Limit switches disconnects the laser. I hope you can help

Hi, hope you’re all well?
I have a Sculpfun S9 and have finally got round to installing limit switches on the X,Y.

Everything seemed to go well until I homed the laser. Once the gantry touches either of the limit switches the laser gets disconnected from the laptop.
I thought the rebound wasn’t set. But it it, it just doesn’t seem to work.
I have rebound set to 5mm but if the the laser disconnects once the switch is hit how can it rebound?

Any help would be greatly appreciated. This is confusing me.

I don’t know how your limit switches need to be configured.

There a two ways, with the switch pulling the controllers input low and via a configuration change you pull it high.

The most common is pulling it low.

Does it reset or ? when it hits the limit switch. Disconnecting isn’t very descriptive.

What happens if you manually activate one of the switches by hand.?
Disconnect or reset?

Do you have a schematic or some blog you followed installing these? That may help me understand how it’s supposed to work.


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Thanks for the reply, I say disconnects because it disconnects from Windows and Lightburn, I get a notification from Windows, like you do when a USB plug is pulled out. If I then manually pull the gantry away from the switch, so it isn’t pressed in, Lightburn see’s it again and reconnects.

The switches I have used where recommended because they didn’t need to be rewired.

I read this thread, it’s pretty lengthy.

If I get chance tomorrow I will head back to the workshop and record a short video.

What I’m trying to find out is how the laser and board (controller) reacts when you press one of the switches. I understand it’s like pulling out the usb from the PCs viewpoint…

If that switch isn’t wired right or ‘flipped’ in the connector, you could be shorting your power to ground. This would reset the controller… They look ‘keyed’. It would be tough to get them in backwards.

It’s three prong connector, looks like it’s Signal, Ground and Vcc. You have all three of them and the switch should just connect S to G.

They are two wire, like in the link ?..

Make sense?


With everything plugged in and turned on test the voltage between V & G with a volt meter then apply the limit switch. If the switches were soldered to the limit switch board upside-down a short circuit could be created. Shorting Power to Ground on a USB device would drop the voltage to zero or near zero. Because the USB supplied power is likely current-limited and protected by your computer it seems to recover… so far…

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My sincere apologies for coming back to this so late.
I am still struggling with this, I thought by just snipping the wire connected to V is would resolve the issue. And while it has, as is when the switch is activated it still turns off the USB but the gantry does bounce back. However it only does that for the switch it reaches first (closest).

I’m probably going to try other switches as other people seem to have way more success.

And now I feel I have the wrong switches. When I looked at my Amazon order the switch listed are not the ones I received.

Thank you for your help.

Do you have a voltmeter…? They are cheap and they can see what you can’t, like how your switches are working.

The link ‘promised’ to add the switches (at a latter date), but I never saw anywhere on how they are connected to the machine. How/where did you connect these switches ?

Have limits on all my machines, save 1, they are simple and I think you are getting frustrated because you don’t really understand how they work. Without knowing how they work you are kind of dead in the water when it comes to fixing it.

Let us know what we can do to help… I don’t think you should take things apart and try other switches until you confirm the culprit. Don’t chase your tail, you will become more frustrated.