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?
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
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.
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
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.
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
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?
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
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.
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?
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.