PNP Inductive Sensor and wiring

ajcraig99

@dc42 based on my wonky wiring and feeding 24v into the 3.3v connection, is it likely to be repairable or is the board dead do you think?

ajcraig99

Can someone please confirm if the below wiring diagram is correct before I fry another board?

dc42

@ajcraig99 said in PNP Inductive Sensor and wiring:

@dc42 based on my wonky wiring and feeding 24v into the 3.3v connection, is it likely to be repairable or is the board dead do you think?

I'm sorry to say that it's almost certainly dead.

Your wiring diagram looks OK, but personally I'd connect the blue sensor wire to the GND pin of the always-on fan connector instead of the Z probe connector, so that in the unlikely event that you get a short inside the sensor, the current will be restricted to the fan circuit. The ground side of the 10K resistor can still connect to the ground pin of the Z probe connector if you find that more convenient.

ajcraig99

The above wiring didn't work, I took the sensor to work and had one of the electrical guys test it and it only changes about 0.3v when triggered so It seems to be a dud sensor.

I picked up an NPN sensor and tested it on the bench with a 9v battery and it goes from 0v to virtually -7v when triggered so have tried to use this one.
Unfortunately I am still unable to get this one working and I can't work out what I am doing wrong.
It seems to work perfectly (judging by the LED and voltage measurements) until the probe output is connected to z_probe_in or ground, then it just stays triggered.

Sensor: LJ12A3-4-Z/BX

It was listed as normally open.

I have tried to illustrate what I've tried below.

sigxcpu

Your NPN sensor is most likely open collector. That means you need a pull-up resistor to V+ from its output. Then, to protect the Duet add a diode when connecting the signal wire.

https://mertarauh.com/2017/01/18/dont-trust-the-internet-and-how-to-add-an-inductive-proximity-sensor-to-your-3d-printer-the-proper-and-easiest-way/

ajcraig99

@sigxcpu

Thanks,

So I read through that page and measured the resistance between each wire.
results in the image below, If I use the 10k value as R1, should I be wiring it up like the bottom diagram?

dc42

See the wiki page on connecting Z probes. You don't normally need the pull-up resistor.

ajcraig99

@dc42

I have read the wiki countless times. I should be able to plug it straight in with a reversed diode on the signal wire for protection.
I don't know why sigxcpu suggest I install a pull-up resistor, I don't know what an open collector is but I have read through the link he/she posted and am still none the wiser but am willing to try anything.

I have the new NPN sensor wired up currently as per the wiki and my image below.

With the Z_PROBE_IN disconnected, The LED is on when not sensing and turns off when near a metallic object. Indicating I have a NC sensor.
with the Z_PROBE_IN connected, The LED is on regardless of it sensing or not, It dims very slightly when near a metallic object. The duet does not sense a change when using M558 P1 or P4

sigxcpu

Maybe @dc42 says that pull-up is not required because Duet already has one. Basically, you connect brown (+) to V+ (do more than 5V because those senors like more), blue (-) to GND just like in your schematics. The black (output) wire is connected through a diode (put the line of the diode towards your sensor).

When the sensor is not activated the signal line of the Duet stays at Duet's 3V3 because of the internal pull-up. When sensor is triggered, the last NPN transistor shorts the signal (its collector) to ground (its emitter).

In theory, no diode will be required, but if the sensor has also an internal pull-up (not open collector) it will push its V+ with higher voltage towards Duet's signal and nasty things can happen.

Measure the voltage on Duet's signal pin when triggered and not triggered in your last schematic. Untriggered should be ~3.3V and triggered should be ~0V.

ajcraig99

Update:

I spent way to long thinking I was more stupid than I am trying to get this to work.
Ordered another sensor, exact same model number and it works perfectly. I think I might be using the wrong diode though because it reads 715 when triggered instead of 1000 but it still seams to work so I'm happy.

Thanks for everybodys patience.

Jeremy Watkins

Not to hijack the thread, but I am also trying to wire an inductive sensor on my older Duet Wifi (I think I am version 1.01). My dilemma is my sensor is a PNP NO DC6-36V, but my fans are 5v fans (can't easily switch them either because I am using a specialized 20mm centrifugal fan due to size constraints on my effector). So I am pretty sure that rules out connecting to the always on fan connections. I have found an abundance of cheaper 5V DC NPN sensors on Amazon which would fit my physical setup, but I am not sure if I would need to use a different diode than a BAT43 or BAT85. The sensor I am considering is a LJ12A3-4-Z/BX-5V.

dc42

@jeremy-watkins, if using a 5V NPN sensor then you don't need the diode.

Jeremy Watkins

@dc42 Thanks, I'll give that a try then! Brown to V-FAN with the jumper on 5v, blue to GND, and black to Z PROBE IN. No voltage divider needed either?