Best Capacitive Proximity Sensor for Glass Sheet on PCB Heater?

I just installed LJC18A3-H-Z/BX on my printer directly with 12v from Aux 12v of board and black to signal all is working fine with sensor about 12 mm above the glass. I originally used 15k and 10k resistors (Thomas Video) but the 3.3v from signal when not triggered to 0v when triggered is not being detected by my board (MKS gen2Z-v1.2). The LED from the sensor lights up but the Z axis does not stop moving so I tried the direct method with the higher voltage output and it works perfectly.I will try different resistor combination and see what signal voltage works with my board. Or is there a firmware config that can be adjusted?

I think you will need to change the voltage divider resistor in order to get as close to 5VDC as you can. I cant remember exactly which i used but i ended up with 4.8 volts,
Are you sure you didn't have them the wrong way round ??

When using a voltage divider the red light will be lit dimly all the time but become brighter when an object is detected . This is normal

Good luck

Even Thomas (video) had his voltage at 3.3V but it works for his board. Yes that is how mine works LED lit dimly then brighten. I will try different combinations tonight when I get home I was just reading about voltage dividers.

My LJC18A3-H-Z/BX has started to let me down. First of all I've been finding the results inconsistent. If I go to one part of the bed, home Z then manually move the probe down until my nozzle is 0.1mm above the glass I get a different result to that on another part of the bed - sometimes as much as 0.3-0.4mm which makes it hard to find a decent z-offset and leads to failed prints due to the first layer not going down properly.

Also had a couple of instances in the past week where the sensor fails to detect the bed, luckily I was watching and killed the power. I found it started working again after squeezing the probe shaft with some pliers.

I don't know whether it's just my sensor playing up or whether capacitive sensors are inherently unreliable/inconsistent. Don't know whether I should order a new sensor or look at other options like a servo/switch based probe.

Anyone else had similar problems?


(EDIT)

Have ordered a replacement capacitive sensor for now and have ordered one of these as a longer term solution although it may take a few weeks to arrive from Oz (http://aus3d.com.au/electrical/endstops/ir-z-probe). I think ultimately this will be a more reliable solution and should hopefully allow me to switch out build plates without having to adjust the z-offset.

Edited 2 time(s). Last edit at 10/28/2016 09:13AM by JBFUK.

these kind of sensors are used all day every day in industrial applications. So what are you posting in your thread ???

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bigfilsing
these kind of sensors are used all day every day in industrial applications. So what are you posting in your thread ???

Yes, but only to detect that a object is near - not where triggering at a precise distance from a target is required.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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dc42

Quote
bigfilsing
these kind of sensors are used all day every day in industrial applications. So what are you posting in your thread ???

Yes, but only to detect that a object is near - not where triggering at a precise distance from a target is required.

Absolutely but i was more wondering what the post was aiming at ?
Inductive or cap sensors have to be better than a micro switch at least i think so Haven't actually done any comparison tests.

DC42 your IR sensor works a treat ...in fact ive just ordered a second one :-)

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JBFUK
My LJC18A3-H-Z/BX has started to let me down. First of all I've been finding the results inconsistent. If I go to one part of the bed, home Z then manually move the probe down until my nozzle is 0.1mm above the glass I get a different result to that on another part of the bed - sometimes as much as 0.3-0.4mm which makes it hard to find a decent z-offset and leads to failed prints due to the first layer not going down properly.

Also had a couple of instances in the past week where the sensor fails to detect the bed, luckily I was watching and killed the power. I found it started working again after squeezing the probe shaft with some pliers.

I don't know whether it's just my sensor playing up or whether capacitive sensors are inherently unreliable/inconsistent. Don't know whether I should order a new sensor or look at other options like a servo/switch based probe.

Anyone else had similar problems?


(EDIT)

Have ordered a replacement capacitive sensor for now and have ordered one of these as a longer term solution although it may take a few weeks to arrive from Oz (http://aus3d.com.au/electrical/endstops/ir-z-probe). I think ultimately this will be a more reliable solution and should hopefully allow me to switch out build plates without having to adjust the z-offset.

