Limit switch wiring question..

I purchased some inexpensive limit switches without identifying their status as to NO or NC so I'm trying to understand how to tell the difference?





While wiring up my DuetWifi I assumed the switches were NC switches but to my surprise they appear to be NO or did I mis-wire something?

The DuetWifi board has a green light for the +3.3v as can be seen in the image below and I think that is a good sign.



and from a wiring perspective I thought I wired them correctly, red = 3.3, black=gnd, green=signal.

Can someone explain how the word "pulls" is being used in the descriptions?

Endstop switch pulls signal from GND to +3.3v when triggered - Active High/NC

Endstop switch pulls signal from +3.3v to GND when triggered - Active Low/NO

Did I make a mistake in wiring them or are they NO switches?

If they are NO, can I reverse them to be NC by switching the BLACK and RED lines?

Thanks.

Those are not simple NO or NC microswitches. See "Makerbot mechanical endstop" in the Duet3D wiki page on connecting endstop switches.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I am almost certainly wrong but... in the description there:

Endstop switch pulls signal from GND to +3.3v when triggered - Active High/NC

Endstop switch pulls signal from +3.3v to GND when triggered - Active Low/NO

Aren't the designations NC and NO here the wrong way around. A Normally Open switch reads 0v open and 3.3v closed and is active high. A normally closed switch reads 3.3v open and 0v closed and therefore is active low. NC fails-safe as a wire break causes the controller to read 0v, and stop rather than crash the axis.

Edited 2 time(s). Last edit at 11/16/2017 07:19PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

I am using one of these switches on my 3D Printer.
As the end stop board has a hardware 10K pull-up resistor added with the internal 4,7K pull-up you may want to disable pull-ups while using end-stop board.
I skipped this step as the current was not so high as to cause problems. If you have a limited supply you may want to enable individual end-stop pull-up resistors.

I have it coded as follows
#define X_MAX_ENDSTOP_INVERTING false // set to true to invert the logic of the endstop.

All other Endsotps are coded as follows
#define X_MIN_ENDSTOP_INVERTING true // set to true to invert the logic of the endstop.
#define Y_MIN_ENDSTOP_INVERTING true // set to true to invert the logic of the endstop.

using a proximity sensor for Z
#define Z_MIN_ENDSTOP_INVERTING false // set to true to invert the logic of the endstop.

Hope this helps

Edited 1 time(s). Last edit at 11/16/2017 08:45PM by Roberts_Clif.

Thanks DC42 for pointing me to the correct wiring.

Will re-wiring the switch effectively operate it as a NC switch which I understand is the better approach?

DjDemonD, that's what I'm seeing on the configuration tool description..

Edited 1 time(s). Last edit at 11/16/2017 08:45PM by ampapa.

When I've used these endstop boards on the past it has annoyed me that they work NO/active high and therefore have no failsafe mode. It sounds silly but it's easier to cut the switch off the pcb and just wire it from pin 1 to pin 3 which is a NC circuit.

Edited 1 time(s). Last edit at 11/17/2017 02:06AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
I am almost certainly wrong but... in the description there:

Endstop switch pulls signal from GND to +3.3v when triggered - Active High/NC

Endstop switch pulls signal from +3.3v to GND when triggered - Active Low/NO

Aren't the designations NC and NO here the wrong way around. A Normally Open switch reads 0v open and 3.3v closed and is active high. A normally closed switch reads 3.3v open and 0v closed and therefore is active low. NC fails-safe as a wire break causes the controller to read 0v, and stop rather than crash the axis.

The description is correct, because a microswitch with a 2-wire connection to the electronics pulls the input to 0V when it is closed, and the pullup resistor pulls the input to +3.3V when the switch is open.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].