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  1. #1
    Can someone help me, I am using a PLCM BOB is states 12 V for the switches. I am trying to use PNP type NO 6 to 36 volt proximity sensors.
    I have determined that I need to add a resistor to the signal on the BOB.

    Can someone help me to determine the size resistor I should used and confirm that PNP types should be connected to the input signal.

    Thank you for looking

  2. #2
    I think what your saying is your bob wants a 12v high/low, but the switch is 36v? so you need to make a 12v high/low based on a 36v signal?

    Im not sure that is the actual problem, but incase it is, perhaps one of these is the kid for the gig?

    http://www.alliedelec.com/Images/Pro...S/70214711.pdf

    looks like rs sell them?

    Buy Linear Voltage Regulators Voltage Regulator; 50 W @ degC; 10 mV (Typ.); 80 mV (Typ.); 60 dB (Typ.) NTE Electronics NTE1936 online from RS for next day delivery.

  3. #3
    Quote Originally Posted by kingcreaky View Post
    I think what your saying is your bob wants a 12v high/low, but the switch is 36v? so you need to make a 12v high/low based on a 36v signal?
    I read it as the switch will run between 6V and 36V ..Clive

  4. #4
    Quote Originally Posted by Clive S View Post
    I read it as the switch will run between 6V and 36V ..Clive
    That's correct. The issue here is that the sensor output will be open collector, so it can't source current. You therefore have to add a pull-up resistor in. The value isn't critical, I expect something like 4.7k would be fine.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  5. Careful here... the switch type is PNP, BOBs are generally -ve ground, so its not a pull-up resistor but a load resistor.

    The only manual I can find online for the PLCM says inputs are 5v CMOS buffered, no indication of whether opto-isolated or not. What PLCM BOB have you got and where does it say 12v??

    Assuming the input is not opto-isolated then need two load resistors in series of 1k and 470R

    Click image for larger version. 

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  6. #6
    Quote Originally Posted by irving2008 View Post
    Careful here... the switch type is PNP, BOBs are generally -ve ground, so its not a pull-up resistor but a load resistor.

    The only manual I can find online for the PLCM says inputs are 5v CMOS buffered, no indication of whether opto-isolated or not. What PLCM BOB have you got and where does it say 12v??

    Assuming the input is not opto-isolated then need two load resistors in series of 1k and 470R

    Click image for larger version. 

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    Thanks everyone for replying, just to recap yes it is a 6 volt to 36 volt switch.

    So much conflicting advise, re use of pull up resistor.

    yes is PNP type, manual link is here http://www.zappautomation.co.uk/en/a...attachment=165

    shows 12 volt on diagram fig 4 limit switches connection.

    Am I better off getting different proximity switches if so can you recommend.
    different voltage?
    here is blurb from manual.

    Limit switches connection
    PLCM-B1 has 15 inputs for XP-26-XP40 switches connection.
    Physically each input is optocouple with built-in transition resistor
    (1 KOhm, depending on sensor type and sensor supply voltage the
    increase in resistance is probably required). This construction of
    optoisolated inputs allows to connect any sensors to module and
    provides driver optoisolation from sensors.
    Optoisolated inputs states are translated to CNC MACH3
    program and are indicated by LED14-LED28 according to fig.2.
    External LEDs connection is provided by XP41-XP55.
    Simple contact switches (buttons) and non-contact sensors
    (inductive, capacitive) of PLL01 type (inductive non-contact sensor)
    can be connected to the module. Connection is accomplished
    according to fig.2. Separate power supply unit with necessary
    voltage is strongly recommended to use for sensors supply.
    12V module supply can be used in an extreme case (in this case
    optoisolation will not be).


    plasticsales (Mark)

  7. Ok, the diagram I show is correct but omit R2 and connect the proximity switch output to INx+ and connect INx- to ground. Make the value of R1 anything between 0 (ie a direct connection) and 470R assuming a 12v supply, its not that critical. More than 12v will need higher value. You can use the 12v output from the BOB but then you get no opto-isolation. Do you have any other power supply on the machine side?

    Note the proximity switch connection shown in fig4 in the manual is for an NPN switch.
    Last edited by irving2008; 21-08-2013 at 09:10 AM. Reason: added note

  8. #8
    Quote Originally Posted by irving2008 View Post
    Ok, the diagram I show is correct but omit R2 and connect the proximity switch output to INx+ and connect INx- to ground. Make the value of R1 anything between 0 (ie a direct connection) and 470R assuming a 12v supply, its not that critical. More than 12v will need higher value. You can use the 12v output from the BOB but then you get no opto-isolation. Do you have any other power supply on the machine side?

    Note the proximity switch connection shown in fig4 in the manual is for an NPN switch.
    I am using a separate 12 volt power supply.

    Thank you for your help I will have to order 470R I have some 1/2 watt 10K and 1.5K resistors.

  9. Quote Originally Posted by plasticsales View Post
    I am using a separate 12 volt power supply.

    Thank you for your help I will have to order 470R I have some 1/2 watt 10K and 1.5K resistors.
    I'd not bother and connect the sensor direct to INx+ since it already has 1k internally on the BOB.

  10. #10
    Done that and works without resistor.
    What it does do

    Both the leds on sensor and BOB light up when the switch senses.
    Mach3 says limit reached and stops motor.
    All good

    What it does not do is show led on mach3 screen, only a quick flash and the led on the screen does not stay on, is this due to the resistor?

    I am getting 0 volt and then 12 volt when switch is activated, will a resistor reduce this voltage to 5 volt and then show in Mach3 screen?

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