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Messages - Walter

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  I just got done building my controller boxes (using the 126 and ESS as well), but haven't tried to test it with MACH 4 yet.  So I won't be able to help with that portion of your build, but I can answer a couple of your questions.

  You should use a shielded cable to connect your computer and ESS.  The shielding will ground the ESS to the computer's ground.  The 126 has two grounds.  The PCgnd is connected to the computer's ground (and the ESS and outputs) and should be separated from the other ground labeled GND which you'll see on your inputs.

  If you have a multimeter, set it to the ohms setting and test the PCgnd to the GND, if your multimeter does not read 0L or something else to indicate infinite resistance, then you have a short between them and this can cause noise which could interfere with the CNC's control signals.  I believe I read somewhere on this forum that the GND should also be grounded to you case, but I would suggest you do some research before doing so.

  Have you tried testing it without the E/S connected?  The E/S must be a NC (normally closed) switch, since the 126 will not work without the E/S port being grounded.  The 126 should have arrived with a jumper between the E/S port and GND.  A good practice is to test with the least number of variables. 

  Does your homing switches have any indicator lights?  You can use them to test each switch seperately to verify they are connected and functional.  The 126 will also have an led indicator next to the input port the switch is connected to and will light up when the homing sensor is activated. 

  I would test your hardware before trying to connect it to the computer and using the MACH 4 software.  From what I understand, the MACH 4 software can be a trial, especially when you are getting started.  There is a whole section of the forum dedicated to just MACH 4. 

  For some odd reason, the forum hasn't had a whole lot of activity and the owners are not as responsive as we would like, but I have seen them answer questions here and there.  I would imagine they see a lot of the same questions and probably expect us to do more searching on our own. 

  I hope this helps and best of luck to you.     


The "Probe Trigger" light on the PMDX-179 was designed for a digitizing
probe, which has the reverse action of a touch off probe. Your could get
it to behave as you wish by enabling the "Merged mode" for probes and
move your touch plate to the other input. You will need to put a jumper
in place on the old input point so that it is not always providing a signal,
and also reverse the polarity in Mach4 or the SmoothStepper setup. I am
not sure how it is done under Mach4 with the SmoothStepper plugin.
If the LED on the Machine Diagnostics page lights up when you touch the
ground to the probe input, that should be correct. The LED on the PMDX-126
should be off until you touch the probe input to ground.

I know the original poster (qahrens) had used the quoted solution successfully; however, I wanted to present an alternative solution for those that are just now encountering this issue.  This solution does not require the PMDX-126 to be configured into "Probe Merged Inputs" mode, nor require an extra input pin from the PMDX-126, but it does require an additional 12V relay, which are fairly inexpensive. 

I purchased the PMDX-179_EXT and made a remote status panel very similar to the PMDX-179_PAN. 

Attached is the wiring diagram for my solution.  If you would like to implement something like this, you'll need the following items (most if not all are available on Amazon):

  1.  A small metal box (search for: Aluminum Econobox) large enough to mount 8 - 12v LEDs and a switch (items 2 and 3)
  2.  8 - 12V LEDs (my color selection is in the attachment)(search for: Indicator Light 6mm 1/4" Waterproof IP65 Metal Signal Lamp 12V-24V AC/DC LED)
  3.  A small momentary SPST button (search for:  Momentary Stainless Steel Metal Push Button Switch)
  4.  A 12 wire cable (search for: 22 AWG 12 Conductor Stranded Cable)
  5.  A 12 pin aviation connector to connect remote status panel to the CNC Control box (search for: Metal Aviation Connector M20 - 12 pin) (alternative: Nylon Cable Gland)
  6.  Nylon Cable Gland to connect cable to remote panel box (item 1) (search for: Nylon Cable Gland)(alternative: could also use an aviation connector)
  7.  12V relay (search for: 12V Relay Module with Optocoupler High or Low Level Trigger)


  1.  The 8 LEDs cannot draw more than 100 mV; the ones I got on Amazon drew ~2.5 mV each. Otherwise, an external 12V power supply will be need.
  2.  If a LED on the remote status panel is being used for the Motor Power:
      a.  PMDX-179, JP1 will need to be set to External, after first testing with the on board LED
      b.  The GND for the Motor Power and Test/Reset Switch is NOT the same ground used by the LEDs on J3 (PCgnd) and must stay isolated
      c.  Motor Power Supply needs to be 80V or less
  3.  12V Relay needs to be configured to trigger "Low"
  4.  Due to parallax error of the PMDX-179 image in the wire diagram, lines were added to point the silkscreen print on the PCB to the correct terminal location
  5.  The PMDX-179 on board "Probe" LED will stay lit when the probe is not activated (i.e., pin 9 of PMDX-126 J12 (labeled "15") is connected to ground); however, if the relay is connected correctly, the "Probe" LED on the remote status panel should not be lit until pin 9 of PMDX-126 J12 (labeled "15") is connected to ground.

I went through the quick start procedure with nothing connected but the AC. Checking all the jumpers I found that J4 was in the "ON" position; I set it to "OFF". On power up the EStop comes on then off as it should (I left the factory jumper across the EStop pins). The power light stays on as it should.The status light blinks with the EStop light. The outputs enabled light does not turn on.

Your suggested tests:
1. I don't have a 5V LED but a voltmeter measures 0.48 DCV  between pins 2 & 6 on J7.
2. With the suggested configuration, the K2 relay does not activate when the test button is pushed.

What is the next step? Can I return the board for repair/replacement?


