Auto Bed Level Inductive Sensor for 3D Printers 

Tried your diode method on my project with 5xNPN sensors, works flawlessly! Previously I was tearing my hair out with this problem. Thanks mate, your video was a big help!

Very good video. Thank you for showing two options to connect the 12 V NPN sensor (also with the diode). For me the first option (the voltage divider) did not work, even though everything worked as it was supposed to, but my MKS BASE 1.5 board just did not see the 5V output as a high signal (tried with and without pullup resistor settings etc in Marlin). The second option however (with the diode) is way more elegant for the 12V sensor and very clean to install. Thanks for your explanation and time to make this video.. I have learned something... again! :-)

Another great video! I really love the topics of your videos. And the hypercube is really well designed.

Thank you very much for this bright and clear tutorial my friend. Thanks to your help i can continue making my 3d printer much better working in essence. And i needed this mental upgrade so much in my learning proces to produce better quality prints just right now. One can only wish receiving help of this level, this grade once stumbled upon the subject matter between those three proximity sensors. Just without choosing to go gamble. This is huge (it really is for me!!)

The diode trick is just awesome! it's simple and effective. thanks!

Excellent video with perfect explanation! Thank you very much.

dude, thank you. I got in to 3d printing to learn more about adrino and electronics explanations like this are very helpful. I ordered your pnp 5v from bang go because of you!!!

My "12v" npn nc probe is finally working! I had to adapt my array of resistors cause i'm using 13v. Now the signal pin has 5v as well. Thanks a lot!

again a great video, thanks. My HyperCube is about 70% finished, getting into the electronics part now. so this video came just in time :)

Very useful information, this helped me a lot. Thank you!

As always best of the best Full instruction and fun to watch and cute accent

Thanks very much for the explanation of how a diode works in place of a divider. I'd seen it suggested somewhere, but couldn't figure out what they were doing :)

Great video - even years on ...

Thank you so much for making this video! I've been trying to sift through low quality, not clear forum and youtube tutorials for days looking for the answer to wiring this probe. This video is fucking perfect! Thanks!!

Perfect explanations, thanks !

Nice explanation and demonstrations. Thanks.

Very informative video. Thank you.

this video is always so helpful

aaaahhhh my head is going to EXPLODE!!!.......great video

Great explanation! Thank you!

Great Video!! thanks. I tried both the Voltage divider and the diode...and in the end the divider didn't work for me, but the diode worked perfectly...and the DIode was easier.

Great video. Should be compulsory viewing for anybody starting out with ABL

If you secure a thin steel pad over each sensor to the bed, it greatly increases the sensing distance on aluminium based printing beds.

FYI, i did connect a square type inductive sensor to ramps directly without divider and it worked... for a while then i had to use different pin for probing.

Thank you. Very helpful video.

I rarely comment something... but this is awesome... tnx a lot

Very great video!

Thank you so much for that video. Your instruction was very easy to understand and you have answered a lot of my questions. I do have an NPN switch and it is Normally Open. I have decided to use the diode in reverse option to wire up my switch. Are there different types of diodes or what specs should my diode have? Also, what is the likely-hood of that diode failing and killing my board? Should I also include a fuse of some sort?

Great video, thanks

Hi folks (: I don't know if this was addressed yet, but just found out (making a printer for my friend) if you are using Marlin or other firmware with an easy option to implement inductive probing and are using glass bed, you can use 4mm distance inductive probe. Trick is that your glass should be no more then 3mm thick and you have to apply copper tape approx 20x20mm under the probing points. I tried it yesterday and it works! Hope this helps someone. ... and since copper tape is 7um i think you could easily stack two together on top to get perhaps longer distance detection, but like i said it works with single layer of tape under 3mm glass.

Just beautifull!

thank you for this ! I've seen bigger orange inductive sensors, do you know what it means ?

THANKS VERY MUCH MATE

Why don't we use capacitive sensors? With them the glass sheet would be not a problem. Now I want to upgrade my 3d printer with a proximity sensor and I don't know why don't buy LJC18A3 regard LJ18A3 type sensors.

Hi, thank you for yur video. Other than the probe, what needs to be done do put this to work?

Great video, but one question. If I have an aluminum heat bed, with a glass printing surface, will this still work, or will the glass mess up the leveling?

I wired the NPN directly to my boards Z min port and it is functioning. It is a rated 4mm sensor and i get a detection distance of 1.74mm which is just over 40% of the rated distance on an aluminium board. My tester gave me a reading of 4.7vdc on the supply pin.

Great info and presentation. Could you please tell me where I would be hooking in to my Cr10 board. Does it just use the z end switch terminal using ground and output signal? I'm new at this sorry but others may have the question.

