MPCNC: Emergency Stop / Feed Hold / Resume Pendant

The Protoneer CNC Shield has pin headers for GRBL’s Feed Hold and Resume inputs, so it seemed appropriate to put big buttons on the far end of the cable:

MPCNC - E-stop Hold Resume switch box

MPCNC – E-stop Hold Resume switch box

The Emergency Stop Push Button Switch Station arrived for ten buck delivered from halfway around the planet.

There’s not much to the wiring inside the box:

MPCNC - E-Stop switch box - interior

MPCNC – E-Stop switch box – interior

I drilled a hole to fit the 6 pin Aviation Wire Connectors  I got for this very purpose:

MPCNC - E-stop switch box - drilling

MPCNC – E-stop switch box – drilling

You could CNC machine a precise D-hole, but let’s stay realistic about the application. Applying a deburring tool enlarged the 9/16 inch hole enough to force the 16 mm threads into it, with the drill press holding the connector perpendicular to the box while I hand-turned the chuck to screw it in.

Although I like the Protoneer CNC Shield, I really really dislike using header pins as connectors:

MPCNC - Protoneer Wiring - SSR

MPCNC – Protoneer Wiring – SSR

Those pins are much too delicate.

The DC-DC solid state relay input connects to the Arduino’s +5 V power supply through the red mushroom disconnect switch. The mushroom is normally closed to turn on the SSR and connect the power brick’s +24 V supply to the motors; it opens when slapped. BRBL will continue about its business, but without any power to the steppers the MPCNC will stop dead in its tracks. Turn the mushroom cap clockwise to unlatch and reset.

The disconnect switch should also kill AC power to the router, when I get around to adding one to the mix, probably through a DC-AC SSR.

AFAICT, the cable should come out of the box on the end with the mushroom switch, putting the “normal” pushbuttons closer to me. I did it the other way around, because I want the panic button to be the most easily reached thing on the benchtop. If I have time to think about it, I can reach around the mushroom to the Hold switch.



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  1. #1 by Konstantinos Ziakas on 2018-03-24 - 10:15

    Hello, this is very interesting job you did there. I have one question on the wiring of the E-Stop switch box (the picture you have from the interior). Actually I see that multiple cables are coming in the circuit. Instead, I have a simple supply cable (2 wires) which supposed to be connected with a motor. Could you please let me know how the wiring should be in order to have it right? The box is pretty much the same with yours. Thanks in advance!

    • #2 by Ed on 2018-03-24 - 10:27

      I finally scribbled a schematic for the thing when I moved the controller under the bench.

      Although the buttons can certainly handle high currents, I used a very supple cable with thin wires and controlled the motor power supply output through a DC-DC solid state relay: pushing the red button shuts off the relay and disconnects the motor power.

      • #3 by Konstantinos Ziakas on 2018-03-24 - 12:41

        Thank you very much for your prompt reply. In fact my wiring options are much simpler. I have a single phase cable to be wired through the box and then go to the motor. The thing is that I have no clue which wire goes where. Maybe these images shed some light (the picture showing the back is on the same direction so emergency stop is on top).

        • #4 by Ed on 2018-03-24 - 16:37

          You have too many buttons! The green and yellow ones are normally open, as they’re intended for machine control functions like Pause and Continue. If you don’t need them, get a single-red-button box to avoid confusion.

          This diagram should aim you in the right direction:
          Line voltage E-stop doodle

          Don’t use a yellow/green colored wire for anything other than the safety ground connection, because it will come back to bite you!

          • #5 by Konstantinos Ziakas on 2018-03-25 - 08:49

            Thanks for the diagram. Actually, the green yellow wire was just to interconnect the buttons (not coming from anywhere). The power supply cable is only 2 cables (the brown and blue). For the sake of the experiment I have used a battery where the brown cable is linked with the (+) of the battery and after the box it should go out to the device (a flashlight just to test). And after the flashlight the blue cable goes to the (-) of the battery. For the time being it seems to work apart from the fact that the green button doesn’t keep the flashlight on when I release it (I think that the power of the battery is not high enough as it needs 240V). In any case I re uploaded the image with descriptive test for each cable. And I would appreciate if you could tell me if what I did makes sense. Remember, I have a 2-cable power supply (no ground).

            Thanks a lot for your help!

            • #6 by Ed on 2018-03-25 - 10:16

              You should not proceed with what you’re trying to do, because you do not understand the difference between normally open and normally closed switch contacts.

              I don’t know whether the diagram I sketched will do what you want, but I cannot explain it more clearly than I already have. We do not share the vocabulary and concepts required to describe the components and their actions.

              You must find a local tutor to help you gain an understanding of basic electrical and electronic concepts before proceeding: one simple mistake with power line voltages will kill you stone cold dead.

              I don’t want to discourage you, but I do want to keep you safe!

            • #7 by Konstantinos Ziakas on 2018-03-25 - 11:38

              I think you’re right! Too risky for just a simple thing. But anyway thanks for your time and precious comments! Best regards!

            • #8 by Ed on 2018-03-25 - 13:28

              None of us started out knowing this stuff, so start simple and keep on tinkering …

  1. MPCNC: Button Box Wiring | The Smell of Molten Projects in the Morning

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