So I have a NEJE 20W Engraving Module laser coming today. I have messed around with lasers on an ender 3 but it was one made for it. I have an SKR 1.4 Turbo board. My mpcnc works great with the current setup using a marker but wanted to attach the laser module. Just wondering how I should go about controlling it and what pins should I use on the skr for it. I have read us the fan header. Has anyone done this if so how did you go about it.
I’ve currently got that laser module running on my rolling-gantry FoamRipper2 machine. I’m not overly impressed with it – I can do pretty much the same job with my 2.5W Eleksmaker/Banggood units – but it does work. I do like the form factor and the build quality seems pretty good…
Unfortunately I can’t be of help with the SKR hookup (I don’t have one…) and I use/prefer Grbl 1.1h for my laser control. However, the 2nd photo above shows the laser module wiring (see CAUTION below). There are 4 wires… but the green one (a temperature pin) is unused. The red and black wires are +12V and GND respectively… and the yellow is the PWM control for intensity. Here I’ve used simple +5V PWM from the Eleksmaker 3-axis board in the background which provides a very convenient 3-pin port for the laser power and PWM.
CAUTION: I found the supplied laser cable color coding bass-ackward (left-to-right vs right-to-left) on the unit I received. In the photos above, I have re-ordered the wires to use a more conventional red and black for +POWER and GND, respectively… yellow for PWM, and green for TEMPERATURE/C. While the wires don’t really care what color they are… it might well confuse you if you aren’t sure of what wire is carrying what… 
For your case, I’d connect the red and black wires to the same +12V that powers your SKR board and the yellow PWM intensity control to the M106/M107 controlled FAN pin… either remapped to a +5V PWM pin, or – if you’re courageous! – directly to the +12V FAN control pins. [If it were me, I’d remap it to a +5V PWM pin.] Chances are the +12V FAN pins are low-side (GND) switched (giving an inverted PWM output) and you’ll be testing the truthfulness of the laser vendor’s spec on the 3.3V-12V PWM control input.
Good luck!
– David
hey, thanks for the help
so you don’t use the included board just wire the 12v red black to power and the yellow to a PWM header on the board? I wish I didn’t use the skr 1.4 board figuring out all the pins is a pain. still need to see which pin on the board is 5v PWM have no clue lol
No, the little Neje interface board isn’t necessary. You can go straight from the controller to the laser module… you just need +12V, GND, and the PWM signal and all are available on the controller.
Since the SKR board has become popular here on the forum and there’s been a lot of discussion of use with laser and Marlin, I’m sure someone here can tell you which pin can be used to get a +5V PWM signal from… 
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thank you
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I know this is a few months old now but did you get this working?
Also interested, I’m not sure if MOSFET is blown or what, but I used the precompiled firmware for SKR 1.4 Turbo and TMC2209’s, precompiled TFT firmware also, and M106 does nothing. I’m using a regular fan on p2_03 and its just on 100% all the time, even if I hit the reset button it stays on. That and the fact that so many other people are saying their MOSFET has blown for those pins makes me think it may be bad. But if anyone can help I’d really appreciate it. I did have the board operating a printer before this and the print fan did go bad, and also the new fans I ordered had the + and - wired opposite the way the connector on the board was expecting so I haven’t exactly been super kind to the MOSFET. If anybody knows a workaround I’d really like to get this laser going. Its the 2 wire type, 12v 0.5A like the ones Creality sells. It comes on like the fan but there is no modulation when I send commands, its just on all the time.
This link may help
laserweb.yurl.ch/documentation/initial-configuration/65-grbl-lpc-1-1e
Thanks I’ll check it out. In the meantime I just swapped p2_03 with p2_04 and cut the connector off the laser wire and it’s working fine now but I really hate it when stuff doesn’t work the way it is supposed to so I’d like to fix it at some point