Do you recommend or not, use the resistors?

The saturation voltage of a silicon transistor is not the same as a diode forward voltage drop. It is typically around 0.2V, not 0.6V.

Hi @Tech2C, Ive recently been getting a problem with the probe set up on my cube. I'm using the 5v pnp as you've used here from your link to banggood and ive also connected it up with your quick switching mpx connectors. What I've noticed recently is im not getting a reliable level on consecutive G29s and occasionally my readouts add 1 or 2mm to random probe points. Some people have suggested buying a different model of sensor or adding diodes somehow to the line but before i do and in the time it'll take for the parts to arrive i'd like to know if there's something i can do to fix it as clearly it works on your build without problems. I did notice a new line of text on the screen in your MPX quick connecter video mentioning a diode. Is this something im missing in my build or was that for use with a different probe set up? I really dont want to have to mess with the current MPX wiring if possible If it helps I am having issues currently on my big printer running on the ramps board, marlin 1.1.8 (i think) but I plan to move this head over to my new "stock" hypercube build that will run on the Big Tree 1.3 when Banggood send me the parts im waiting on.

I prefer the sensor that is NC as its constantly sending a signal. Because if the probe for some reason stopped functioning the satiety features of the software would detect no signal and therefore not attempt a probe. However if its NO the firmware wait for a signal, but this also means the probe could be completely unplugged.

Sorry, stupid question but I've printed out, your Bowden conversion ( great) but when I come to swop the head, my carriage is different, the four holes I have seem standard for the Prussa i3 but I think yours is none standard??? How does your x carridge attach please? I cannot seem to find a pic at the back to work it out. Thanks

Hi there, i have a LJ18A3-8-Z / BX 8mm and cannot detect the alluminum bed behind the glass build plate, not even the glass, but detects metal, any ideia?

what do you think about BL-Touch? do you have plan to insert it in your printer?

thanks for the video!! great thing!! Have you tried not using the voltage divider and connect the S directly to the S pin on the board? (ONLY the S from the sensor, so only one cable) and the sensor takes the the 12 v directly from the PSU? it would trigger the same, since it would send the negative to the S ping that is 5V + causing the same action as it would a mechanical endstop. mine is working this way without any issue.. Just thought your probably could test out for others, it would probably make life easier.... cheers

Great video, thanks once again. I'm thinking very seriously about building a hypercube, I know you have suggested some updates, but can I just ask you - if you were going to start from fresh, would you vary from your designs? Happy new year!

for your bowden drive, do you have a link to files that are for the actual drive gear? thanks!

With capacitative probes the logic is normally to keep them as close to the bed as possible (1mm above nozzle). I've heard this isn't necessary with inductive probes as their resolution doesn't depend on sensing distance. Is this true?

Is there probes with longer detection distance out there ? 1.6mm is to little if you use a glassplate of 2mm....

Thanks ❤️😊

i have proximity sensor DC 10-30 V and can i use this with break out board cnc work with 5v

@Tech2C which board you putting this on?

Please note that while some PNP probes might work on 5v, the sensing distance might be reduced when operating at less than 12 volts. I thought that those NPN sensors would have 'open collector' (or open drain) outputs,' and would operate a load connected between a positive source (5-12 volts) and the grounded output signal based on the wiring diagram. You could then connect a pull up resistor to 5V to generate a positive true signal to the RAMPs board. Certainly they show a load connected to the output between +12 and ground! If the output with no trigger is due to an internal pull up to 12 volts, (measure the resistance between the output and +12 with no power) then it should be safe to connect a 4.7 or 5.1 volt zener diode between the output and ground to clamp the voltage at a safe logic level and set the Ramps input to inverting wtih pull ups. Your method of using a series diode would work, but I might suggest a Schottky diode, which has a lower voltage drop for better S/N at the input. PNP sensors supply a 12v output signal to a load connected between the output and ground. For these you need a level converter. Connect the output signal to a 470-1000 ohm resistor in series with a 4.7 or 5.1 volt 1 W zener diode to ground. The cathode of the zener is connected to the resistor, the anode to ground. Take the output across the zener diode. The endstop input should be set to non-inverting, and pullups are disabled. In both of these cases I am assuming a "NO" type logic, IE: the output is active when triggered for positive logic. You can buy stainless steel or iron foil and apply this to the glass plate on the print bed to increase the sense distance since the sensor works better with iron based materials.

You have the resistors backwards.. 10k to ground and 15k to sense wire.

Love this video! For the PNP voltage divider setup how do we tell which pin to send the voltage of the two? Is it just as easy as throwing on a multi meter to see which is negative and connect the neg pin to the voltage divider?