For the second test, pushing the test button wasn't to activate the K2 relay.  The purpose is for the PMDX-126 to accept the configuration change to have the K2 relay activate when the outputs are enabled.  Once the K2 relay is configured, there should be continuity (near 0 Ohms) between NC and COM if the Outputs are disabled, and continuity between NO and COM if they are enabled.   

My thought was that the "Outputs Enabled" LED could have failed, when the outputs were in fact enabled.  The onboard LED and J7 pins could be linked and thusly both are failing for the same reason.  Activation of the relay may not be linked to the LED, possibly giving an independent way to verify the outputs.

If it was me, even if the outputs were enabled as expected, I would want to have the LED working and would return the board for a replacement, assuming it is still under warranty.

Did you figure this out, in the same boat now with my DIY machine and haven

I am also building a DIY CNC machine and haven't quite gotten to the point of mapping the ESS ports, so perhaps we can figure this out together.  From my understanding the PMDX-126 can be configured to use one or two parallel ports.  I believe the ESS has three parallel ports; however, I would assume configuring the PMDX-126 to use two is the norm and the PMDX-126 is configured for a "normal" mode. 

The ESS mapping should be fairly straight forward, and the manual for the PMDX-126 states (in section 11) which pins are mapped to which parallel port pin.  Generally, the terminals on the  PMDX-126 that have a connection to a parallel port pin are named for the parallel port pin it is associated with where numbered names are for parallel port 1 and lettered names are for parallel port 2.  The numbers in quotes (e.g., "13" or "15") directly correspond to the same pin on parallel port 1.  The lettered inputs are not so obvious, but from the manual, "E" -> pp #2, pin 11; "F" -> pp #2, pin 12 and so on.  Again this is assuming the PMDX-129 is configured for a "normal" mode and not an "expanded" mode.

The PMDX-126 has several other pins that are not connected to a parallel port.  For example, the PMDX-126 has a few unregulated 12v and regulated 5v output pins (with limited current output capability), and two ground types (PCgnd and GND) which should never have continuity with each other (i.e., should never be connected together).  The PCgnd is connected to the parallel port's ground pin and the GND pins are connected to each other and at least one should be connected to the machine frame and main power safety ground (section 10).   

I'm sure you already knew some or all of the above.  What is your setup and what particular challenges are currently facing?

  I believe the JP3 jumper is shipped in the off position.  Just to be clear, you are powering the ESS from an external 5V power source and not through the PMDX-126.   If this is the case, then this jumper should be fine in the default setting.  Are you getting power to your ESS?  Otherwise, what led you to question the JP3 jumper? 

  When you started to install the new PMDX-126, did you follow the Quick Start Guide in the PMDX-126 manual to test and verify your PMDX-126 was functioning correctly before proceeding with the install?  It is best to verify it is functioning correctly and then slowly add new connections, retesting after making the new connections.  Having everything connected before testing makes it very difficult to isolate issues.

  Your description of your issue is quite vague, and additional details would make it easier to guide your troubleshooting efforts.  Are you sure the issue is with the PMDX-126 and not with any other component?

  If the "E-Stop" light is on (bright red light), then the "Output Enabled" light will not come on.  Do you have an E-Stop button installed with a normally closed switch connecting the E-Stop pin (pin 4 on J13) and the GND (pin 5 on J13) together or is there a jumper installed between these two pins?  The PMDX-126 is shipped with a jumper installed between these to terminals and the PMDX-126 is designed to only function when these two pins are connected together.  Are there any other faults, perhaps from external components such as motor drivers, that are causing pin 6 (Faults, active low) to activate.  The PMDX-126 will also disable outputs if faults are present (or it thinks there are faults present).

  A couple quick tests you can perform to determine if the "Outputs Enabled" is in fact on (e.g., the "Outputs Enabled" led is not functional, but the rest of the board is):
    1.  Connect an 5V LED between J7 pin 2 ("OE") and pin 6 ("PCgnd).  The LED should light if the outputs are enabled.
    2.  Configure the K2 relay to be enabled when outputs are enabled.  JP2 connected between pin 2-3 "multimode" and set dip switch "Config 8" to open (off), then press the "Test" button or perform a power cycle.  Connect a LED or something else (contactor, etc...) to the K2 terminals and if the outputs are enabled, the device connected should activate if it is connected to the NO terminal or will deactivate if connected to the NC terminal when the outputs are enabled.

  Without more information, I can't think of anything else to verify the PMDX-126.  If you are still having issues after following the suggestions presented, then follow-up with additional information.  Best of luck!

From my research, your symptoms seem consistent with EMI noise.  Without knowing your whole setup, it is difficult to know for sure. Is there a condition or sequence of events that it always occur?  Does it occur when the spindle motor/VFD is off or on?

The biggest culprit for noise is the VFD.  It is advised to put an EMI filter between your main power supply and the inputs of your VFD to prevent noise from bleeding back to the power supply.  If your computer is on the same circuit as your VFD, then the noise can definitely reek havoc. 

The next thing is to be sure your shielding is grounded.  All signal carrying wires should be shielded with proper grounding.  The description of the PMDX-424 says the USB port is isolated electrically.  This by itself should help with EMI interference, so I suspect there is a strong EMI source somewhere. 

Lastly, be sure no signal wires run parallel to any power carrying wires.  If they need to cross, cross them with a 90 degree joint and if they need to run parallel, be sure they are separated the recommended distance or run them in separate conduit.  My experience with EMI is limited, and there are plenty of resources on the internet on the effects of EMI and how to minimize it. 

Hopefully, this is the issue and you can easily correct it.   

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