Endstops always triggered on skr pro board

Hello kind people of the mpcnc world.
Just finished setting up my cncand i have encountered an issue with my endstops - they are always triggered.
I have an skr pro board with 5 2209 drivers ( i saw in the presentation you have 6…but we have 5 motors… ).

endstops are wired correctly and are working ( checked with my 3d printer )
drivers are working also
led on board is always red,with or without endstops plugged in
m119 returns always triggered, pressed or not

Any ideas that could help?
thank you

My first thought is that you wired your switches as normally open. The firmware expects normally closed switches. Run the M119 while you are pressing down on one of the switches. If the M119 says “open” you know you have them wired wrong. If the M119 does not change, and you are sure you wired them normally closed, you can test by shorting out the connection at any point starting at the board. You should be using the ‘s’ and ‘-’ pins, not the ‘+’ pins of the endstop plugs.

Note that the pins on most endstop switches are labeled C for common, NO for normally open, and NC for normally closed.

@robertbu Thanks for the reply
it appears that you were correct on the first assumption: once i checked with one pressed i got “open”.
the endstops are the ones from below image, with schematic attached.
makerbot_endstop
and then the question is: how do i wire them normally closed?

PS: these are the only switches i found with a roller and could grab at short notice. i forgot to buy when i was getting the parts for the cnc…

I know from posts on the forum, that a few people have tried getting these switches working as normally closed and failed. In one case, the person ended up de-soldering the switch from the board. Others just punt and buy new switches.

Another option is to change the firmware so that it expects the normally open switches. In configuration.h, you would edit all the ‘false’ to be ‘true’ in this block:

// Mechanical endstop with COM to ground and NC to Signal uses "false" here (most common setup).
#define X_MIN_ENDSTOP_INVERTING false // false // Set to true to invert the logic of the endstop.
#define Y_MIN_ENDSTOP_INVERTING false // false // Set to true to invert the logic of the endstop.
#define Z_MIN_ENDSTOP_INVERTING true // false // Set to true to invert the logic of the endstop.
#define I_MIN_ENDSTOP_INVERTING false // Set to true to invert the logic of the endstop.
#define J_MIN_ENDSTOP_INVERTING false // Set to true to invert the logic of the endstop.
#define K_MIN_ENDSTOP_INVERTING false // Set to true to invert the logic of the endstop.
#define X_MAX_ENDSTOP_INVERTING false // false // Set to true to invert the logic of the endstop.
#define Y_MAX_ENDSTOP_INVERTING false // false // Set to true to invert the logic of the endstop.
#define Z_MAX_ENDSTOP_INVERTING false // false // Set to true to invert the logic of the endstop.
#define I_MAX_ENDSTOP_INVERTING false // Set to true to invert the logic of the endstop.
#define J_MAX_ENDSTOP_INVERTING false // Set to true to invert the logic of the endstop.
#define K_MAX_ENDSTOP_INVERTING false // Set to true to invert the logic of the endstop.
#define Z_MIN_PROBE_ENDSTOP_INVERTING true // false // Set to true to invert the logic of the probe.

…then compile and reflash the firmware.

The benefit to having normally closed as the wiring solution is that if a wire gets knocked off, the stepper will just stop if you try to home. With normally open wiring, if a wire is knocked loose and you try to home, the stepper will continue to run until you shut the machine down.

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at least there is a solutions for it.
i would try to cut the pin of the NO connection, maybe this way i will interrupt the circuit on that part. not an expert here, maybe someone has some insight on this…
endstop with NO
until i will get better endstops i will try the software method and work with it carefully, if option 1 does not work
thanks for the help

I’m one of the people who ended up cutting the switch off the carrier board and soldering directly to the NC and C terminals. I could not find a way to tweak the wiring to get the board to work as NC. I think the problem is that the circuit uses the NC side of the circuit to carry voltage for the LED, since that’s a diode the current can’t flow the other direction, as would be the case if you just swap the NC for the NO connection. Since you lose the LED indicator in that use case, then I didn’t see a big benefit in keeping the circuit board at all.

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The issue with having normally open endstops is if you have a bad connection, when it homes, it’s going to crash.

@ttraband i have already set up the endstops with printed parts and wouldn’t want to mess it up.
Until i get better ones i will have to find a way. I will tinker with one of the existing endstops, and if nothing else works i will simply wire directly to the terminals.

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You can remove those switches from the pcb and use them by themselves. I think Robert already suggested that, but I wanted to point it out.

Otherwise, you need to edit the firmware.

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thank you everyone
i’ll try some of the options above and let you know how it goes. really appreciate all the help!

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tried with interrupting the NO connection - didn’t work
firmware change - worked
next steps would be to solder the connection directly to the switch itself

but ran into a different issue - homing towards the endstops. Mine goes the other way. I know there is a line in firmware which can change that, but i am yet to find it…

For the endstops, changing to NO probably isn’t a big deal. In the event of one becoming disconnected, it’s not good either way now.

X+ should move towards the right, and Y+ should move away from you. Home should move to left and towards you. Changing the home direction is a bad idea for various reasons. If your switches are the other direction, it’s better to move them.

Hey Guys,

im using the exact same end stops just wired Pin 4 and Pin 1 and everything works as a charm. default NC configuration. the led blinks when endstop is triggered. all validated with M119.

im using SKR 1.2 Pro with these makerbot design endstop boards without a issue.