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LJ12A3-4-Z-BX wiring

Posted by jimmyclarke 
LJ12A3-4-Z-BX wiring
July 17, 2015 10:50AM
Hi Everyone,

Sorry to ask this as I know there are other posts, but I just want to (triple) check this before subjecting my printer to torture!

I ordered the orange tipped LJ12A3-4-Z-BY but received the blue tipped LJ12A3-4-Z-BX instead, and the seller is refusing to admit fault.
So before I push the return issue further, I wanted to see how I could use it.

Are any resistors needed, or will this work simply by connecting it like has been posted here before?


Thanks for the hand holding! All responses appreciated.
Re: LJ12A3-4-Z-BX wiring
July 20, 2015 09:19AM
That is correct for the typical sensor wiring colors. No resistors are needed as your sensor is a NPN and you are sinking the voltage coming FROM the microcontroller, not sourcing it going TO the microcontroller.

Instead of the 12V coming from the brown pin, you can try to use the 5V supplied with the pin beneath the blue pin making for tidier wiring. Some sensors will work with 5V even though it's below the rated spec. But if that doesn't work, what you have should definitely work.
Re: LJ12A3-4-Z-BX wiring
July 29, 2015 10:08AM
hello
Is this configuration the same for the sensor LJC18A3-H-Z/BX 1-10mm NPN NO DC 6-36V 300mA
[www.ebay.it]
I need also to put resistors like following image??


Edited 3 time(s). Last edit at 07/29/2015 10:10AM by mdcompositi.
Re: LJ12A3-4-Z-BX wiring
July 29, 2015 01:53PM
For ANY NPN sensor resistors are not needed. A NPN resistor acts like a switch grounding the microcontroller's pin. It's already at a safe voltage since it's coming FROM the microcontroller.

If it was a PNP sensor, the sensor would be sending whatever voltage it was operating at TO the microcontroller, so you'd have the possibility of sending more than 5V to the microcontroller, likely frying the pin if not more in the process. With a PNP sensor, you must use a voltage divider to lower the voltage if the sensor operates at greater than 12V.

For the above reasons, a NPN NC sensor is best choice IMHO, with a NPN NO sensor a second option but you lose the fail safe operation.
Re: LJ12A3-4-Z-BX wiring
July 30, 2015 03:04AM
Quote
cdru
For ANY NPN sensor resistors are not needed. A NPN resistor acts like a switch grounding the microcontroller's pin. It's already at a safe voltage since it's coming FROM the microcontroller.

If it was a PNP sensor, the sensor would be sending whatever voltage it was operating at TO the microcontroller, so you'd have the possibility of sending more than 5V to the microcontroller, likely frying the pin if not more in the process. With a PNP sensor, you must use a voltage divider to lower the voltage if the sensor operates at greater than 12V.

For the above reasons, a NPN NC sensor is best choice IMHO, with a NPN NO sensor a second option but you lose the fail safe operation.
Many thanks for your early reply!!
I've installed the sensor with blue and black on zmin and the brown on 12v on Ramps
and please, what are firmware modifications to do on marlin??
can I use this video or you suggest me a link or other?
[www.youtube.com]

Edited 2 time(s). Last edit at 07/30/2015 03:20AM by mdcompositi.
Re: LJ12A3-4-Z-BX wiring
July 30, 2015 08:25AM
I'd just start in the auto bed leveing section of the firmware (your firmware version/branch may have it at a different location) and just start filling in the parameters or going with default. You need to choose whether you're doing a auto grid leveling or 3 defined points. 3 points define a plane so if your bed is perfectly flat, but not level, that's the minimum best option. If your bed is not flat and is wavy to different degrees across both X and Y, a multi point 3x3 grid may average out the diffences across the bed better than just a 3-point grid. So either specify the exact cordinates of the 3 points, or the bounding box the grid will be generated from. You'll also need to specify what the offset of the probe is from the extruder. There's a few additional options for speed, and raising before and between probes.
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