NPN Inductive Proximity Sensor as an axis End Stop

RockB

Hello, I want to use a normally closed NPN prox sensor that came as part of a ball screw actuator as the end stop for the axis. Documentation says I can directly connect this to the any of the 5-pin IOs (IO_0 through IO-9). I want to use this sensor at 24V (also my V_IN). I am using Duet 3 main board.

The NPN NC sensor has 3 wires: Brown (+), Blue (-) and Black (output). Voltage between Brown and Black is 24v during normal operation and 0v when triggered.

In terms of connecting this to the 5-pin IO:
3.3v -> No Connection
io[#].in -> Brown (+) from sensor (also needs to be connected to 24v)
GND -> Black (out) from sensor
io[#].out -> No Connection
5v -> No Connection

Questions:

Is the io[#].in and GND connections right? or they have to be switched? Slightly confused since brown (+) from sensor has to be connected to 24v and io[#].in?
Where can I source 24v from the Duet 3 board? VIN (24v) and any of the OUT (OUT1 to OUT 6 with appropriate jumper position to V_FUSED) are current options

droftarts

@RockB see https://docs.duet3d.com/User_manual/Connecting_hardware/Z_probe_connecting#npn-output-normally-open-inductive-or-capacitive-sensor

24V (brown wire) and GND (blue) can be connected directly to the PSU. Signal (black) goes to the selected io[#].in (30V tolerant). As it is Normally Closed, you don’t need to invert the pin in config.

Ian

RockB

@droftarts Thanks!

Just to confirm, only one pin (io[#].in) is used out of the 5 pin IOs.

When connecting sensor (+) and GND to PSU, it should be the same PSU powering the VIN in duet right? to maintain common GND

droftarts

@RockB said in NPN Inductive Proximity Sensor as an axis End Stop:

Just to confirm, only one pin (io[#].in) is used out of the 5 pin IOs.

Yes, that's correct. You can still use the other pins on the io connector if you want/need.

When connecting sensor (+) and GND to PSU, it should be the same PSU powering the VIN in duet right? to maintain common GND

Yes, or if using a separate PSU, tie the PSU GNDs together. You could connect the sensor positive to V_FUSED from an unused heater output, or from the fan power jumper selector (if accessible) or a fan header (with fan selector on V_FUSED) assuming the probe doesn't draw much current (please check first!), which would offer a bit of protection with the fuse. You can connect GND to the ground pin on the IO connector.

Ian