Inductive Proximity Switch as limit switch for CNC - connection and selection of pull down resistor

Inductive NPN Proximity Switches are easy to use as limit switch for hobby CNC machines. In this video I explain how I use them and how to select a pull down resistor that fit a digital input switching between zero and ca. 5V.
If you have a limited number of inputs you may want to use two switches in parallel e.g. for front and back on the same axis. In this case you must use a resistor of approx half.
In the video I try to find resistors resulting in an output of ca 5V. The following was found: Single Sw 12V 10k; 24V 3.3k; 36V 2.2k. Two Sw in parallel: 12V 4.7k; 24V 1.5k and 36V 1k
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[@mattjoy]

Thank you for explaining this, saved my day. My machine is all wired up with the same brand of Sensors.

[@cncmachine3751]

Thanks Martin, this is very usefull for my cnc project. 👍🏼

[@georgejaxxin4957]

Thanks for this, I'm not up to speed with this, however, after messing around for 3 days then I watched this and bingo , even worked out who BoB is

[@ricstarred7993]

Many Thanks-this is great info

[@skorkmaz]

Great video. Thanks.

[@warlockd]

I thought of this and its a great idea for a cnc. My only problem is that alot of these sensors eat like 300ma. Having 3 brings it up to 900ma of power. Compare that to an optical sensor and eh. I don't know though. I really like the idea of using them instead of other sensors.

[@CLGPerformance]

I would put a voltage divider differently so the switching transistor wouldnt load up with current and heat up or damage the control board. One resistor off the end of the black wire and at the end of that resistor add another resistor and connect that to the ground. Saves the switching transistor from loading up in current and keeps the sensor from getting damaged as well as the control board |GND| | ---|sensor out (BLK)|---------|R|--------------|R|---------|Home Switch Control board|

[@johnward5890]

Could you hook up two proximity switches in series so each was getting 6 volts from the 12 volt power supply and then use the 6 volts for the breakout board?

[@steveu235]

If my breakout board is rated 12-24v on the end of the board where i am connecting the black signal wire then should i put a resistor or just leave it?

[@charleshaerle8498]

Nice Video. Can you do a video on connecting pnp nc switches in SERIES. My plc has limited inputs and it would be awesome to just use 1 input pin. Everybody shows just one sensor or they wire them in parallel. I have 4 wire pnp no/nc sensors. I want to send 5 volts through until one of the sensors sense metal and then open the circuit to ground.

[@rok1475]

Rockwell Automation published a diagram of how to connect NPN and PNP sensors in series and in parallel. In parallel connection a diode is installed between each sensor and the load. Breakout boards that have built-in pull up resistors will only work with current sinking (NPN) sensors.

[@martinbarfoed5040]

Thanks for your comment.

[@kephranet]

If you connect a 5 volt zener diode from your output to ground, you will not need a different resistor for each supply voltage. Put your resistor in series between your sensor output and the zener. This clamps the out voltage at the resistor/zener junction to 5 volts.

[@martinbarfoed5040]

Thanks for the comment. I may add this option to a future video.,. I'm also preparing one where I use opto couplers to separate the voltages.

[@jwerry58]

With a NPN sensor wouldn't you connect the resister between the Black wire and +Volts? Your diagram shows it connected to -Volts and that would be correct for a PNP sensor.

[@tracksntreadslou]

Great Video Martin..I am in the process of changing my chinese CNC router over to using Mach 3 and a ESS smoothstepper with a C25 BOB .I Need to change the NPN NO proximity voltage from 24 volt to 5 volt ..When using different 24v supplys with a different amperage is it possible that the value of the resistor needed will change as well? ..How many amperes are you testing with your unit?

[@martinbarfoed5040]

I would not expect that a different amperage of the PSU will influence the resistor you need to use. But for safety - do a test using a voltmeter before connecting to you BOB.

[@franktrapani4804]

very good explanation but can you tell me how to wire it to run a digital tachometer to check rpm of machine spindle thank you

[@martinbarfoed5040]

I havent tried that. Some controllers have a separate input for encoders to control. One I know is Acorn from Centroids

[@kampsmwila4258]

am trying to find a sensor that gives different analog signal outputs when it detects different types of metals at the same distance..need it for a coin counting system.that should be able to count different denominations of coins depending on the type of metal.your quick response will highly be appreciated.

[@martinbarfoed5040]

I do not know any sw that will do that. I hope you can find help somewhere. Good luck

[@gasparigi]

Hello Martin, nice educative video. Thanks. The output is digital or analog? Digital, for example 12V or 0V? Or it can be analog any value between 0-12V detecting distance too? I am trying to detect if target is moved from some fixed position.

[@martinbarfoed5040]

This type of switches are digital. Either on or off. Not sure what sort of sensor that will do what your are looking for. Ultrasonic maybe?

[@ikecobey6268]

Nice video if ever I used 12 volts and I need to pull down in 5 volt what value of resistor I need to get 5 volts

[@martinbarfoed5040]

Ike Cobey It must be around 10k. See video at ca 4:40

[@airgunningyup]

i think ill go with 1k ohm , need to step from 9v ( 9.2 ) to about 6v, and 10k might drop me well below 5..thank you soo much.

