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Can I connect a NPN inductive home switch direct to my BOB or do I need a relay?

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01 Jul 2019 19:23 #138329 by tom-rock
Hi all,

I just set up my lathe configuration with Linuxcnc.
I use the stepconf wizard with the very common cheap china 5 axis breakout board.

Can I connect a NPN inductive home switch with GND direct to the IN ports (10-15) on the BOB or do I need a relay?

The GND of the IN ports is not connected to the other GND pins on the BOB.

So I think I have to use the GND of the IN ports and +5V of the BB for the inductive proximity switch and connect the output to
an IN port (10-15).
When the switch changes to closed the IN port will be pulled to GND and Linuxcnc will recognize the homing.

Or am I wrong and will need a relay to pull the IN port to GND?

I would be very happy if someone could answer my question.

Greetings and best thanks for reading

Ralf

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02 Jul 2019 07:12 #138382 by pl7i92
YOU need a RELAY
and yoiu can connect all REF / Limit to one PIN

wirering is
12-24V to A1 of the Relay
A2 from the Relay to the BLACK cable of the NPN (LJ12A3 BX)
the Broun cable of the NPN is 12-24V
the blue one goes to Gnd


COM RELAY goes to BOB left side GND
NO of the Relay is P10-P15

PLEASE REMEMBER THAT THIS BOB NEEDS TO BE CONNECTED to 12-24V on the RIGHT SIDE to get the INPUTS tp work
SEE my YT channel


and

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02 Jul 2019 22:43 #138448 by andypugh

tom-rock wrote: Can I connect a NPN inductive home switch with GND direct to the IN ports (10-15) on the BOB or do I need a relay?


An NPN proximity switch is equivalent to a switch-to-gnd.

If shorting the BoB inputs to GND causes a change in state in LinuxCNC then you can wire the Prox directly.
Note that most prox switches do not work at 5V, they need at least 7V. You can safely use 12V to _power_ the prox because it behaves like a switch.

In one of my machines I have prox switches powered by 24V switching 3.3V io pins.

But double-check your wiring, clearly this can go wrong.

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