PNP Inductive Sensor and wiring

ajcraig99

I've done a few searches but am still not too sure how to wire up and connect my LJ12A3-4-Z/BY 6-36v inductive probe as a replacement for the piezo I was using.

From the wiki:

PNP output normally-open inductive or capacitive sensor
Duet 2 Maestro, or revision 1.04 or later of Duet WiFi or Duet Ethernet: you can connect the output of the sensor
directly to the IN pin of the Z probe connector. You must also connect a pulldown resistor between IN and GND of
the Z probe connector. 10Kohms is a suitable value.

Can I simply do the below without damaging the Duet? I am running the Duet on 24v btw

ajcraig99

well shit.

that was a $300 mistake.

ajcraig99

I'm an idiot and in hindsight have very clearly sent 24v to the Z PROBE_IN and fried my Duet, I should have waiting for some input on this post but wanted to get it working before heading to the airport so was inpatient.

I think this part of the wiki could use more detail to hopefully prevent ID10T errors like this in the future

Hopefully someone can chime in with the correct wiring diagram by the time my new board arrives?

Stephen6309

I use a relay module and using the relay output, it works like a switch.

The one I used: https://www.amazon.com/gp/product/B00MMW0XWY with a buck convertor to get 12v from 24v. There are 24v ones on there also.

ajcraig99

I have a spare buck converter that I could probably use, would the below work?

fcwilt

@ajcraig99

It seems unlikely a buck converter would work due to slow response time but that is just an educated guess.

What is the voltage swing on the output of the sensor?

You may be able to use a simple voltage divider made from a couple of resistors or maybe a resistor and 2 or 3 diodes.

Frederick

ajcraig99

I see, I have no idea about the voltage swing, will have to look into that when I'm back home next week.

It sounds like a relay is going to be the easiest option right?

fcwilt

@ajcraig99 said in PNP Inductive Sensor and wiring:

I see, I have no idea about the voltage swing, will have to look into that when I'm back home next week.

It sounds like a relay is going to be the easiest option right?

Well a relay may introduce some additional error since it is a mechanical device that is not going to respond instantly.

If I were doing it I would try a voltage divider.

Once you know the voltage swing of the sensor it will be easy to determine if a voltage divider will work and what parts you would need.

Let us know what you find out about the sensor.

Frederick

Stephen6309

@fcwilt A 3D printer doesn't move fast enough for the slight delay of engergizing a relay to affect the z probing or homing. I haven't had any problems.

fcwilt

@stephen6309 said in PNP Inductive Sensor and wiring:

@fcwilt A 3D printer doesn't move fast enough for the slight delay of engergizing a relay to affect the z probing or homing. I haven't had any problems.

What was your reference probing device which you compared to the device that used the relay?

Thanks.

Frederick

Stephen6309

@fcwilt I used to use dc42's ir sensor. Changed to a proximity sensor to see if the bed was really bumpy. The bumpiness smoothed out a bit, so the BuildTak on the 1/4" MIC6 appears to be unevenly transparent to ir.

dc42

Sorry it's taken a while to reply. In your wiring diagram, you have the brown and black wires swapped. The brown wire is the power feed to the sensor, so it should be connected to V_FAN. The black wire is the output from the sensor, so it should be connected to the 10K pulldown and the Z probe input.

Also I suggest you connect the blue wire to the ground pin of the always-on fan connector instead of the ground pin of the Z probe connector, because the fan connector is designed to take more current.

What damage is evident on the Duet? I'm surprised that it has failed, other than perhaps blowing the fan fuse. The sensor may be toast though. Are you certain that you don't have another wiring issue as well?

dc42

I just spotted another problem. You are using the wrong wiring diagram - the one for "Prototype V2" instead of the one for production boards. The prototype V2 had the Z probe connector pins in the reverse order. So you fed +24V into the +3.3V pin instead of into the Z probe IN pin.

ajcraig99

@dc42

Hey no worries, I've been away anyway.

Thanks for the heads up re the sensor wire.

regarding damage, all the leds on the board are now lit and the hotend and heated bed start heating up as soon as it gets power. no wifi or usb connection works.

Are you able to link to the correct wiring diagram?

dc42

It's the big wiring diagram at https://duet3d.dozuki.com/Wiki/Duet_Wiring_Diagrams.

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/