Capacitive NPN sensor

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Hey, my fellow Freaks! Today I would like to bother some (or all) of you with a question that might seem simple to the hardenend embedded veteran but has proven to be extremely troublesome for me. I am trying to connect a capacitive NPN NO sensor to a microcontroller and, so far atleast, failing horribly. The controller and sensor I am using are an Atmega644PA-PU and LJC18A3-Z/BX respectively (wiring diagram for the sensor can be found as an attachement). Output voltage from the circuit provided is a whopping 12V, and I think you can see the problem with that.

Anyway if any of you guys could help me with this pesky little problem, I would be amazingly grateful!

Thank you in advance!

PlagueDoctor

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It helps if you post the image in your message - so that people can actually see it - instead of just attaching it out of view:

 

 

So what, exactly, have you tried

 

In what way(s) has it failed "horribly" ?

 

Aren't these things pretty commonplace? What research have you done to see how others use them?

 

Have you got a proper datasheet?

 

Have you contacted the manufacturer and/or supplier for application support?

Last Edited: Wed. May 20, 2015 - 11:30 AM
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This wasn't supposed to be posted here, I am new to the forum-life, sorry.

Last Edited: Wed. May 20, 2015 - 12:10 PM
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Hey, Awneil and thank you for your quick reply! The datasheet provided is of little help because a) it only has the attached image and dimensions of the sensor and b) it's in Chinese. I might have exagerated a little bit when I said that my attempts failed horribly, but I haven't been succesful so far. My main problem is that since the load has to be between the + and the black wire, there's a constant 12V there. If I would try to expand the circuit with  voltage dividers or voltage regulators for instance, those would have to be connected to ground and thus make the sensor operate incorrectly (LED that indicates detection burning constantly. Short circuit or simply wrong wiring?). If you could propose a working, and above all SAFE circuit, I would be very grateful!

Grtz

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One of the key decisions in component selection is that it has adequate support - datasheets, application notes, FAE contact, etc - for your requirements.

 

None of this comes cheap - which is why you get little or none of it with cheap stuff (Chinese or otherwise).

So cheap stuff is great when you're experienced and know what you're doing - but should be avoided otherwise.

 

Can you really not find a well-documented product with the level of support you require?

 

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No your load doesn't need to connect to 12V. The sensor is NPN that implies there is a npn transistor between the blue and black wire. You only need a pullup resistor to 5V on the black wire.

I googled 'prox npn arduino'
Should be heaps of info.

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Anyone know what NPN means? He doesnt mean silicon transistors like PNP and NPN does he? And the adjective 'capacitive' must mean something? Like you need to measure capacitance by using an ac signal?

 

Imagecraft compiler user

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Googling similar devices...

 

http://i.stack.imgur.com/kFCfj.png

 

that shows the "equivalent circuit". Hopefully it's obvious where the NPN versus PNP figures in that? Clearly it is talking about types of transistor construction.

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bobgardner wrote:
the adjective 'capacitive' must mean something?

The device is a "Proximity Detector";  it does its proximity detection by capacitive means - as opposed to an "Inductive Proximity Detector", or an "Optical Proximity Detector" or whatever.

 

eg,

 

Inductive Proximity Sensors: http://uk.rs-online.com/web/c/au...

 

Capacitive Proximity Sensors: http://uk.rs-online.com/web/c/au...

 

 

 

As Cliff says, I guess the "NPN/PNP" effectively indicates whether it is active-low or active-high - it might be historical; they might not use actual NPN or PNP bipolar transistors these days...

Last Edited: Wed. May 20, 2015 - 01:30 PM
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Thanks man, you're a saint! I did a lot of research for a correct circuit, but never tried the keyword you suggested. Anyhow, the issue hereby is solved, thanks to you and all the other helpful forummembers!

Grtz

PlagueDoctor

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The NPN or PNP refer to the type of semiconductor used in the inner workings of the device. Also I am not really qualified to explain the workin principles of a capacitive sensor to you in the most inderstandable manner possible, if you are interested I'd suggest you Google the term, I bet you'll find someone smart enough explaining it to you in the clearest way possible!

Hope it helps

Grtz

PlagueDoctor

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With prox sensors you have the 3 wire type (which we've covered) and the two wire type.
The two wire are loop powered and change the current that flows through them to switch - usually a relay. With these ones you need to read the specs carefully - they require a minimum voltage drop across them and a minimum current needs to flow to power the electronics. So, if you've got 12V, using a 12V relay may not work as you drop 4-6V across the device. Many people get trapped by that.

Just thought i'd round out the discussion on industrial prox sensors.

Last Edited: Wed. May 20, 2015 - 10:52 PM
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I've been working as a PLC Technician in several industries. NPN and PNP ouput found in industrial sensors simply mean N(-output)  P(+common)  N(-output) for NPN Type or 

P(+output)  N(-common)  P(+output) for PNP Type.         

 

Here is the Schematic Diagram:

 

 

 

 

 

Operaions on NPN

 

When the sensor is in Idle (not detects object or not active), the WHITE (OUTPUT) wire will have a NEGATIVE Voltage Output depending on the supply voltage you're using. But, when the sensor detects an object or active, the BLACK (OUTPUT) wire will have a NEGATIVE Output Voltage and the WHITE (OUTPUT) will no longer have an output and vise versa. P is just a common terminal to complete the circuit of the load which is usually a relay as shown in diagram.

 

 

Operaions on PNP

 

Same as NPN, only the OUTPUT Voltage on (WHITE) wire and (BLACK) wire changes to POSITIVE.

 

 

Hope this could help :)

 

 

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