I've been having the same issue. I tried switching from glass to aluminum print bed to see if the results are different. So far its better but the readings are still no consistent across the bed. Should I try replacing the sensor, or is this normal?

OK, I read this thread and I am confused on the path to go. I recently purchased a LJC18A3-H-Z/BX NPN sensor. If I wire blue to ground, brown to 12v there is about 9V coming out of black when not triggered. When triggered it drops to 0V. I see a couple of posts with different wiring options:

• Option 1: Wire BLACK -> GROUND, and BROWN -> 12V, and BLUE -> SIGNAL on the Anet Z-Stop (see madmike8's posts on page 2 of the thread)
• Option 2: WIre BLACK -> 15K RESISTOR -> SIGNAL on the Anet Z-Stop, and BROWN -> 12V, and BLUE -> GROUND, and BLUE -> 10K RESISTOR -> BLACK (per Tom's Guide) (see usen's posts on page 2 of the thread)
• Option 3: Wire BLACK -> GROUND on the Anet Z-Stop, and BROWN -> 5V on the Anet Z-Stop, and BLUE -> SIGNAL on the Anet Z-Stop. (I have seen some comments around that might work when wired to 5V via the Z-stop pins for power. I would assume that there is no issue with to high of voltage, resistors, etc. I actually tried this wired under option 2 and the sensor didn't seem to work. I am thinking of trying the wiring in Option 1 but to 5V instead of 12V.)

Is either of these the more correct way or better for some reason. Option 2 seems to be more or less how the sensor was designed to wired but involves extra steps. I'm not sure why Option 1 works at all and can't really tell if this is more of a hack way to get it to work but obviously I don't need to go find resistors or do any soldering (not a big issue except the resistors might have to wait for in the mail).

Thoughts and suggestions would be appreciated...I was hoping setting this up would be just follow some instructions posted somewhere but there seems to be more on the inductive sensors and less on this capacitive sensor..not to mention there doesn't seem to be a clear path on hwo to wire it.

Thank you

EDIT: I did play around with this a bit. When wired like option 2 but no resistors I get 2.92V on the signal wire so no voltage issue. I also found out the sensor is actually working but can't detect the bed and/or metal for some reason. If I put my finger right on the end of the sensor and touch it, the sensor light will go on and the sensor will trigger. But I literally need to touch the sensor. I tried playing with the little screw on top of the sensor which I thought was for adjusting the sensitivity, but no change from doing this.

Edited 6 time(s). Last edit at 02/04/2017 11:14AM by heatvent.

Hi
The issue is that the sensor needs 12 volts in order to function BUT the 12 volts ( or in your case 9 volts that comes out of the signal wire is too much for the control board and will probably damage it.
Inductive or capacitive just follow the wiring colour code as per the sensor spec ( either spec sheet or marked on the sensor itself)

So we use a voltage divider ( 2 resistors) which is a common simple way of lowering a voltage to a level that the control board can accept.
Just look at Toms video and the schematic he draws. The signal wire is connected to one end of the 15K resistor. The other end of the 15K is connected to one end of the 10K & a new wire which will become your new sensor wire ( with the lowered signal voltage) the remaining other end of the 10K goes to ground.

Thanks for the reply. I will likely go this route. Out of curiosity, the guy who develops the skynet software for the Anet A8 seems to sell these same sensors but wired to connect directly to the z-stop connector (listing on ebay...[www.ebay.ie]). Any idea how he is able to achieve this? I realize the sensor is rated a 6-36V and the 5V is low, but I thought that it just brought down the range. However, since the sensor is rated up to 8mm you still got enough range (say 2mm) to use at 5V. Maybe there are variations in the quality of these. Would be neater of course to just hook straight up to the existing JST connector on the board if that could be done. But maybe more reliable using the method above?