Hi, so I am going to use an inductive sensor as abl sensor on my Ender 3. Is it now better to power the sensor directly with the 24 volts of the power supply and reduce the signal down to 5 volts or should I just power the sensor with 5 volts (if it works with 5V)?

can you make an picture to show me how you connect this npn sensor with resistors on the printer? i cant get it rto work :(

The capacitive sensors have the same behavior between PNP and NPN?

I am getting 5.4V on the signal wire of my sensor. Will this fry my Anet A8 board? I assume not but its high enough to make me uncomfortable about trying it without asking someone if they think its fine. I am using the 10k/15k resistor setup.

I got the PNP sensor for my hypercube but wont work it gets 4.96 volts the light shines a little bit but on 12v it works just great.. I now going to use it white the resistors.

I have a problem. I connected the inductive npn no probe, the red light turns on but it keeps slamming to the bed. I tried resistor with 12v (it should work. On 5v) anet 8.

Common types are LJ12A3-4-Z/XY，here postfix XY can be AX/AY/BX/BY means NPN NC/PNP NC/NPN NO/PNP NO, in Merlin cfg the Z_MIN_ENDSTOP_INVERTING needs to be set as false/true/true/false, respectively. Using 12V power we need 15K(serial)/10K(to ground) divider to get down to ~5V, using 5V you might need to add 10K pull up for NPN or pull down for PNP then it should work. 8/12/18 sensors stem size D15x50/D21x60/D29x68, washer dia is larger. .cfg pull up is too weak no need to use. Sensor is an oscillator, when close to metal it stops oscillating changes output.

I am just setting this up now and trying to get the resistors in place using the NPN. When I measure voltage with no metal I am getting 6.6 v, when I am close to metal I am getting .66v. As I understand it 6.6 will fry the Arduino as it is above the 5v threshold. Could it be the 10% tolerance of the resistors I sourced?

What about glass over aluminum like the cr-10 has?

TLDR: It's safe to plug a 12v source into a 5v pin on a micro **as long as there is at least 7k ohms in the line** (no resistor divider needed). Frankly one could use any resistor above 7k likely up to 500k or more without degrading performance - Personally I would likely use a 47K or 100K resistor as I have loads of those on hand. Click "read more" to understand why! Why this works: Inside the micro there are diodes on every (I/O) pin which clamp the pin voltage to within one diode drop of the ground and supply rails. These diodes aren't particularly beefy when under sustained load, they are largely intended to protect against moderate ESD or other short transients. Therefore it is perfectly safe to send far more than 5v into a pin as long as the current flowing into the pin and through the clamping diode is sufficiently limited. The datasheet on the 2650 doesn't state what these diodes can handle but 1mA sustained is likely very reasonable and conservative. Where 7k comes from: Input voltage of 12v Micro supply voltage of 5v (ignoring diode drop makes for a more conservative calculation) This leaves 7 volts (12v - 5v) which will need to be dropped across the resistor + clamp diode circuit. Using Ohms law (V = I * R) rearranged to solve for R (R = V/I) we can calculate the resistor value needed to limit the current to 1mA Gives: 7v / 1mA = 7k ohms. And there's no need to really push 1mA through this diode - the digital IO on a micro is very high impedance and really doesn't require much current flowing into it - *choosing a resistor which is much higher than 7k ohms is advised!* _At some point if you choose an extremely high resistor value (likely in the 10's to 1000's of Megaohms) the micro will begin having trouble sensing the signal so don't go too crazy as you will likely get cross talk issues far before this point._

Great vid and explanation. Noob question. How do you get into the firmware to make changes?

Hello, first of all thank you for this nice education. I am using 24V power supply in my 3D printer and want to connect Capacitive PNP NC Sensor LJC18A3-8-Z / BY. How many resistance I need to use for this. Thank you very much in advance.

I did all of instrucitons. I am using voltage divider 100k and 150k ohm resistor, I am connecting with ramps Z_min port but when i send M119 Gcode, Z_min looks always open but İnductive sensor's led is lighting.

I was trying to setup marlin for my printer, and its throwing me errors saying i need to enable either x min or x max. Ive tried disabling max, min, both, neither, and its still throwing me that error Any ideas?

I used it to speed sensor for spedometer. Is It possible in high speed over 50mph the sensor is not able read almunium? My oem speed sensor use 100mA but my proximity sensor 40mA is It effect the reading? Can I Put npn transistor to incrase the Amp? Please help..

