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LJ12A3-2-Z/BX onto RADDS 1.6 Board?

Posted by unf0rg0tt3n 
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unf0rg0tt3n
LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 04, 2019 04:53AM
Hi all,

I have a question about connecting the inductive sensor (12V) to my RADDS board.
Every forum, has other messages because the situation is really different.
people also often use RAMPS instead of the RADDS board.

when connecting the inductive sensor to my board is it possible for me to wire it:

Sensor--------Board
12vdc -------- 12vdc PSU / or board
GND -------- GND PSU / or board
SGN -------- ENDstop Z-min signal pin

Or do I need to make a voltage divider of some kind

Thanks in common,

Dennis
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Dust
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 04, 2019 05:15AM
At its heart its just a ramps but for the Arduino Due.

You need some way to drop the signal from 12v to 3.3v max. (Since the Arduino Due has 3.3v logic)

A voltage divisor will work, but make sure you turn off the pull up resistor of your probe pin in firmware.

use 3.6 kΩ and 9.1 kΩ for 12v to 3.1 volt
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unf0rg0tt3n
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 04, 2019 06:01AM
Quote
Dust
but make sure you turn off the pull up resistor of your probe pin in firmware.
What happens if I don't do this step?

Quote
Dust
use 3.6 kΩ and 9.1 kΩ for 12v to 3.1 volt
I don't have these resistors I only have 10K and 3.3K and these:
0 , 1.5 , 4.7 , 10 , 47, 100 , 220 , 330 , 470 , 680, 1k , 2.2k , 3.3k , 4.7k , 10k, 22k , 47k , 100k , 330k , 1M (ohm)

But with 10K and 3.3K I get 2.977 volt will that be enough or does it need to be closer?
because I can mix up 10K and 3.3k + 100 that will be 3.1 as well.
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Dust
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 04, 2019 06:26AM
"What happens if I don't do this step?"

The pull up resistance becomes part of the voltage divider ( Arduino Due, it is between 50kΩ and 150kΩ. in parallel from signal to vcc) and the output voltage is wrong. (higher than wanted, worst case 3.4v enough to damage a 3.3v IO line)

"But with 10K and 3.3K I get 2.977 volt will that be enough or does it need to be closer?"

should be fine, anything over 2v should be accepted as a high.
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unf0rg0tt3n
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 04, 2019 07:12AM
Quote
Dust
"What happens if I don't do this step?"

The pull up resistance becomes part of the voltage divider ( Arduino Due, it is between 50kΩ and 150kΩ. in parallel from signal to vcc) and the output voltage is wrong. (higher than wanted, worst case 3.4v enough to damage a 3.3v IO line)

"But with 10K and 3.3K I get 2.977 volt will that be enough or does it need to be closer?"

should be fine, anything over 2v should be accepted as a high.

Good to hear!
So when still enabling pullup it fries my stuff sad smiley

About the FW; I want it to correct for minor inconsistencies in the bed level. so I need to set the signal pin on Z_Min signal?
Which would be configured as:

#define ENDSTOP_PULLUP_Z_MIN false
#define ENDSTOP_Z_MIN_INVERTING true
#define MIN_HARDWARE_ENDSTOP_Z true

I'm using repetier btw
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MMcLure
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 04, 2019 02:57PM
Another possibility is to just use a reverse-biased schottky diode like a 1N5817 instead of a divider network. Connect the cathode (striped end) of the diode to the signal wire from the sensor, and the other end of the diode to the microcontroller pin, and turn ENDSTOP_PULLUP_Z_MIN on. When the sensor is not sensing anything, the diode will block the voltage and the pullup will pull the signal pin high, when the sensor triggers it will pull the signal pin low through the diode. No need to calculate resistor values for a divider.
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unf0rg0tt3n
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 04, 2019 03:43PM
Quote
MMcLure
Another possibility is to just use a reverse-biased schottky diode like a 1N5817 instead of a divider network. Connect the cathode (striped end) of the diode to the signal wire from the sensor, and the other end of the diode to the microcontroller pin, and turn ENDSTOP_PULLUP_Z_MIN on. When the sensor is not sensing anything, the diode will block the voltage and the pullup will pull the signal pin high, when the sensor triggers it will pull the signal pin low through the diode. No need to calculate resistor values for a divider.
Thanks for the tip about the 1N5817!
What microcontroller pin do you mean, because by "ENDSTOP_PULLUP_Z_MIN" I think you mean the endstop Z_min?
I't still on smiling smiley I have my mechanical end stop still connected.
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MMcLure
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 04, 2019 04:53PM
Quote
unf0rg0tt3n
Thanks for the tip about the 1N5817!
What microcontroller pin do you mean, because by "ENDSTOP_PULLUP_Z_MIN" I think you mean the endstop Z_min?
I't still on smiling smiley I have my mechanical end stop still connected.

Ah - I assumed that if you were using a probe you were also homing with the probe. Change Z_MIN to whatever endstop pin you are using for the probe. Do make sure you're using a Schottky diode - for a 5V controller board like a RAMPS you should be able to get away with a normal signal diode, but the lower voltages involved with a 3.3V board require the lower forward voltage of a Schottky.
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unf0rg0tt3n
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 05, 2019 02:34AM
Yes thanks! the Z_min endstop will be replaced with the probe and I need 3.3V on RADDS smiling smiley
Thanks for your help
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dc42
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 05, 2019 02:37AM
A smaller and low-leakage alternative to the 1N5817 Schottky rectifier is a BAT43 or BAT85 small signal Schottky diode. We used to recommend these for connecting NPN-output sensors to Duets, which are also 3.3V boards.

Edited 1 time(s). Last edit at 03/05/2019 02:39AM by dc42.


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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unf0rg0tt3n
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 05, 2019 06:58AM
is that even enough since those small units are like 800mV
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MMcLure
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
March 31, 2019 09:51PM
I measured a 1N5819 at a reverse leakage current of 61uA at 12.5V. Is that really enough of a leakage to be concerned about in this application? I'm wondering because I'm planning to upgrade to a 3.3V board myself.
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unf0rg0tt3n
Re: LJ12A3-2-Z/BX onto RADDS 1.6 Board?
April 01, 2019 02:01AM
Quote
MMcLure
I measured a 1N5819 at a reverse leakage current of 61uA at 12.5V. Is that really enough of a leakage to be concerned about in this application? I'm wondering because I'm planning to upgrade to a 3.3V board myself.
I got it all working now, at around 2v is measured high, your idea will work just fine
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