Also, not sure if you have see the write at [3dprint.wiki]:


Normally the following color code is used for the sensor Harness :

Black - Signal - for NPN it is 0V=active, high impedance OR supply voltage for inactive
Brown - Power supply - See sensor for the Voltage*
Blue - Ground - 0V
As most sensors need a voltage larger than the 5V provided by the connector there are two options:

Purchase a pre made board:
1. OctoCoupler
2. For 5V sensors or for some 6-36V sensors use the 5V supply of the connector. Anet and Skynet uses this option for their sensor and it works for the LJ18A3-8-Z/BX. According to some users the low voltage acceptable for the “ornage” sensors. But the this might lead to unreliable readings as it is not designed for this voltage.
3. If you have an open collector NPN sensor (see above) than you may connect the brown wire to the the 12V input of your board and the blue to the ground and finally the black wire to the Z switch (the board should have an internal pull up).
4. If you have an sensor with an internal pull up resistor(see above) than you may connect the Brown wire to the the 12V input of your board and the blue to the ground. There are the following options:
a. Than add a resistor between the black(signal) and the blue(ground) wire to reduce the resulting voltage from 12V to 5V. The best way is to test it with different resistors and measure the voltage between the signal(black) and ground (blue). Best to start with is 10k, for me it worked with 5k. Increase the resistance if the voltage is to low, decrease if it is to high. When you found the correct resistor you can connect the signal pin (black) to the signal pin of the z-probe plug as shown on the picture.
b. The disadvantage of using resistors is that it depends on the power supply voltage and a change of this voltage my damage your printer. This can be avoided by using diodes see here. Method nr. 3 is the recommended one, just be careful with the polarity of the diode.
5. Some tutorials recommend to use two resistors. But this is only for PNP-sensors and for high-active inputs. In our case this would lead to errors. When the sensor switches to 0V and the Atmega internal pull up is activated there would be about 2,5V on the signal pin which is not recognized as low by the AVR.

UPDATE: I tried wiring the sensor directly to 12V with the signal pin disconnected to see if I get better range on the sensor. While the LED light does seem brighter when triggered, I still need to literally touch the sensor head in order to get it to trigger. Any idea if I have a bad sensor and/or if there is a sensitivity adjustment?

Edited 3 time(s). Last edit at 02/04/2017 11:49AM by heatvent.

BLTouch can also be an option. It doesn't matter if you print on glass or metal.....

Hi
You don't need to copy and paste all that information every time.

6 to 36 VDC is the operating voltage that the sensor needs to function The voltage you supply it can in some cases effect the sensors sensitivity ( which in turn effects its sensing distance) Normally on FDM printers we only have 12 or 5 VDC and as 5 VDC is lower than the minimum 6VDC it forces us to use 12VDC to power the sensor.
Most FDM control boards use endstops that have a 5 volt signal level to indicate if they are triggered or not. Often internal pull up / pull down resistors hold the signal until the microswitch is activated Offering a higher level voltage will damage the boards inputs, hence the use of resistors
as a voltage divider . Works fine.
The only thing i can think of is that ( at least on my sensor) the indicator LED on the sensor is always on dimly when not triggered and goes bright when triggered. This has to do with the internal wiring of the sensor and there's not much to do about it. Mine has been working fine like this
for over 2 years now. So im confident its not something you need to worry about. It also doubles as a visual aid that your sensor is powered up so its not a bad thing


Good luck

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heatvent
UPDATE: I tried wiring the sensor directly to 12V with the signal pin disconnected to see if I get better range on the sensor. While the LED light does seem brighter when triggered, I still need to literally touch the sensor head in order to get it to trigger. Any idea if I have a bad sensor and/or if there is a sensitivity adjustment?

Normally there's a small adjustment screw near the LED indicator

Thanks for the reply. FYI no dim light for me it's just off and on when triggered. Can you give me an idea how the sensitivity adjustment screw works. I turned it about 11 times and it doesn't seem to stop anywhere and also doesn't seem to affect the sensitivity. There are no indicators on the top to show how this should work. For example turning right is more sensitive or less sensitive… Not sure. Any advice would be appreciated.

