Z probe switch logic.

I am building a new printer and have just made a retractable
z probe unit.

The probe is lifted away from the switch when the bed
touches but is also lifted away when the probe is in the retracted position.

I wanted to do it this way to negate any sloppiness in the
servo arm. The hardware at least is working very well but am wondering if the
firmware will get upset with the z probe indicating bed touch when retracted.

Im hoping it only looks at the switch during the probing

Also any help appreciated (links etc) about moving the servo.





  • You mean in retracted position it triggers high signal I guess. That should be no problem as long as it is not triggered when you start a real z probe, cause then it stops going down when signal is high.
  • Indeed, i hope the switch position is irrelevant until after the z probe is extended (perhaps with a bit of delay) and hope it is ignored again BEFORE the z retract is triggered.

    Either way i hope its like this
    Ignore z switch (during all other times)
    extend z probe
    monitor z switch while moving bed
    get z position (at various locations?)
    ignore z switch
    retract z probe

    If its something like this there should be no issues.

    Are there some gems of info somewhere on servo positioning? Cant seem to find a main wiki on it.
    The servo puts very light pressure on the switch via a printed coil spring. See pic. Hoping it will be very accurate..

    Thanks for help.

  • Serve position is set with M340. See repetier.ino for full command details. Run the command in z probe start/end gcode to set position. If possible autodisable servo after a while so it does not jitter any more from pressure. Will surely increase life time.
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