E-Stop awareness

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    Douglas Craig

    I’m currently converting an X Carve into an Ex Carve using a Pro 4 axis board, UC100, and Mach4. I have it wired up so the e-stop switch is between the power supply dc+ and the Pro board. Naturally, if I hit the e-stop it cuts power to the board and drivers. However Mach4 doesn’t know I hit the e-stop, so it keeps chugging along.

    What is the best practice for making Mach4 aware of an e-stop with the Pro board? I was thinking about adding a NC relay to ground pin 11 when the e-stop is activated. Any reason this wouldn’t work?

    Richard Schmidt

    There used to be a place on the old Yahoo group where you could find several helpful files. I didn’t find that on this new forum. I was looking for the “Estop and SCP.pdf” file.

    I have attached the pdf file from my files for the E-stop and SCP (Safety charge pump). I have this setup on my Hobby CNC controller and it works very well. This would solve your issue. Hope this helps.

    Rich Schmidt



    The old forum is still available for reading: https://groups.yahoo.com/neo/groups/HobbyCNC/info.

    I’m not familiar with the 4AUPC boards, but I’ll give the drawing a look-over.


    Well, that isn’t the proper way to wire the switch. It is behaving exactly as I’d expect it to (e.g. it will do nothing).

    The e-stop switch needs to be connected at one side to the GND of TB5 and to one of the remaining open pins on that same connector (Pin 11, in your case). The pin needs to be pulled to ground, not V+ (it’s already at +5V).

    Another option is to put the e-stop switch in the same chain as the limit switches. See FAQ Home & Limit Switches. Regardless if it is a limit-reached or an e-stop, you want everything to stop moving.

    You could go the relay route, but I think it’s overkill.

    Douglas Craig

    My thoughts on the e-stop are that I’m using it in an emergency; the machine is doing something dangerous. Rather than telling Mach4 to stop, I want the e-stop to cut power to the motor drivers, that way it will stop no matter what is happening. If the e-stop is only wired to signal Mach, a software glitch could disable the e-stop switch.

    If it is wired to a NC relay on the out side of the switch it can accomplish both goals. It will cut all power to the board, and the relay will close and ground T11, letting Mach know there was an e-stop. At least that’s my hope. A more ideal situation would be having pads on the board that would interrupt power to the drivers, but not the rest of the board. Anyone who wanted a switch wired like I do could do it and anyone else could install a jumper.

    I will likely also have a stop button that only signals Mach wired in parallel with the relay.

    Douglas Craig

    On reflection, I think the real question I should have asked is whether I can short T11 directly to ground without damaging the board, or if I need a current limiting resistor.

    Given that the rail is for limit switches I would assume it won’t damage the board, but it’s better to ask and know instead of assume and blow out something on the board.

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