Z Probe and min Z appear to be mutually exclusive

Hi All,

My old printer (my take on a Prusa i3) used Repetier firmware 0.91 on a Sanguinololu board and I never had issues with zeroing out the Z axis despite never having any Z min or max sensors, I would just jog to the required height, home X and Y, then set all as home and off I would go with the print, I regularly used this Z jog capability and a small piece of paper to manually level the bed.

I have recently built a new printer (Ord Bot Hadron) with a Ramps 1.6 board running Repetier firmware version 1.0.3.

The above procedure does not work on the new printer/firmware, since wherever the printer happens to be when it is powered on is assumed to be X=0, Y=0, Z=0 and unless you can home to a limit switch it will not go below that value.

Having a Z min sensor seems somewhat pointless when you want to fine tune the Z height prior to a print, unless it can triggersbelow the bed height somewhere off the print bed, you are either going to hit 0 above the bed and end up printing in the air, or crash your head into it and then jog up to the real print height.

Having failed to achieve the functionality I had with the old firmware/printer, I am trying to get the auto leveling feature to work, since that at least allows for a Z offset after the Z probe has triggered.

I have read the relevant documentation and numerous forum posts but am still having issues.

As far as I can tell, to do what I want, I need to set the Z min and Z probe values to the same pin - However, the outcome is not as expected when using M119 to probe the limit switches:

If I define either one of them independently and manually trigger the microswitch, it toggles from L to H as expected.

If I define them to both use the same pin, and manually trigger the microswitch, then the Z probe will toggle from L to H, but Z min will stay as L.

If I define Z probe and Z min as different pins but physically wire them together, only then will they both toggle from L to H at the same time.

Additionally, despite setting Z_PROBE_BED_DISTANCE to 10 in the Configuration.h and in the eeprom settings, it still lifts up 30mm for every probe.

I have also yet to persuade the servo to move, but that is an issue for another day, worst case I can manually move the servo arm for bed levelling fo now.

Many thanks in advance for any pointers as to what I am doing wrong.


  • The endstop output for M119 is correct. With z probe and z min homing it will have zmin always low. Many probes trigger before you are at z min so being the same device we can not have is signal z min as well.

    You can move below 0. Just send G1 S1 to ignore positions allows you go lower then 0 with G1.

    Z_PROBE_BED_DISTANCE is not always used. It gets used by G32 and G33 when you have homed before. G30 will normally go back to start position.

    Does servo work when sending M340 manually? Note that you need a extra 5-6V power to power the servo. The boards 5V should not be used for this normally since the regulator has not enough power for normal servos.
  • Many thanks for the explanation regarding the signals, your explanation makes sense, although my experience with the G32 bed leveling procedure appears to require inputs from both Z probe and Z min. If missing one of the Z min or Z probe, parts of the procedure will crash the head into the bed as the procedure is expecting a response from one and then the other. With both wired to diferent pins and to each other, so both trigger at the same time, at least the procedure completes without a head crash.

    I was not aware of the G1 S1 call, that is a huge help, at least I can now manually level the bed by moving the head around and then using M114 to tell me the actual Z heights and adjust the bed acordingly.

    The servo does absolutely nothing, even with manual M340 commands, but I do have it all wired to the ramps board.

    To be fair, the servo part and possibly even the auto bed levelling seems to be more hassle than it is worth, especially if I need a separate power source for the servo. One of the appeals of the Ord Bot is the clean wiring, 5 extra wires from the extruder area, a buck converter, and not necessarily any great time saving, or improvements in printing, I can probably live without it - I managed with manual levelling on my previous printer for 6+ years
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