Proximity Sensors on v2.3 CM board (SO3)

I’ve got a 2015 Shapeoko 3 with mechanical limit switches (running grbl 1.1). The v2.3 Carbide Motion board doesn’t officially support the Proximity Switch upgrade kit. I believe the proximity sensors will provide better repeatability when homing, and I’d like to use them because I have them.

So, can anyone tell me: what’s the operating voltage range of the proximity sensors? And are they NPN or PNP type?

The CM v2.3 board limit switch pins have a common ground, and the inputs are pulled to 3.3V. When closed, the input is pulled to ground. There’s a 12v source with the common ground at the fan header I can use to power the proximity sensors.

I expect a couple resistors and a transistor for each proximity sensor will be required to not fry my CM board, but I’m looking for the simplest effective solution (Other than buying a new board).

I’ve had my S3XXL since 2019, and it still has the original mechanical homing switches. I’ve never run across a situation that indicated a repeatability problem.

Perhaps that is because I’ve always followed a homing cycle with a XYZ rezeroing cycle.

Even with that, I’ve not noticed a practical zero error in the fixed workspaces that I have set up on my table.


I’m with @CrookedWoodTex on this one. I’ll replace my mechanical switches if I ever need to. Do you have specs on the proximity sensor you have?
To more directly answer your question…they are NPN type. Not sure on voltage range, but I think they’re using a 5V source.

The proximity sensors I have are the Carbide3D ones from the shop: Shapeoko Proximity Switch Kit - Carbide 3D

My experience with my lever action microswitches is that they’re good enough most of the time, but not quite there for milling aluminum. No doubt a different mechanical switch could work better…

Oh…those don’t need anything except the correct connection. Just need 5V, Switch Pin & Ground. You’ll need to figure out the common 5V.

Unfortunately the Shapeoko 3 is getting long in the tooth. C3D still supports it but now that the Shapeoko 5 is out there has to be a sunset for the SO3. My advise would be to buy a new controller kit from C3D and solve the proximity switch upgrade problem. Last time I saw the price it was $149.00 but that included the board and the new case required for the new boards. Having an old board will eventually lead to it not working with newer and newer versions of Carbide Motion.

So my advise is to upgrade to prevent premature obsolescence. The SO3 is a great machine and should be around for a while but as all things eventually it will be obsolete.

Over time I have upgraded my original 2016 Shapeoko 3 with proximity switches, HDZ, BitRunner, BitSetter and BitZero. My SO3 is a work horse and works better now than when I first got it. However should my SO3 suddenly disappear I would replace it with an SO5. By the time my SO3 gets to the end maybe a SO10.

I don’t think that would be the case anytime soon — even our newest machines are still using Grbl 1.1, which I would be very surprised at our switching away from in the foreseeable future.

I don’t want to sound like Apple going on about “Apple II Forever”, but we do our best to ensure that no Shapeoko gets left behind — for the software end of things, that’s far easier to update/maintain than the physical side of things.

Thanks @neilferreri . I was hesitant to connect the proximity sensor directly to the input pin, since the microcontroller appears to use 3.3V logic high. But I checked the datasheets on the two microcontrollers and both can handle 5.5V so I’m not concerned. Plus the impedance is so high on the prox sensor it drops to 3.8V when connected to the limit switch pin.

@gdon_2003 I’m a Reduce Reuse Recycle kinda guy, so I’ll use this board until it burns out then repair it or replace. (I prefer the label frugal rather than cheap) :wink:

In case it helps anyone in the future, 5V pins on v2.3 board are shown in the attached photo.

Thanks everyone for your input!

For posterity, here to confirm that wiring directly to the old CM board worked. Wire harness shown below.
Proximity Red - 5V - red on harness
Proximity Blue - GND - black on harness
Proximity black - signal - yellow on harness

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