Got my unit running on 1.23 for PWM and 2.5 for enable (MKS SBase

Especially since smothieware is doing power /acceleration calcs.

are you using + or - on p2.5?

  • pin. The + pin is tied to 24v+

@Jon_Bruno Right. The + pin is 24v. I get 0 on the - pin which is what we’re using. So how is that dangerous and why do I need to remove the LED? I got my multimeter out and at no time, firing or idle do I see 24v on that - pin or the L pin I’m connecting to on the LPS. Also, the whole pin inversion thing is confusing to me. I currently have the pin inverted in my config. Laser firing and PWM both work great…

I’m driving right now so I can’t really give you much detail but check that pin and reference against chassis ground or simply touch the ethernet connector Shield and do a voltage readng between the shield and that PIN

As for the inversion of the pin take a look at your controller right now if the unit is Idle that green light should be off if it is on the laser is enabled and that is not what you want

@Jon_Bruno Yeah. That’s how I took the measurement. I have +24v on the + pin and 0v on the - pin. I’m using a Fluke multimeter, if I check all the other screw headers (heater1, heater2 and fan…I dont have the pin numbers in front of me), they’re +24v on the + pin and +22v on the -.

I’m active low though which means I want it off to fire, so I do want inversion. jesus I need to go to school for this crap.

@Jon_Bruno , @StephaneBUISSON was the one who had the PWM and POT together in their K40 Here is a link to his schematic:

Anthony, I’m not sure why you would want that pot in the mix though. It can be done, but then your PMW would be kinda worthless.

For on the fly power adjustments if the setting you set in the gcode is not optimum

@funinthefalls Personally, I would start over. Adjust the gcode and run again.

He’s not doing pwm on his power setting in that schematic.

There is a grey area of info out there between the 1 and 2 wire setups.

As I understand it,

The 1 wire config uses pwm to modulate the actual Laser firing while maintaining the stock pot for max mA setting. In other words the duty cycle of the laser tube is controlled by the pwm signal while the max output power is constant.

With the 2 wire setup there is an enable pin involved as well.
The enable pin arms and disarms the laser firing but the actual power to the tube is modulated via PWM.
In other words the laser is turned on and then the power is adjusted with pwm to desired levels during the burn.
At least that’s how I understand it works between the two.

The diagram you linked is a 1 wire setup

@Alex_Hodge the pot act as ceiling (to set max mA , to preserve the tube life) I barely use it at all, the cutting setup is software made. (well my K40 is on the road for one month, so no assistance at the moment)

That is a very good reason to keep it. Thanks for clarifying that for us Stephane.

I set my max laser power to 0.8 in the smoothie config file to make sure I don’t overdrive my tube.

I am using a 2-wire setup but my laser fire wire is tied to GND permanently. My PWM wire actually turns the beam on or off as well as sets it’s power level.

I do not have a POT in the circuit.

I DO still have the interlock button on the panel and I make sure to turn the button off before I open the cover, just in case. but my SBASE / LaserWeb setup works perfectly and I have had a lot of success in multiple jobs ran with it so far.

However I did find that my SBASE does not have a 5V output, it’s actually outputting 4.7V so I may be having max power issues, but since I limited max power to 0.8 I am not quite sure what effect the 4.7V actually has.

@Alex_Hodge Just reviewing my posts… I thought I had better answer you …
The 24v potential is on the LED, that potential is therefore available at the lpsu Enable/Active/Fire! pin. This input pin typically connects to an opto-isolator or a simple transistor before going into a PWM IC or other triggering circutry. What we are doing by not removing D14 is leaving a 24V+ potential on the cathode of the Opto and while there is 5V+ on the anode if the diode or if a transistor the junction should break down there could be some substantial down stream damage to anything on the 5v rail

I realize this is quite an old post however would any of you be willing to share your pinouts as well as your config file. I’m struggling with getting any PWM signal at the moment. I either have thing wire wrong (I don’t think I do) or my board simply isn’t working as it should. I’ve tried the PWM pin out from 1.23, 2.5 and scoped other pins without luck. At this point I don’t care if I have the pot ceiling installed or not. Whatever way I can get to simply work is fine for me. I can always refine it later.

Thanks in advance if you can help.

Hey Chuck…
Sadly you, much like myself took what we thought was the easy way out.
I bought an MKS board assuming it was a cheaper alternative to an actual smoothie board ( truth be told, they were out of stock)… I was wrong, at least when the expense of time is factored in.
I did have some success with PWM by using the two wire setup (one for Laser Enable(pin 2.5^) and one for PWM power level(pin 1.23)) and a level shifter board. the setup was more of a headache than I was willing to struggle with any longer.
Endstops weren’t properly working, pwm functionality was flaky at best and firmware updates that people were pushing out did not properly apply to this board. I shitcanned the idea of using this for laser work… It’ll probably be great for a polargraph or some other cartesian device but in this configuration with this particular hardware it was a battle every step of the way.
Perhaps others will chime in with advice or solutions to your issue, I however have nothing but bad things to say about this board and I’m sorry that you are finding it difficult to configure.
Bottom line, It’s a big fat steaming piece of garbage.
If you search on my posts I’m sure I shared my findings along the way, perhaps they will prove useful to you.
The config file I was running can be found at:

best of luck.