Z-Stop Always Reads Hit / Z sensor always reads 1000



  • Hello,

    I am currently working on rehabilitating a Printrbot Simple Metal using a Duet Wifi board. I have x and y homing working perfectly with the mechanical switches, but getting the inductive PNP sensor for the Z-axis working has been a huge pain. The z-stop sensor always says that it's hit… no matter what I do or how I wire up the PNP sensor. I am using a 10K and 15K resistor in a voltage divider to bring down 12v to 3.3v from the sensor wire of the PNP inductive sensor that's connected to the z-stop pins.

    One thing that leads me to believe that it's a configuration issue is that even when I disconnect all the wiring from the z-stop port... the machine still reads that the z-endstop is "hit" (YES) 100% of the time. The X and Y z-stops correctly read "NO" for their status until I manually move the print bed to the edge, at which point they update to "YES".

    I'd like to know if there's anything in my configuration that could be causing the z-config to not work properly.

    https://github.com/dirtybirdnj/printrbot-duet-wifi/blob/master/config.g

    Thanks!



  • Any idea what voltage the PNP sensor is running at ? If it's 5v or worse 24v are you using a couple of resistors to act like a voltage divider to drop down to 3.3v levels ? Before switching to the BLTouch I was using a PNP inductive sensor with great success.

    Jeff



  • Jeff,

    The sensor itself takes 6-30V in… so I'm pulling 12V off a cable from the ATX power supply I'm using.

    The output wire of the sensor is being stepped down from 12V to 3.3V.

    I think the next thing I'll do tonight when I get home is verify that information / voltages... but regardless of that wiring it doesn't make sense to me that the z-stop sensor ALWAYS says it's triggered even when nothing is plugged into the port.



  • Here is how I'm setup now for the BLTouch

    M558 P5 I0 X0 Y0 Z1 H3 F300 T9000

    You may want to look at the I and H parameters.

    I also have

    M574 X2 Y2 Z0 S0

    The Z0 may be on interest to you.

    Jeff


  • administrators

    @dirtybirdnj:

    Hello,

    I am currently working on rehabilitating a Printrbot Simple Metal using a Duet Wifi board. I have x and y homing working perfectly with the mechanical switches, but getting the inductive PNP sensor for the Z-axis working has been a huge pain. The z-stop sensor always says that it's hit… no matter what I do or how I wire up the PNP sensor. I am using a 10K and 15K resistor in a voltage divider to bring down 12v to 3.3v from the sensor wire of the PNP inductive sensor that's connected to the z-stop pins.

    That won't work because it doesn't provide a strong enough pulldown. Use the Z probe connector instead and adjust the resistor values. See https://duet3d.com/wiki/Connecting_a_Z_probe#PNP_output_normally-open_inductive_or_capacitive_sensor.



  • I missed that he was using the z-stop axis and not the z-probe.



  • First off, THANK YOU! Really great to have a problem / question posted in the morning and have a really good solution / answer later in the day! Amazing support, I already love the Duet board but you just gave me another really good reason to recommend it to others. Community around software/hardware is so important.

    @dc42:

    That won't work because it doesn't provide a strong enough pulldown. Use the Z probe connector instead and adjust the resistor values.

    I had read the page you linked seemingly 100s of times but it never occurred to me that I was using the wrong port! This is a really exciting suggestion because it provides a VERY good reason that my sensor output is wonky in the web UI.

    Just to be super… ultra clear on which port I should be using... I made a little diagram...


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