I have Sainsmart Mechanical End Stops, and I'm building a Prusa i3 Rework.

I've recently gotten the x-axis to move, but it needs to stop when it gets to the end and it does not do that; I end up having to pull the plug.

From what I understand, there are two ways to wire ends stops in general, but you have to change the settings in the firmware to make it work right.

There are 3 connectors on the board:

  • S (signal)
  • - (ground)
  • + (VCC)

My Sainsmart Mechanical End Stops have 4 connectors!!!

According to their website, left to right with the white connector facing you, they are as follows:

enter image description here

  1. S
  2. Normally Closed (NC)
  3. Normally Open (NO)
  4. VCC

Now it seems to me that if I take those connections and connect them as follows it should work...(ramps on the left, sainsmart end stop on the right):

  1. S (signal) -> S
  2. - (ground) -> Normally Open (NO)
  3. + (VCC) -> VCC
  4. nothing -> Normally Closed (NC)

...but! Screwing this up by either using the wrong firmware of selecting the wrong wire frys your board, so I thought I'd ask here. Sources please.

  • $\begingroup$ The picture shows "S, GND, GND, VCC" but you list "S, NC, NO, VCC" in your post. I think the picture is correct, as indicated in my answer. $\endgroup$ Commented Jul 7, 2016 at 18:57

1 Answer 1


The multiple connections are redundant. Your picture indicates the wires labelled as "SIGNAL, GND, GND, VCC". This is correct if the board is a "standard" mechanical endstop v1.2. The two middle pins are both ground, but you only need to use one of them.

You can simply connect signal to signal and ground to ground. That is sufficient for the endstop to work. You only need to connect VVC to VVC if you want the LED that's on the board to function.

  • 1
    $\begingroup$ I can add as a source: My printer works with the connections as shown in your picture. (I had to learn it the hard way due to all the confusing information on the internet) ;) $\endgroup$
    – kamuro
    Commented Jul 9, 2016 at 9:41
  • $\begingroup$ @TomvanderZanden Tried this last night, and board did not fry for the x-axis! Thank you! $\endgroup$
    – leeand00
    Commented Jul 20, 2016 at 12:56

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