BOB and NPN Proxy Switch wiring question.

[dbtoutfit]

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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[john-100]

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

[dbtoutfit]

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

[kenrbass]

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

[john-100]

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



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

[dbtoutfit]

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

[john-100]

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 ?


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

[dbtoutfit]

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

[john-100]

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



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

[dbtoutfit]

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

[john-100]

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


which makes it acive low

John

[dbtoutfit]

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

[coherent]

I had issues with NPN proximity switches also. Might have simply been the make/model or specs of mine, but between pull down resistors required etc was just a hassle. As another posted above I used a simple multi channel relay board. It was very easy to hook up and has worked flawlessly.

[john-100]

Hi Eric

I missed post 12

yes
just connect the E-Stop between the input common and the input pin (15 ?)

I would use the N/C terminals and set the switch as active high

that way a broken wire triggers an E-Stop

John

[dbtoutfit]

Will do.

If I understand correctly, the Proximity switch setup I am going with will be fail safe in the same way since its active high correct?

[john-100]

Going by the info I found and attached to post 11

the Proximity switches are normally open (N/O)
( the limit switch needs to be set as active low )

So they would fail to work if a wire went open circuit
which is very often what happens when wires are repeatable flexed



John

[dbtoutfit]

Is this why...
The Limit switch always provides 5v until it is flagged.
So If the wire breaks (because the BoB already provides a high 5v) there is nothing to bring the input to 0v so there is no logic signal sent?
But if the board didn't supply 5v and had to get it from the PSwitch sginal wire - then if the wire broke it would drop the voltage, signalling a logical machine stop?

There's not an alternative way to wire the PSwitch without involving relays, such as polarity swapping BoB hack or something right?

[john-100]

yes
looking at the internal circuit of the Proxy Switch from an earlier post ( #8 )



the 10K resistor pulls the output up to the +5V supply when the switch is open

once tripped, the switch closes and grounds the output
( the NPN transistor switches on and the output goes down to 0.68V )

John

[dbtoutfit]

Appreciate all your help John.

Only my Z Proximity switch wiring moves via wire chain the other axis wiring are statically installed.
I am hopeful this will greatly reduce the chance of wire break. I still rather have a NC setup.

Eric

[Gallen66]

Just curious,

Are you using a motion controller with this? I thought cncrouterparts included electronics with their routers.