Emergency Stop button on Duet 3 for a CNC

  • I am trying to find some info on how to wire and configure an emergency endstop button on my CNC. I found this file but it applies to the duet wifi.https://learn.ooznest.co.uk/Guide/How+To+Connect+Emergency+Stop+Button/25 What pins should I use to connect the emergency stop button or is it best to just run it between the power supply and the duet board killing all the power.

  • Kill the power.

    This will start a flaming debate... but... anything that hits a pin is still dependent to some degree or another on the firmware.

    Kill the power. Or nuke it from orbit. It is the only way to be sure.

  • @Danal so your just saying wire it between the power supply and duet?

  • Yes. If you have multiple, wire them in a Normally Closed loop.

  • Moderator

  • I am an electrical, instrumentation and controls engineer. I design controls and automation systems in industrial and oil and gas industries for a living.

    Your emergency stop ALWAYS cuts power.

    You can have safety stops that use some sensor and stop the process in the programming, but the physical E-Stop buttons are always wired in series with the power to just shut it all down.

  • @Iandayen so if I wire it between my power supply and the duet board that will be sufficient or are you saying it needs to even kill the power supply?

  • @chichirod On the basis that if a PSU burst into flames (albeit however unlikely that may be), that would constitute an emergency, therefore an emergency stop should cut the power to the PSU.

  • @deckingman Ah crap, that makes sense. Ok

  • Depending on the capacitance in the PSU it could leave the machine running longer as well, trade off unless you use a dual pole switch maybe.

  • Both. A true e-stop needs to cut low voltage instantly, so that all machine motion stops, and/or attempts to move (i.e. crush pressure) stop. In addition, it should open a contactor, relay, or SSR, or whatever, on the 'mains' feed into the Power Supply.

    Having said that, my CNC estops (plural, it is a big machine) are 'normally closed loop' wired to the low voltage supply to the controller board. They stop the machine instantly when hit (standard red mushroom mechanically latched).

    If I have a power supply issue, I will hit a mushroom and then pull or kick the wall plug. I'm not saying this is best practice... I'm just saying that's the compromise/balance point where I am comfortable.

  • My EPO setup has the locking mushroom connected to the reset header on the Duet3. When it latches, the Duet3's processor immediately stops so it's not software dependent and since I also control my 24v PSU from the Duet3's ATX pin, the mains input to the PSU is also cut. As long as the reset pins are shorted, the processor will stay halted. On the same control box, I also have a toggle switch that can immediately cut the 5V to the Duet3 in the event I really need to power cycle it.

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