Running latest Mach4 release with PMDX SmartBob on a windows 10 machine. Homebrew CNC router with a Gecko G540. Been working fine for a few years and now I'm attempting to install and configure a simple touch probe. The probe is connected via a 2 pin connector I installed on my control box so I can disconnect it. I configured Mach4 and I see the probe triggering properly when I touch the alligator clip to the probe. So I know that is all working. However, I notice that the probe LED (diagnostics panel) sporadically flickers when the probe is not touching anything. If I disconnect the probe from the controller, it does not flicker.

I discovered this while debugging the machine not probing. When I initiate a simple probe Z, the Mach4 screen does an odd flicker pattern on a bunch of the displayed controls and then reports "ERROR: No contact with probe". I thought maybe the odd sporadic flicker indicated a problem so I disconnected the probe from the controller. The Probe LED now does not flicker at all. But if I attempt to probe Z (and I had my hand ready to hit ESTOP since the probe is not connected and can't possibly trigger) the same screen flicker and error message occurs. So now I don't think the issue is the probe. I can't find anything on the PMDX forum or FAQs but did find this thread here (with no resolution given) https://www.machsupport.com/forum/index.php?topic=39830.0

The input is set to PROBE (pin 13) and not PROBE1.

Anyone have any suggestions for debugging or solving this?

Cheers,
Michael

G31 has the same behavior.

I pulled out an old machine with Mach3 installed and using the same SmartBob and probe, everything works properly. After 10 years with Mach3 I have to say I am underwhelmed with Mach4 and all of its issues. Definitely a "if it ain't broke don't fix it" situation for me. I think it is time to move back to 3 or find another option.

I don't use a probe but do use the Probe input for a tool setter.
Never had a problem.
I would check the probe and/or wiring.
I use an ESS and it has noise filtering settings for the inputs.
Have you tried that if it is available on your controller?

Thanks Bill. What is odd to me is that exactly the same hardware and configuration works under Mach3 but not Mach4. This - to me - points to the driver and/or the Mach code itself. Some folks apparently get it working with the same setup I have, so that is even odder. It shouldn't be this brittle. I've been a Mach user for 15 years and this is the first problem I have not been able to solve - and it is a silly simple problem. The PMDXSmartBob doesn't have noise filtering but I have installed a capacitor to filter noise. It wasn't needed under Mach3 but I added it when I first experienced this problem.

The other thing that perplexes me - my probe can be unplugged from the control box. If I unplug the probe I get the same behavior. Unplugged, there are 6" of wires inside the box and it is noise filtered. What *should* happen, is probing should work but would - of course - crash if I didn't estop since there is no way to trigger. But this doesn't happen with the probing macros or G31 - I just get the screen flickering and hang. I've captured debug logs and there is nothing special in them that indicates a problem. Just very perplexing.

Here's a simple question - if I remove all wiring to the probe, I mean disconnect it from the G540 and the ground, but keep the Mach4 and PMDX-411 configuration for probing - shouldn't a G31 initiate a probe cycle? For sure, the machine would crash because there would not be a signal that the probe was activated but shouldn't Mach4, the 411 and G540 all "think" a probe is there (this is a NO probe)? Well, I did this experiment and get the same bad results described above. So this really does point to an issue with Mach4, the PMDX driver or the 411 itself.

Are there any other tests I can do or is this a lost cause and I need to abandon hopes of using a probe or go elsewhere?

It sure looks to me like you are getting noise in the system.
A bad connection?
I have never used a G540 so do not know anything about it.
I use an ESS and PMDX-126.
I have had strange things happen with a bad ribbon cable between the 2.

I don't know how a bad connection or noise can be the culprit with the "completely detach the probe" experiment I just described. Unless a bad connection on one of the other ports would/could crossover to the vacant probe port? And 1) probing works fine in Mach3 and 2) prior to adding the probe, everything else worked fine in Mach4. That's why I'm perplexed. The PMDX-411 connects directly to the G540 so there is no ribbon. It in turn connects to the PC USB port.

USB stinks for machine control.
Just because it worked fine in M3 does not mean anything.
M4 is much better at everything and will see things M3 did not.
You have something causing the spurious signal.
Bad connections?
Bad usb cable?
Noise in the control box having nothing to do with the cable to the probe?
something

The spurious signal is gone now actually - after rewiring it and adding a capacitor filter. At least I do not see the led probe flicker now but the behavior in Mach is the same. G31 and the probe macros all basically hang with no meaningful info in the logs.

I've whittled down to the very simplest setup I can imagine now. I realized I could disconnect all home switches and probe wiring and simply have the steppers wired. Then keep the probe software configuration without an actual probe attached (since it is NO). But this fails in the same way also. So this simple setup consist of the G540, wired to a 48V power supply 6" away all in an aluminum case. Then, on the outside of the case, on the front panel of the G540 are the three DB9 connectors to the steppers and the DB25 connected directly to the PMDX-411, which is connected to the USB port on my computer.

I'd consider moving to something else but there really aren't that many options without throwing a lot of money at it. My lathe has an Acorn controller with ethernet primarily because I built that machine after PCs with parallel ports became hard to find and modern OS's won't run on them.

I don't like throwing new parts at a problem but I have no idea on additional tests, diagnostics are re-wiring I can do to resolve this issue.

I am now down to a minimally configured G540. Shielded wires (with proper shield grounding to the steppers) and no other connections other than power in the control box - which is an aluminum box and the enable pin to an e-stop (and I did test jumpering this to eliminate noise from the switch and wiring). The power supply is a quality 48V Mean Well (I use these on all my CNC machines).  That's it, no other wiring in the box. The PMDX-411 is connected to the G540 outside the box and the USB cable runs to the laptop. I suppose I could go full-monty and wrap the USB cable with copper foil and ground it - DIY shielding - but I am not convinced that will help.

So, with this configuration, I can jog. I can't home of course since no home switches are connected. I do not have the probe physically connected but I do have it configured in M4 and the 411. So, in theory, a G31 command should at least make the Z move. But it does not, M4 screen shows the odd dimming and then just sort of hangs. It is still responsive but I have to click the reset button to get control back. And then about 1/2 the time, this causes the 411 to disconnect.

I agree with Bill about USB, suboptimal for sure. But I'd really like to leverage the G540 and the control box I've already built (and had working for several years). The ESS is compelling but I don't need support for multiple parallel ports. I searched and didn't find a simpler, 1 parallel port equivalent. Maybe someone here has come across one? That would be ideal to convert an existing simple G540 based system to ethernet interface.