Ender 3 with inductive probe

I've added an inductive probe to my Ender 3 PRO and now need to build Marlin for it. I have the V4.2.2 board with the STM32F103RET chip (512K).
I've built a level converter using an optoisolator that is connected to the socket reserved for the CRtouch. I still have the original Z end stop switch connected,
and I'd like to continue using this for the Z homing when not performing the bed leveling. Is this possible? The Z end stop will 'fire' after the probe does, and this
will provide a safety factor should the probe malfunction. How do I configure marlin to do this?

You can't configure Marlin to have a safety backup endstop. I would have really like to have that feature.

Enable USE_PROBE_FOR_Z_HOMING to use the probe for homing.

Some other questions then

What happens if I enable the bed leveling (tramming) but DONT uncomment "Enable USE_PROBE_FOR _Z_HOMING" and define the BLTouch port for the probe?

The X position of the Probe will be at the "home" position of the bed when the nozzle is at an X position greater than zero. So do I define the left most probe position as X=0 or X=actual nozzle position when probe is over bed zero? In this case there must be an offset defined between the probe and the nozzle ( in my case the probe is 45mm to the left of the nozzle, and is 5mm in front of the nozzle (so with the probe at Y=0 the nozzle is at Y=5 or with the nozzle at Y=0 the probe is at Y= -5). My probe now is "firing" when the nozzle is at z=.35mm (this can be adjusted up and down, and this assumes the nozzle is a paper thickness above the bed when the mechanical Z end stop is triggered (z=0).

If the function of the Z end stop is transferred to the probe (and bed leveling / tramming is done with the probe but auto home is done with the z end stop switch), then how do I determine and dial n the probe / nozzle offset?

Edited 1 time(s). Last edit at 03/08/2023 11:42AM by kscharf.

It's very unusual to be using a Z_MIN endstop when you have a Z probe. I've seen a Z_MAX used with a Z probe.

It's really hard to adjust the position of the Z_MIN endstop such that you're not crashing into the bed when homing or the head never reached the bed.

"If the function of the Z end stop is transferred to the probe (and bed leveling / tramming is done with the probe but auto home is done with the z end stop switch)" - this is contradictory. If USE_PROBE_FOR _Z_HOMING is enabled then the Z end stop is never used. If it is disabled then homing uses the Z endstop and bed leveling / tramming is done with the probe.

The easiest way to set the Z offset is to enable BABYSTEP_ZPROBE_OFFSET. Enabling BABYSTEP_ZPROBE_OFFSET results in the Z offset being modifed by the babystepping You then use babysetpping to dial in the first layer and then do a M500 to save the new Z offset value.

The ender3 pro 32 bit board doesn't have any MAX end stops. It DOES have a separate input for the BLTouch device, which consists of a probe input and a servo output plus ground and +5v power. I've wired this input up to my inductive probe, using only the probe digital input and ground. At the inductive sensor I'm using an optoisolator as a level conversion, it is a NO switch, so logic level inversion is required in SW.
The BL touch interface is separate from the Ender3 Z axis Z_MIN switch input. I'm leaving that the way it is.

If homing is done via the probe, then software must know that the z home is actually a bit below the point where the probe activates, otherwise the nozzle won't get low enough. So there will be a way to home the printer, tram the bed, then notice that the Z axis homes too high, zero in the right position and save it?

It sounds a bit convoluted, I'd have thought that there would be separate Gcode commands for home z axis, and tram bed. The latter would use the probe, the former could use the probe, or the zmin input (if different). At least if I know that the probe will activate before the nozzle crashes into the bed, the printer will be safe. Then I just need to set the offset between probe and nozzle position for the 'true' Z axis home position.

Yes, it is a pain to wrap your head around all the intricacies of setting up & calibrating your printer.

The Z offset doesn't come into play when tramming the bed. All that matters is the bed is reasonably close to parallel to the head's X/Y plane after tramming. It doesn't have to be that close because the ABL matrix will compensate for any tilt, valeys and peaks in the bed.

After tramming set the Z offset. See my prevoius post on how I like to do it.

After setting the Z offset, run the command to have the ABL flavor you selected do an auto probe to create the leveling matrix. Chances are the probe can't reach the entire bed so you'll have to manualy calibrate some point.