[@tstvideo1]

Nicely explained. I have a single axis machine ( X axis) I want to connect inductive proximity switches NPN type( LJ12A3-4-Z/BX) at the ends as limit switches. i am using Arduino Uno & a stepper motor. Where & how do I hook up the switches? Your help will be appreciated.

[@martinbarfoed5040]

You will need to connect the sw to some power - typically > 6V. The signal connects to one of the digital inputs on Arduino via a pull down resistor. I think you can use same procedure as Im doing the this video to find one that fit as you will also need ca 5V on the input

[@nielsenminibio]

Hej Martin. Tusind tak for gennemgangen. Er der en måde at regne sig frem til et resultat, da en af mine venners CNC kører på 20V?

[@martinbarfoed5040]

It's unfortunately difficult to calculate as we do not have data on the internal components in the switch. So that why I use the experimental method. If you would like to see how to calculate you may look here: www.ti.com/lit/an/slva485/slva485.pdf A guess for you 20V PSU would be to around 4k

[@anneliedstrom2890]

do you connect the ground from the PSU to the breakoutboard to?

[@martinbarfoed5040]

Yes, I did

[@thechriskelly12]

are they normally closed ones and switch to open when the metal object within the sensing distance was thinking of getting some normally open ones and using them to switch a transistor or mosfet for my grbl shield.

[@martinbarfoed5040]

Normally Closes (NC) switches will be active when no metal is near - this means that the LED is lit and you get signal out (GND for NPN and Vcc for PNP)Same story for Normally Open (NO). They will become active when metal is coming close enoygh to trigger resulting in signal out (GND for NPN and Vcc for PNP). I'm working on a video comparing all four types of switches.

[@jwerry58]

@@martinbarfoed5040 Here you say 'Normally Closes (NC) switches will be active when no metal is near - this means that the LED is lit and you get signal out' but in your other video (NPN & PNP NO NC Proximity Switches - experiments with function and Pull Down Resistors) you show the NPN NC as INACTIVE LED ON and ACTIVE LED OFF. So Which is it?

[@floydgilbertjr3545]

Hi Merry Christmas question I'm using 6 NPN NO proximity sensors and a 12 volt power supply 1 for X axis, 1 for Z axis, and 4 for Y axis 1 ea for Y- and Y+ and 2 Y Slaved When installing to my Break Out Board I have only 5 Inputs on the Board due I put 4 together for theY Axis on 1 input?

[@martinbarfoed5040]

Sorry for the late reply! I hope you found a solution. You can put the sensors in parallel - no problem. I have e.g. the Y+ and Y- in parallel sharing only one input. Same for X

[@cnc_workbench]

Hi Martin, does this work to use 24v proximity sensors with Pokeys57CNC board for limits and homing? a 3Kohm for 1 sensor and 1.5Kohm for 2?

[@martinbarfoed5040]

Hi Neil, PoKeys input are for 5v only - so you need pull down resistor or Zeener diode to use w 24v signal. Check the output with voltmeter before connecting to the controller

[@balajithirumalai1007]

which proximity sensor are you using? .i need it please respond me ASAP.can u suggest me a binary output providing proximity sensor

[@martinbarfoed5040]

Im using NPN NO. Maybe you can use this video kzbin.info/www/bejne/hWLOgJuVpNWNsKM

[@PURGE-3000]

You don’t need resistor if you switch a relay or 24V contactor to power a motor.

[@urgamecshk]

How bad is it to only supply them 5-6V from the start?

[@martinbarfoed5040]

Julius Jahn They are typically rated for 6-36V. But it seems that there is some loss of accuracy if you are in the lower end.

[@Jono6671]

most sensors I've come across are rated for 10-30v DC, so you would have to drop the voltage or interface them some other way

[@derbemoges2119]

Continuous glow of light problem what is the problem please tell me

[@martinbarfoed5040]

If you connect only plus and GND and you have the LED light up the switch is most likely broken

[@AdaptingCamera]

Why are you doing this with a resistor? You should use a Zener diode and a small resistor. That could give you 5.1V or 4.7 volt out if that's what you want.

[@MyName1979]

Where is the CNC?

[@martinbarfoed5040]

In another video :-)

[@dronesvisionsaeriennes]

Good evening Martin, excellent video, I understand how to play on the output voltage .... but I do not understand why when I place my sensor with the orange nose down, the earth, it lights up so detect, I also have the impression that it detects my hand that I approach on the aluminum body ..... but nothing happens when I approach the iron or other material ... on the orange nose ...? ?? it is connected to a control card according to the following diagram ... Black for signal, Blue for GnD, Brown for + 12V ... Here is the link of my sensor ... fr.aliexpress.com/item/32748267115.html?spm=a2g0s.9042311.0.0.27426c37ggjUer Thanks for your help... Philippe

[@martinbarfoed5040]

Are you sure what type of sensor it is? To me it sounds like it could be a capacitive sensor. The one I'm working with in thes video is Inductive.

[@dronesvisionsaeriennes]

@@martinbarfoed5040 yes, it's this following.... fr.aliexpress.com/item/32748267115.html?spm=a2g0s.9042311.0.0.27426c37wRntRd but i don't understand where the issue is...do i need to wire it with another way...? thank's a lot