Help with Z Probe Normally Closed and e stop pins

I got a z probe to do a semi-automatic tool change, its normally closed.

The problem is that I cannot mix this probe with a touch plate because it’s normally open, its there a way to use the estop pins to use the the z probe?

If not, I can make a normally closed touch plate, but don´t know if I can set grbl to use it in that way.

You can convert a NC circuit to a NO (and vice versa) with a jellybean BJT and a resistor or two. I also have a NC work probe that required an interface circuit to function properly with the C3D board. I don’t believe it’s possible to use an e-stop input for probing unless you’re willing and able to hack on grbl itself to accomplish it.

I would recommend converting your z probe to make it NO and then just placing it in parallel with the touch plate. The C3D board’s probe input is pulled up to 5V and is active-low. If you’re comfortable reading a simple schematic and wiring it up, I can document what worked for me.


Hi Sean!

Yes it will be nice to have those shematics, :metal:

Here you go. This is what worked for me.

Sorry that the schematic is re-drawn from memory; the exact identity of the NPN transistor and value of the resistor aren’t top-of-mind, but they’re not critical in either case. I want to say I used something like a 2N2222. Just make sure not to exceed your transistor’s base current specification - with a 10k resistor this ends up being in the ballpark of 0.5mA which is fine for a 2N2222.



I will try this as soon as I can find an electronic store open jajaj. :v:

Take a virtual beer! :beer::beers:

It worked great!


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