UPDATE: PWM is working!! but cuts have been effected.

UPDATE: PWM is working!! but cuts have been effected.

Hi, I have a K40 laser and im doing the smoothieboard upgrade using MKS sbase 1.3 board with the MKS tft. I have all mechanical parts working includind endstops, home is working correctly.

I am having trouble with the pwming on the laser. I am trying to follow some of the guides here but not sure which wire to connect to 2.4 on my board. do I use the IN or the L in Dons guide he suggest using L but when I do that everytime I move the laser fires. some other guides suggest using IN…

Any help would be appreciated.



Yeah, using an MKS base is not going to win you any friends sorry. They doa closed source smoothie and offer no sorr support not give back to the community.

@Richard_Vowles I know I am trying to purchase a real smoothie but cant get one here. I am going to donate to Don and Wolfman for all the great work they do.

Your objection and stance might be appropriate if he posted in the Smoothieware support, but I don’t see any issue with him asking a hookup/wiring question here.

Hi @Kelly_Burns just looked at some of your projects and they are amazing! I also seen you have made your machine full width, I will be doing that upgrade once I have all the new electronics working correctly. Did you use makerslide?

Yeah, I did both the physical and electronics upgrade at the same time and under a deadline for customer projects. It was painful. In my rush, I actually fried a Genuine Smoothie board with a stupidity.

I will be publishing a complete write-up for both electronics and physical upgrades. All my stuff is leveraged off the great work of +DonKleinschnitz, @Ariel_Yahni_UniKpty and others.

Look at the @raykholo 's Cohesion board. I believe it’s a Smoothie community approved setup and the Mini is a drop-in replacement for the K40 controllers. Its also priced just a little bit more than the hated MKS sBase. Ray also provides great support in the community.

Here’s the hookup I had when I had the MKS sBase in mine. (-) pin of 2.4 (FAN) going to L on the PS. PWM Frequency should be 200-400 (not 20 as documented in a few places) I can’t remember where I left off with that, but I know 200 gave me a decent start I PWM laser power control.

Hi Kelly thank you for comments…

@donkjr , @Ariel_Yahni_UniKpty are brilliant and without the information that they have published I would not be any where near where im at now.

I will look into the cohesion board an might use the MKS on my 3D printer.

I have my L going to that pin also but when I move any axis the laser turns on??

Here’s that link: http://cohesion3d.com/cohesion3d-mini-laser-upgrade-bundle/

thanks @raykholo looks awesome… have to save my pennies now!!

The L input is switching the laser psu on/off. The in is the pwm input of the laser. Don had an experiment where he used the L as pwm and the in fixed to 5v. Both methods work. Cheers

@Ben_Myers it looks like you have read the blog posts on this subject so I will not link it here.

The L pin connection schema works fine if all of configuration and such is set up right including the polarity of the signal.

Please post:
…Picture of your power supply (the input pin side)
…Picture of your connections between the MKS and the LPS
… Picture of your control panel
…Your configuration file

If I recall right @Jorge_Robles1 was using a MKS you might try an connect with him. I generally do not post info on MKS because the do not cooperate with the smoothie community. However I do help everyone …

If you can you point me to a schematic of the board you are using I will look at it for you.

Have you verified that your LPS is working correctly.

  1. Push the test switch on down on the supply does it fire?
  2. Disconnect anything that is connected to L of the LPS.
  3. With interlocks enabled and the “Laser Switch” ON, ground the L pin on the LPS, does it fire?

Generally from the symptoms it sounds like something is grounding the L pin. Which suggests something in the config file.

@Paul_de_Groot thanks, im unsure what you mean. I have it hooked up the L but it seems to be firing with no pwm? just full power up to the max set on the pot.

@donkjr Hi Don thanks for your reply and thank you for all your work on the K40… I have attached the pictures and config files as requested.

Connecting are as follows as per above first posted picture. (no change is original wiring)

High Power
(as per above, no changes)

G -> laser on switch (no change)
P -> laser on switch (no change)
L -> Fire Switch (no change)
G -> no change
IN -> 2.6 negative terminal (blue wire)
5v -> no change

Low Power
24v -> 12-24 input positive terminal
GND -> 12-24 input negative terminal
5v -> not connected
L -> 2.4 negative terminal (brown wire)

with it setup like this the laser turns on and off as expected but the power level when set as low as s0.3 in the gcode runs at 20ma and wont even cut through 3mm mdf when with the M2 nano it would cut the mdf at about 11ma. (test gcode below)

G21 ; All units in mm
G28 ; home all

G00 X2.762953 Y240.677863 F6000
M3 S0.3
G01 X132.762873 Y240.677863 F400

Using the M2 nano board everything worked correctly.

I really appreciate your assistance and when I can afford to I will be purchasing a real smoothieboard and donating you some money.

I think I’m rambling a bit here. let me know if I need to clarify anything. Thanks again


Couldnt find an actual schematic. hope this will suffice.

are you saying that you have a configuration that works but the power is to low as set from Gcode?

“with it setup like this the laser turns on and off as expected but the power level when set as low as s0.3 in the gcode runs at 20ma and wont even cut through 3mm mdf when with the M2 nano it would cut the mdf at about 11ma. (test gcode below)”

@Ben_Myers it seems you used the extruder E2 pin from the board to drive the pwm input IN. Maybe you need to configure smoothie to use E2 as laser pwm port?