Wiring a skr v1.4 turbo into a k40

Hi there,
I am looking to install a skr v1.4 into my k40 but i am just getting a bit stuck with the wiring .I have read the skr v1.3 write up that is on this forum but because they use a different type of psu than mine its just throwing me off lol.
The psu i have is the one with the jst connectors

Now am i correct in thinking is all i need to do is connect the L wire on the far left to a pmw pin on the skr i.e pin 2.3 which is the fan - .
The 24v is coming from a separate power supply and i just disconnect the 5v and leave disconnected.
Also i flashed the cohesion smoothieware firmware.bin to the skr and since doing that the board wont show up on my macbook ,does anybody know why this might be please.
Any help is gratefully appreciated thank you Nutbox


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Thank you ,that is the thread I have been reading but because the psu is different it has confused me lol.
My psu only has the L pin and no laser fire or laser pwm but would the “IN” be where I connect the skr pwm pi to and laser fire to the L pin?
Hope that makes sense cheers

Although I have an interest in the K40 types, I’m not any kind of information source. Try over here…

if you don’t get much from here. I know many of ‘those’ come over here (and vice versa) good bunch.

This isn’t exactly your problem, but any power supply connections might give you what’s needed to make it work.


No worries buddy thank you for your help,

For some reason I keep thinking the K+/K- is the control input. Generally they have an L input, which is usually a type of ‘laser enable’ and the PWM control, IN to turn it on and off.

Now you got me curious…


Maybe if you clued us in the the type of supply you have. It has got to be documented somewhere…


I have seen cohesion board just uses the L pin and the controls the laser max limit with the k40s potentiometer and then I see in the write up you link that the lasers min and max power is software controlled so that’s where getting confused.

I thought the SKR V1.4 was your new controller?

If the controller supports it, you can set your max and min power levels and let the controller handle the cornering…

Don’t worry about max and min, just get it up and you can worry about details like that later. In all probability, it’s up to what control board you have.


This is my psu

Yes the skr is the board I have I was just using the cohesion board as a example

Looks like the L pin is the return from the tube, where the ma meter might go.

The PWM goes to the IN connection of P2.

‘laser fire’ is the enable and it’s shown going through the voltage level translator. I would think you would use the L pin of P3 to enable the laser. And let the PWM control it.

The 5v is an output voltage, so you don’t connect to this unless you have a low current <50 ma 5v need. Such as the level translator…


Hi Jack,
I have got the skr moving the axis in the right direction and homing all good so now on to firing the laser.
Is it my understanding that as you have stated above is that the pwm wire should be connected to the IN pin on P2 and then the 5v from the logic level converter should connect to the L pin on P3 and the laser should work like the thread you linked me to and from this diagram

If you get what i mean?
Thank you for all your help its much appreciated Dazz

Don’t say that around the airport… :crazy_face:

I’m just reading the diagrams. I understand how most of these work, but there’s seems always to be some kind of exception.

If you notice the K+ enables laser at a low level, L enables laser at a high level. On my supply, the H has the same operation as the K+ in that it’s the ‘inverted’ enable, so to speak. At least that’s my interpretation.

More like the 5v side of the converter, yes.

Apparently the signal coming out of your board is on a 3.3v system. I would think if you don’t need that converter for your pwm, you wouldn’t need it for the logic level of the ‘Laser Fire’ either, IMHO. Maybe someone can clarify.

Don’t know how much power and where you have it available, but I would think the level converter would require a very small amount of current and you could probably run it off the supplies 5v tap. It’s limited to 50ma.

Good luck, take care.


ok i read some more of the post you linked me to and see squid is using just one wire which is pwm controlled so i thought i would try that but when i check the voltage coming from the skr pin it is around 20v i have tried inverting it ,pulling it down and open drain with not much change in output,i thought these pin were suppose to be 3.3v as you say?
thanks again

There would be no point of a voltage translator circuit if that were the case, I would think.

Is this the PWM output of the new board?

It’s normally 5v ttl levels, but more boards are using 3.3v systems. I will have to further look at that board and see what’s happening.

I don’t think you want 20volts applied to any part of the control system.


Thank you for your help I know little about lasers so have dived in deep lol but I have mess with skr boards on 3d printers.

right more playing about today found another write up on installing the skr v1.4 into the k40 and it used one wire for the pwm signal to the L pin in P3 on the psu copied their config file and nothing tried numerous configs but then had a epiphany and added a ground pin next to the pwm pin i was using and connected it to the chassis and the laser fired up,so is this the solution?
Here is the diagram of how it wired up minus the ground which is connected to the ground pin of the neopixel connector.

Cheers Dazz

Success is in the results. If it works then It’s probably ok. I was suspicious that the K- was related.

If you use separate supplies that interconnect, they must have a common way for the return currrent or ground.

Sounds like you are up?


From what I can gather is k- is supposed to be the same as L on P3 .
The thing that confused me is I thought the ground of the skr that’s attached with the 24v power to the board should of taken care 9f the grounding shouldn’t it?