EStop on a v2.4e controller board

Has anyone come up with a workaround to add an EStop on a v2.4 controller board? I just got a new controller board, v2.4e, to replace my v2.3 board that crapped out. I’ve had an EStop on my SO3 almost since the moment I got it three years ago and it has saved my ass numerous times. I wouldn’t feel comfortable running the machine without it.

As other people have already mentioned in the forums, the EStop feature has been removed from the v2.4 boards. Has anyone discovered a workaround to enable the EStop feature in some other way? If I can’t get the EStop capability on this new board I may have to consider trashing my machine and look to CNCRouterParts for a replacement.

Please advise.

“trash the whole thing” is a little drastic.

I don’t have a picture of a 2.4e board, but post one here and I can do my best to help. I’m sure there’s a way.

Multiple options without looking at anything in more depth yet:

  1. Use the pins of the reset switch that’s on the board
  2. I -think- the “Reset” pin on the spindle connector is connected the same, but I need to check it.
  3. Find the “A0” pin on the CPU. I’ll look this up and let you know what I find.
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Trashing the whole thing is not drastic at all. My SO3 is an OG model. My unit was a pre-order, from before they started shipping. I’ve modified my machine numerous times to make it a more feature-rich rig. I added homing/limit switches before they were offered as an option, I added a Z-probe before it was offered as an option, I made a re-enforced Z carriage before it was offered, I’ve added PWM spindle control, and I had an EStop on my machine from almost the very beginning. My SO3 has been a great machine to learn on but I’ve been wanting to upgrade to a larger size machine for a while, like the XL size, and if they’ve taken away the EStop… why should I stick with the SO3 when there’s CNCRouterParts with an excellent alternative?

Anyway, here’s a couple pix of the v2.4e board. Thanks.

Ok, I’ve got a 2.4d board, which is the same as 2.4e. Lacking a picture, I pulled out my board and chased through it.

Interesting trivia, but unrelated:

  1. A3, which is coolant enable, has a via labeled “A3” over by the cpu (the atmega328 QFP toward the bottom of the board). I don’t know anyone doing gcode controlled coolant, so that’s interesting to be pulled out like that.
  2. The PWM output is nicely labeled on 2.4d/e. There are 4 pins above the spindle connector, labeled PWM, 5V, GND, and D13. D13 is spindle direction on GRBL 1.1

I have no idea where the spindle “reset” pin goes. So that’s out.

The CPU is arranged on the board like this:

Pin1 is in the bottom right (there’s a dot in the plastic package)

“A0” is the abort/reset pin for GRBL. It’s pin 23. This is where the old e-stop went. It relies on software to abort, which isn’t really that great an idea. If the software is wedged and still outputting steps, this won’t help.
“Reset” which is probably about as good, is pin 29, and on the header above the cpu. At least that’s guaranteed to stop motion.

Honestly, a better thing to do would be to wire the emergency stop to the power for the router and machine (this may be why they dropped the pins.) .

Why stick with the SO3 when CNC router parts has an alternative? Their electronics are a $1500 add on to their machines, they’re not included. If you’d rather do that (which is also Mach3/4 w/ smoothstepper) then I won’t convince you otherwise. If you’re otherwise happy with your mechanicals, and it’s really the emergency stop that’s got you upset, there are a lot cheaper ways to get an emergency stop. If it’s actually about something else, not sure why you bothered to ask about it.
A box like this can get you an e-stop power cut for cheap ($20):


I thought feed hold wired to an emergency stop would stop the machine in the event of, well, an emergency.

Okay, it’s halftime, so why not go play around a moment or two, eh? I have the NO side of an e-stop button connected to the FEED_HOLD connector on my Carbide Motion 2.4e controller. I fired up the Shapeoko and Carbide Motion (CM4) and ran a bunch of tests.

  • Homing cycle? Feed hold pauses motion, homing cycle failed message.(Restart homing.)
  • Rapid positioning tab (e.g. NW N NE…)? Feed hold pauses motion.
  • Long rapid position (e.g. G0X0Y0 from across the table)? Feed hold pauses motion.
  • Running a job’s G-code? Feed hold pauses motion.
  • Probe cycle, Z-only? Feed hold pauses motion, cycle resumes and completes.
  • Probe cycle, Z and more? Feed hold pauses motion, cycle resumes but the next X/Y goes in the wrong direction, i.e. away from the probe block. (Reset the machine.)

So, by experimentation, it seems that the using a NO e-stop button connected to the FEED_HOLD connector is a cromulent software-reliant emergency pause, except for probing (more than Z-only), which gets funky on resume. It stops all motion (unless the controller’s kicked off a robot uprising), and allows you to easily resume once you’ve moved that annoyingly obstructive clamp that you were sure had plenty of clearance. :sweat_smile:

(I have an IoT Relay on the NC terminals of the e-stop button, so hitting the button triggers FEED_HOLD on the controller (via the NO terminals) and kills the router power (via the NC terminals), stopping stepper motors and spindle.)

Awesome, good to know!

I have an older board, but I use my “ESTOP” pin as a resume for, well, resuming after a feed hold. I also have the machine move to a “parking” position (Z all the way up) on a Feed Hold. I’ve never had to use my E-stop since.
Here’s my E-stop, by the way.


My opinion, because no-one asked is that if there’s really an emergency, as in Emergency-stop, then all power should be killed to the machine. I looked at this a couple years ago when I first got my machine, thinking I should just pause my machine. Several folks mentioned to me at that time the same thing I mentioned in my opinion above, and it made sense. So my E-stop button now kills my Dewalt and my SO3 by cutting the power. Mechanical things fail, electronics fail, software errors out, cutting the power to all is usually a pretty solid way to stop everything.



I certainly concur that stopping EVERYTHING in an emergency is a good idea, and having an emergency button does that. I would also suggest that, at least to those of us who are new enough to make normal mistakes, being able to pause and continue, is something of exceptional utility.

I took care of that by having a nice red mushroom button for those “oops” moments, plus an easy alternate way to kill all the power!!! I highly recommend the former for people like me who are still getting up to speed, and the latter needs no recommendations, as it’s just smart.


EXCELLENT NEWS!!! Thank you @ClayJar Nathaniel for your hard work!

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