Trouble Getting NPN probe to work



  • Hey Guys,

    I've been scratching my head over this one for a little while now and thought it was time to ask for some advice. The image below shows how I have everything hooked up. For some reason I'm getting 24v between ground and signal, on the probe which I thought wasn't supposed to happen with a Schottkey diode. I'm using a BAT85 because DC42 suggested that or BAT43 and since I don't know the difference, I just went with the 85. I'm pretty sure I have it wired right based on the wiki, but I don't know for sure. It may be the case that the 43 was the right call, so hopefully someone can set me straight if that's the case.

    When the signal wire and V- from the terminal are connected, the LED on the sensor is on and gets brighter when triggered and the voltage drops down into the mv range. When the wire is not connected, the LED is off unless it is triggered, then it turns on.

    As a side note, I have the V- going from the terminal to the ground of the E0 header because i didn't want to run another wire for it since I have a pretty substantial wire run up to the extruder area, but I can do that if there is a problem with this, I just figured since it's the same ground, it shouldn't matter, but again, I'm applying noob logic here. I have a single V+ and V- leading up there and it splits off to power my hotend fans, otherwise I'd use the same V- wire to go straight to E0.

    Diode https://www.amazon.com/dp/B00DK85E14/ref=cm_sw_r_cp_apap_kFYq1ZYYIPyGk
    NPN Sensor https://www.amazon.com/gp/product/B0052WM522/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

    (Update: image updated since I had it drawn wrong)

    My config is setup as follows:

    M574 X1 Y1 S1 ;
    M574 E1 Z0 S1
    M558 P4 I1 X0 Y0 Z1 H5 F120 T6000

    Everything else works fine including X and Y homing so it's really just the probe that I need to get working before I can push on. I tried my best to search around for a solution but I'm not an electronics guy so I'm working with a fairly limited understanding of how some of this stuff works so please be gentle 🙂 If I've left anything else out that might be helpful to diagnose the problem, let me know. Any help would be greatly appreciated!



  • I think you have the SIG wire going to the GND and the GND wire going to the E0 Stop.

    https://duet3d.com/wiki/Duet_WiFi_wiring_diagrams



  • @jmjcoke:

    I think you have the SIG wire going to the GND and the GND wire going to the E0 Stop.

    https://duet3d.com/wiki/Duet_WiFi_wiring_diagrams

    Gah! I just had a look and actual wiring is correct but my drawing is incorrect, sorry about that. Green wire is coming from diode/sig and the black one is going to ground on the terminal.



  • Or if anyone knows how to disable homing before a print altogether, that would help me out in the mean time until I can get the Z probe working lol I can't print anything without one of the two and I can't even seem to figure out how to just disable it so I can position manually and print something.


  • administrators

    You have the BAT85 diode the wrong way round. The end with the stripe should be connected to the sensor, the other end to the input pin on the Duet.



  • @dc42:

    You have the BAT85 diode the wrong way round. The end with the stripe should be connected to the sensor, the other end to the input pin on the Duet.

    Yeah, that seems to have done it. I'm starting to question whether or not I can read goodly 😕

    Thanks for for the help David! I can print now! 🙂


  • administrators

    Thanks to your wiring diagram, it was easy to diagnose!

    We should add more diagrams to the wiki. What do you folks use to draw wiring diagrams?



  • I just used Photoshop but I'm sure there is "proper" software out there.

    Yeah I think official pictures on the wiki for for the tecnically challenged such as myself might help, especially since anyone can toss a misleading diagram that looks proper enough on the interwebs and someone who doesn't know better could follow it and possibly do some damage.

    Speaking of which, I should amend my drawing so some poor soul doent make the same mistake because as me lol


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