NPN Probe on Z axis

  • Hi all,

    Firstly I have read and reread the wiki but cannot seem to find the solution to the issue I am having with using an NPN NO Probe for the the z axis endstop.

    I have it wired up with a diode and connected to the E0 STP pin. When triggering it manually (by placing a metal object under it), both the LED on top of the probe and the LED on the DuetWiFi lights up. Which to me indicated the hardware is working fine.

    However when I home the Z axis, when the probe is triggered it does not stop the motor so the z axis just keeps moving up.

    I must be missing something in the config. So if anyone can help, that would be great.



    ; Endstops
    M574 X1 Y1 S0 ; Define active low and unused microswitches
    M574 Z0 E1 S1 ; Define active high microswitches
    M558 P4 I1 X0 Y0 Z1 H10 F120 T6000 ; Set Z probe type to switch, the axes for which it is used and the probe + travel speeds
    G31 P500 X28 Y12 Z1.20 ; Set Z probe trigger value, offset and trigger height

    G91 ; relative mode
    G1 Z4 F200 ; raise head 4mm to ensure it is above the Z probe trigger height
    G90 ; back to absolute mode
    G1 X100 Y100 F2000 ; put head over the centre of the bed, or wherever you want to probe
    G30 ; lower head, stop when probe triggered and set Z to trigger height

  • administrators

    Your config looks ok to me. I suggest you use M119 or the web interface to check whether the firmware sees the sensor as triggered when the LEDs turn on.

    Some people seem to need to use a Schottky diode when connecting the probe output to the endstop input. For others, an ordinary silicon diode works. Perhaps it depends on the sensor.

  • Thanks,

    Using M119 I get

    Endstops - X: not stopped, Y: not stopped, Z: not stopped, Z probe: not stopped

    X and Y work fine, neither z or z prode are activated when manually triigering the probe despite both lights being on.

    I guess I need to source some Schottky diodes.

    The 2 diodes I tried were:

    1N4148 150mA Switching Diode
    1N4007S 1A Silicon Rectifier

  • administrators

    Try a Schottky diode e.g. BAT43 or BAT85.

  • Just an update. The BAT43 diode works perfectly.

    So I now have a fully working NPN Probe with the Duet WiFI.

    I will give the Mini differential IR height sensor a go when it arrives 🙂

    Thanks dc42

  • richardmckenna, how is the BAT43 diode wired into the leads? On the signal lead between the sensor and the controller? Which direction? I am not particularly wise in this area. 🙂

  • i have this sensor and i used a bat85 for it, the untriggered output is at 0.5-0.6V and triggered is showing 0.14-0.2V, im using 24V, i have not attached it yet to the duet. are those values reasonable for duet to be read?

  • administrators

    The 0.5 to 0.6V is unusually low.

  • usually what should be the signal input voltage accepted by the board?

  • interestingly, it seems the signal is being distinguished.

    >>> M119
    Endstops - X: not stopped, Y: not stopped, Z: at min stop, Z probe: at min stop
    >>> M119
    Endstops - X: not stopped, Y: not stopped, Z: not stopped, Z probe: not stopped

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