I protect the BOB from the 12v input when it's not triggered?

    TIA

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    Default Re: BOB and NPN Proxy Switch wiring question.

    if the LJ12A3-4-Z/BX NPN 3 wire Proxy Switches output switches between 12V & 0.68V

    they are not open collector NPN outputs as I would of expected

    and must have a pullup resistance between the output & the +12V supply

    ( do the switches have a LED indicator between the + supply and output ? )


    details of the machines BOB would help

    I would try using a Schottky Diode to connect the Proxy Switches output to the BOB input

    by connecting the cathode (with the band ) to the switch output and the anode to the BOB input

    the forward voltdrop of a Schottky Diode is about 150–450 mV. ( instead of 600–700 mV, for a silicon diode )

    this will pull the BOB input closer to ground for a valid logic 0 but block current flowing from the +12V and into the BOB input


    example wire ended Schottky Diode

    STMicroelectronics 70V 15mA, Schottky Diode, 2-Pin DO-35 1N5711

    RS Stock No. 168-6622

    https://uk.rs-online.com/web/p/produ...YAmQ&gclsrc=ds



    I'm assuming the BOB input is either a 74 series TTL input or Cmos input with a pull down resistor to ground

    john



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    Default Re: BOB and NPN Proxy Switch wiring question.

    Switches I'm using:
    https://www.ebay.com/itm/5Pcs-LJ12A3...72.m2749.l2649
    The have a typical LED that lights up when metal is detected, not sure if it's between the 12v+ and Output wire.

    The BOB seem great but is hard to find anything in depth on, best info I have is here.
    https://www.instructables.com/id/6-A...terface-Break/
    https://www.amazon.com/gp/product/B07PSJF5HN

    BOB IC:
    74HC14

    Got the Diods in my shopping cart, suggestions for pull up resistor/s for 19v source for Proxy switch power?

    Thanks John

    Last edited by dbtoutfit; 08-29-2019 at 10:58 PM.


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    Default Re: BOB and NPN Proxy Switch wiring question.

    You could use a relay board like this and from the contacts of the relays, just apply ground to the board input when it's active. https://www.ebay.com/itm/4-Channel-1...53.m2749.l2649



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    Default Re: BOB and NPN Proxy Switch wiring question.

    looking at the picture of the BOB

    the inputs have opto-isolators its possible the resistors that limits the LED current when the input is grounded
    are connected to a +12V supply and thats what you measured when the switch is off

    BOB and NPN Proxy Switch wiring question.-fr0fvkxiljwrfpw-large-jpg

    the resistor may be about 1K (1000 ohms) which would limit the LED current to about 10mA when the BOB input is grounded



    If I am correct
    seeing more that 5V at the BOB input terminal is not a problem even though the 74HC14 IC is powered by a 5V supply

    possible opto -isolator used ? PC817
    data sheet

    pc817 datasheet.pdf

    John

    Last edited by john-100; 08-30-2019 at 06:41 AM. Reason: correct typo


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    Default

    At the moment I am using my 12v lab PSU for testing the proxy switches wired only/directly. BOB is installed on the machine and has not be tested along with.

    Each input pin: has 5v power, has a resistor with 511 on it (think I measured .540ohms across each one) and they are all protected with an opto then to another resistor on the back side.

    I didn't think I needed a resistor for the proxy switches because it was active high and then goes low when the switch is flagged. I was thinking a resistor for reducing the voltage on the output/signal (black) wire to protect the BOB. Which if your correct would be great to not need.

    NOTE:
    I have read these Proxy switches will actually function off 5v. (i will give this a try today) Would that make things simplier?

    Beside the high level of input signal (12v), theoretically - when the proxy switch is flagged and drops to O.68v would that pull the active high 5v input pin/s to ground or 0V triggering a 0 or false to mach3?

    I have attached a close up of the BOB with the Optos in view.

    Always appreciative of the help.
    Eric

    Attached Thumbnails Attached Thumbnails BOB and NPN Proxy Switch wiring question.-0829191349-jpg  


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    Default Re: BOB and NPN Proxy Switch wiring question.

    OK

    so the LJ12A3-4-Z/BX NPN 3 wire Proxy Switches output switches between the 12V supply and 0.68V without a connection to the BOB

    on the breakout board
    the opto-isolator is just another manufacturers version of the PC817 from panasonic I expected
    the resistor on the board that limits the LED current is 510 ohms ( marked 511)


    what voltage do you measure between the BOB's input opto isolator pin 1 and the limit switch common / ground ?
    BOB and NPN Proxy Switch wiring question.-0829191349-jpg

    if the opto-isolator pin 1 was at +12V
    you can connect the BOB's input to a Proxy Switches output run from 12V

    if the opto-isolator pin 1 was at +12V
    and you connected a Proxy Switch connected to a 24V supply

    I would add a diode to stop the BOB's input being pulled higher than 12V that would result in the LED being reverse biased

    John



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    Default Re: BOB and NPN Proxy Switch wiring question.

    I have 5v at pin1 using the Input common ground.

    I also tested the Proxy Switch from the BOB Input 5v & Common GND and it does trigger from about the exact same distance as when on 12v.
    In this case as you might guess the Proxy switch is 5v until flagged in which then it drops to 0.61v.

    Thoughts?

    TIA
    Eric

    Attached Thumbnails Attached Thumbnails BOB and NPN Proxy Switch wiring question.-lj12a3_4_z_bx-data-sheet-jpg  
    Last edited by dbtoutfit; 08-30-2019 at 11:34 AM.


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    Default Re: BOB and NPN Proxy Switch wiring question.

    that internal diagram of the LJ12A3-4-Z/BX NPN 3 wire Proxy Switch explains a lot

    and confirms there is a pullup resistor to the switches positive supply

    this is what I had before you posted the details
    BOB and NPN Proxy Switch wiring question.-proximity-switch-bob-jpg


    so you either can power the Proxy Switch from 5V
    or add the diode to protect the BOB input from being taken over +5V
    ( the reverse brake down voltage is only a few volts and depends on the LED colour)

    in the case of the EL817 opto isolator the maximum reverse voltage is 6V


    John



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    Default Re: BOB and NPN Proxy Switch wiring question.

    I don't have your electrical wits but looking your your top diag, do you see any reason I can not just wire Brown+ to +5v Input, Blue- to Input common GND and Signal wire to one of the Input pins (active high +5v)?

    If I just wire it straight forward will the Proximity switch pull BoBs Input Pin/s +5v to ground and give me a valid logic of 0 for Mach3?

    Eric



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    Default Re: BOB and NPN Proxy Switch wiring question.

    yes

    if the Proximity switch works when connected to a 5V supply ( instead of 6 to 24V )
    then connecting the brown wire to the BOBs +5V
    Blue- to Input common GND and Black Signal wire to the BOB Input
    outwill work

    found this on line indicating it has a NPN Normally Open output
    BOB and NPN Proxy Switch wiring question.-lj12a3-4-z-datasheet-jpg

    which makes it acive low

    John



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    Default Re: BOB and NPN Proxy Switch wiring question.

    Do I just wire my Estop to limit common ground and to the 5v high input pin?

    Thanks John, you're a life saver.

    Eric

    Last edited by dbtoutfit; 08-30-2019 at 12:56 PM.


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BOB and NPN Proxy Switch wiring question.

BOB and NPN Proxy Switch wiring question.

BOB and NPN Proxy Switch wiring question.