Not trivially on most K40s, because of the custom ribbon cable on the K40. You can replace wiring all the way to the stepper motors, or use a board like the cohesion3d board that has the relatively unusual connector for the typical K40.
I removed the ribbon cable, put in mechanical endstops and wired the motor directly. Now it is like a 2 axis 3d printer.
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Does that mean that you figured out wiring? Or do you have specific questions about the wiring? Want to post a picture of what you’ve done so far?
It means that I haven’t figured out the PWM and L connections for the firmware… I THINK the
L to hotbed- and pwm to fan- . Is that correct?
I recommend letting the pot installed on the IN pin of the LPS (to set the maximum power) and only connect the bed - pin to the L pin (+ connect board GND to LPS GND).
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Claudio - did you mean LEAVING (= letting) (and what does LPS mean - laser power supply?)? Do you mean leave the IN pin as is and connect the L pin to bed (-)? If that is what you mean, you would be controlling the max power by the pot, and the Laser on/off by the L on bed (-)?
@Phil_Karza Yes, LPS is “laser power supply”
For the bed and motor +/- connections, the + connection is permanently connected to the input voltage (typically 12-24V), and the - connection is switched. They work essentially the same way. (The motor connection should have some extra protection in place that doesn’t matter here.)
The potentiometer has three connections. Here, I’ll give them names:
- Supply (positive voltage)
- Signal (middle post on potentiometer)
- Ground
(More generally, a potentiometer is a variable voltage divider which takes some voltage across the outside connections and presents an adjustable voltage between those two references on the middle, depending on where it is set.)
The middle “signal” connection on the potentiometer goes to the IN pin on the Laser Power Supply. This sets the power level. This only works if the other two legs of the potentiometer are connected to the right other connections. One side goes to 5V and the other to GND.
The pictures that @donkjr posted here might help you visualize this:
Then the L (fire laser when Low) pin is connected to the bed - connection on the board. (Bed or motor doesn’t matter much; both are controlled by MOSFET switches on the - pin, so this isn’t meaningfully different from the documentation you saw to connect to motor -). When the control board “wants” to fire the laser, it does so by turning on the MOSFET (switch) connecting the bed - pin to GND, which “pulls the L pin low” on the LPS, which tells the LPS to fire. It will fire with the power set by the potentiometer middle connector which is connected to the IN pin.
Connect GND on the LPS to GND on the control board.
@Phil_Karza Exactly what @mcdanlj wrote.
You can still controll the laser power from gcode (up to the maximum which is set by the pot). This is done by PWM modulation of the bed MOSFET (which grblLPC does when it gets S values in G1 commands).
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Thank you to both of you.
I think I will still leave the pot in circuit because from what I have been reading some of these tubes can’t take 100% - I have only been cutting at about 80-90% because of this.
do you agree?
We’re both suggesting that you want the potentiometer, so I think you are agreeing with us, not the other way around… 
We agree that you should not use 100%, even not 80-90%, because many K40 already reach the maximum tube current at 50-60%! To be save, you should add a analog amper meter (0-30mA) and never use more than 16-18mA.
Well, I got it working. I had to hook the L up to bed- and the IN to fan-. It wouldn’t work any other way.
The pot I set to about 50%- and the mA read 13 mA when set to 50% - of the 50% setting on the pot!
Sound about right?? Why did I have to connect IN to fan-?
That does not look right? You do not need the controller connected to the IN pin. It should only be controlled by the pot voltage.
Is there anything else connected to “IN”?
What is the bed and fan set to in the config.
[quote=“Phil_Karza, post:32, topic:80140”]
Actually, I tried without connecting anything to the IN. didn’t work until I did.
The IN must have something on it but in this case NOT the controller.
The LPS power is controlled by two signals:
IN: 0-5VDC = 0 to max power. This signal is usually provided by a potentiometer or in the case of the digital panel a PWM signal.
L: the L signal is usually connected to the controller’s PWM signal where it provides additional power control and beam ON-OFF.
Therefore the manually provided IN signal provides the max power and the L signal provides additional control from the controller.
This would be helpful:
- A picture or drawing of exactly how the LPS is wired.
- A picture of the connectors on your LPS.
- A picture of your control panel.
To test, you can connect the IN pin to the 5V pin and try it with the L connected to the bed.
This should work. Be careful as the laser will be operating at full power.
A post was split to a new topic: Can limit switches work during normal operation as well as when homing?
“”[Sep '20](Has anybody put grbl lpc on a mks sbase 1.3 - #31 by cprezzi
We agree that you should not use 100%, even not 80-90%, because many K40 already reach the maximum tube current at 50-60%! To be save, you should add a analog amper meter (0-30mA) and never use more than 16-18mA.""
Hello, noob here and I was just reading through some posts to get myself acquainted with the site and noticed one in this string where the user was running I think at 80/90% and you recommended that he run at 50/60%.
My system is all up and running, a K40 with MKS 1.3 board and GRBL LPC installed, I have been running my board which is on a analog K40 at about 6 milliamps and power 35% in lightburn and I find that works well for me cutting plywood in one pass, I am about to set up a 1 metre square bed for it not sure whether to go for 50 or 60 watt yet. I dont need tons of power just the bed space.
No one has ever been able to tell me whether I should increase the milliamps on the POT to the value you advised the other poster and lower the power in lightburn because of the higher milliamps or just leave it as it is at 6 milliamps and tinker with power in Lightburn?
I have to admit I was working on the “assumption” the lower the milliamps the more life in the tube.
I have no need for higher power unless it is advised to do it at a higher level and control it then by Lightburn.
Would you please be able to advise me on this. I just want to be sure I am running at the right MA.
Many thanks.
Neil Scott Sitges spain.
K40 analog, Makerbase MKS 1.3 Mac Mini Bootcamped to Windows 10, latest version, Mojave last version prior to Catalina running Lightburn latest version always.
The idea is not to exceed about 18ma beyond that there is the expectation that the tube life is shortened.
The combination of Lightburn and the pot to get the current setting doesn’t have a bearing on tube life … mA is mA no matter how it is derived.
Cutting at 6mA is pretty impressive especially plywood.
The below answer assumes your controller is controlling “L” and the pot is controlling “IN” on the LPS.
To some degree, the combination of settings (software+pot) is a personal preference.
The tube’s power will diminish over time. This means that for the same voltage from the LPS the tube will output fewer Watts.
So I like to set the software to the nominal power for the job. Then I used the pot to tweak the power to meet the needs of various variable conditions such as:
- Moisture content in materials
- Tube power reduction
- Variations in thickness
- etc.
This minimizes the changes you have to make to the job source due to tube and other variables that may change after the job is designed and tested.
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Claudio please what do you
What do you mean by X-Min Y min etc, are you talking about negative /ground on the board for the end switches in their relative sockets?
also is there anyway to reinstate the test button which no longer works
Im putting my laser K40 into a much bigger frame ( 1 metre sq) and would like to sort the end stops out properly and the test button if its possible on a mks board for now, later i will change over to a different board but funds dont permit that at the moment.
Im not sure wheter its possible or how to do it. thanks
By X-MIN, Y-MIN, Z-MIN I mean the crresponding connectors on the board because the firmware is preconfigured to use these ports.
I suggest to let the physical test and enable buttons on the K40 control pannel connected directly to the power supply, as original. This has nothing to do whith the controll board or the firmware.
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