Hey. Could you make a video how to connect LJC18A3-H-Z / BX to the SKR 1.3 disc step by step? I think fub people would be very grateful ...

great video does heat from bed not affect good working of these sensor ? (probing before heating or not ?)

im not sure what im doing wrong but i cant get the printer to use the prob for homing the Z axis when i home bot X and Y go to 0 and the printer tries to find a Z but sense they XY are both on zero they are not on top of the bed.. Please help

Should I shield the cable?

how much watts is they 2 risistor added up to

How about this model (on aliexpress): LJ18A3-8-Z/BX-5V ? It's advertised to be working at 5V, and has 8mm detection.

Hi, i have open sensor and when it detects metal diod is red but m119 taling open, not trigged. Please help. I have NPN No

Great video, but I tried the one from your link and it is not working with 5v :(

Ok I’ve pulled my ACKLP and upgraded it with a 5V NPN NO inductive sensor to the Z Min and have the sensor working. HOWEVER when it does a Auto Calibration, the inner circle of data spots senses fine, then the sensor which is -39mm in y 0mm in x goes off the bed and crashes the whole thing. What am I doing wrong?

what is the distance between the bed and sensor

My only regret is I have but one thumbs up to give

Why not just epoxy a steel washer to each sensor point thereby increasing detection distance? It's outside the build area. Just a thought.

hi, when you say min z endstop plug the yellow wire , you refer to the S+ pin right of z_min . 2nd question if i read 3.1 volts from the yellow wire and when triggered the npn 12vd feed i get 0 , is it normal or a use the wrong resistor ??? thank you for the info . can i use a 1n4001 diode for the signal.

Does anyone know what is happening with my setup? I've used an NPN induction sensor with the same voltage divider. When untriggered the voltage is about 3.36V, when triggered the voltage is 0.35 ish. When using the m119 the state of the sensor is cycling between open and triggered. Almost every time i send the m119 command, it has changed state. What the heck is wrong, and how to fix it? Any help would be much appreciated!

I had good results using a 5 volt regulator across the signal to groud

the reversed diode methode worked fine for about 20 min or so. after a while it failed for some reason and it passed the 12v to the arduino. which caused all the electronics to frie except the ramps shield. including the lcd and the arduino. juat use the voltage divider. its safer!

I was wandering if anyone could help me... I had a 12v inductive sensor working through an opto-coupler until a had a soldering iron incident that damaged the wire close to the body of the sensor... So I decided to go for a a 5v sensor to replace it (cleaner install). When I hook up the sensor and run an m119 it always says triggered (or open if I reverse the logic) and doesn't change state when a metal is out near the sensor. The red led reacts to the presence of metal but the end stop state doesn't change. I have used a multimeter to check voltages...when open the sensor passes 4.90v through the z-min signal wire, when triggered this voltage drops to 2.2v. I tried enable the pull down on the z_min in marlin and reflashed. In doing this the triggered voltage now drops to 1.6v. It's my understanding that in order change the state of the end stop marlin needs.the triggered voltage to drop below 1v. Given that I'm using a 5v sensor j thought this would be plug and play.. Can anyone offer any advice? Thanks in advance

There is another way, using a 12v relay means that the sensor can work on 12v without being actually connected to the board by any means right?✌😜

Is it possible that your voltage divider resistor values on the video are revered ? If I do the math with 10k between Output and Vout and 15k on ground to Vout, I get 7.2V whereas if I reverse the resistors, I get 4.8V ?

on pourras mete un regulateur 5V entre le Z-port et le capteur pour éviter le risque de tension de 12V emporter sur le pc

My inductive sensor has only two wires Can you help me?

je n'arrive pas a configurer mon capteur PNP sur prusia I3

hy, im having some trouble with temperature, if i got my bed more warm, the measure changes, what could it be?

Is it possible to use mesh bed leveling like the Prusa I3 with this setup?

hi bro can you please tell me that can we connect PNP NO sensor directly in anet a8 printer or we also need to do changes in farmwear please tell me in detail because i made my own 3d printer but i stuck in installing sensor please help me to resolve i will be very thankful to you ?

Have you considered trying BLTouch? I've used an inductive sensor before switching to BLTouch and haven't looked back since. One pro to BLTouch is you don't need a metal bed, and I understand bed weight may not be a big concern on a CoreXY compared to any prusa designs, but less weight is always better :)

Ordered the sensor thru your link - mks sbase card also needs 3.3 - 5V on XYZ switches. Resurrected Zonestar Prusa I3 clone is cranking out hypercube parts as I type. Parts flying into my mailbox thick and fast. Chaos reigns. Will keep you posted re Mks sbase controller card and 3.2" touchscreen. >Charlie

I just use a lm7805 in the output of the sensor and send the output of the lm7805 to the mother

amazing video :) thanks. I ll now go on and hopefully not fry my arduino xD