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heatvent
Thanks for the reply. FYI no dim light for me it's just off and on when triggered. Can you give me an idea how the sensitivity adjustment screw works. I turned it about 11 times and it doesn't seem to stop anywhere and also doesn't seem to affect the sensitivity. There are no indicators on the top to show how this should work. For example turning right is more sensitive or less sensitive… Not sure. Any advice would be appreciated.

Its been so long since i set mine up i can t remember but i seem to recall it was quite sensitive. 11 turns sounds way too much. I guess you will just have to experiment.
Keep in mind you only want the sensor to trigger +/- 1 mm higher than the hot end. ( you then fine tune with the Z off set in your firmware.
Good luck

So here is where I landed...


I have the orange version of the LJ18A3-8-Z/BX sensor. The 5V seems to power it just fine wiring black to signal, brown to 5V power, and blue to ground. When signal is tripped I get about 3V on signal which is about perfect.

Mine needed to be adjusted for sensitivity and apparently turning the POT screw on the top of the sensor counterclockwise increases the sensitivity and turning clockwise decreases it. I had to turn the screw a good 11 times or so to get it to trigger at about 2mm.

The light on mine is normally off when not in a triggered state, then starts blinking rapidly when first triggered and turns solid when it gets closer to the bed.

I am going to stay with this setup and see how things go. If I get inconsistent results I may try wiring at 12V but this is much cleaner than setting up that way. Thanks for the help and hope this helps someone else.

Edited 1 time(s). Last edit at 02/04/2017 07:50PM by heatvent.

Hey everyone,
I am looking forward to install a NPN NO capacitive sensor to autolevel a delta.
But I need help regarding the bed surface. It doesn't sense a transparent glass but it does sense a mirror glass from a fair distance. The sensitivity is 10 mm.
Will it sense a transparent glass plate that has been painted black on one side ?

Hi guys I used to battle with these sensors which are not really purpose made for 3d printing and get frustrated with them.

There is a better way....
[forums.reprap.org]
[www.thingiverse.com]

We've designed these to do exactly what 3d printers need.

---

Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

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VJain
Hey everyone,
I am looking forward to install a NPN NO capacitive sensor to autolevel a delta.
But I need help regarding the bed surface. It doesn't sense a transparent glass but it does sense a mirror glass from a fair distance. The sensitivity is 10 mm.
Will it sense a transparent glass plate that has been painted black on one side ?

Capacitive sensors are the least good option. See [www.youtube.com].

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42

Quote
VJain
Hey everyone,
I am looking forward to install a NPN NO capacitive sensor to autolevel a delta.
But I need help regarding the bed surface. It doesn't sense a transparent glass but it does sense a mirror glass from a fair distance. The sensitivity is 10 mm.
Will it sense a transparent glass plate that has been painted black on one side ?

Capacitive sensors are the least good option. See [www.youtube.com].

Wiki covering most of the various options [reprap.org]

Piezoelectric disc sensors are well liked by all who have tried them, proving accurate, robust and cheap.

Mike

This explains it all really:

[www.youtube.com]

I ditched my capacitive sensor as had two of them fail, I suspect due to heat. Now using an Aus3D IR sensor but not completely happy with the way it responds to glass. Now thinking about a BLTouch sensor.

Hi just wanted to add my experiences with NPN since there's a lot of mixed messages about it.

If it's NPN you don't need any resistors, just plug the black wire directly in to signal even if probe is running on 12V. I did a lot of googling about this and could'nt find any definitive answer to this but in the end I just went for it and it worked. I was reading 11.5V when sensor wasn't triggered and wire wasn't attached, but after I attached the signal wire to the input it was showing 5.3V so it's working flawlessly now. Probably some internal resistance in the pin input, I have no idea, but I'm glad it worked.

I have been using capacitive sensors in my printers for the last 2 years without any issues, mine are connected to 12 volts power supply and a single lm7805 on the output signal to the board just in case.

Yes they might need little adjustment depending on the bed temperature but I already have set the different offsets in my S3D processes.