Noisy PWM signal when laser is in motion (Ortur LM2)


I have little experience with engraving and have recently started playing with an Ortur Laser Master 2. I’m running into trouble with my laser power. Using the “Fire” command in the “Move” window, I am able to adjust the lasing power to my desired percentage via the “Power” control. This correctly sets the duty cycle of the PWM signal to the percent I have specified with a clean PWM signal (see attached image for clean PWM signal trace). However, when I want to run a path for the laser, the PWM signal is plagued with high noise and the underlying PWM signal gets lost in the noise and the laser begins lasing at varying power, but mostly just high power due to the relative amplitude of the noise (it lases at higher than the power I’ve set for each cut in the cuts/layers window, most likely because the signal is so noisy that the laser perceives a much higher duty cycle). This noise seems to be introduced to the PWM signal when the controller is sending motion signals to the motors. I’ve attached images of traces for the noisy PWM signal when the laser is in motion, the noise itself without a underlying PWM cycle that occurs when the laser is homing, and a clean PWM signal when using the “Fire” mode in the “Move” window. I have also attached images of my machine settings.

I’m not sure why the motion signals would have an effect on the PWM signal, maybe cross-talk due to weak insulation?

Any help would be much appreciated, thank you in advance!

This is fantastic. I wish more users had oscilloscopes!

This is one for @OrturTech as it’s solidly outside what LightBurn offers.

Are you measuring the PWM signal at the laser head or the board?
Where did you connect the ground clip for the Oscilloscope probe?

Thanks for the reply, John. I have disconnected the laser head and am scoping from the cable that connects the board to the laser head, so there is a possibility that there is some hardware issue occurring in the wiring downstream from the board. I will scope the board signal and see if the issue is originating there.

I’m grounding on the PWM-

Sound to me like you have a ground reference issue
The best way to probe, to avoid any wiring interferance of bad contact would be on the motherboard itself

However if you follow the cable along
Remove connection from top motherboard
Top and bottom of the PInboard. All pins look healthy?

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You also should add termination to the line since you don’t have it connected to the laser (If I read correctly).

A 10k resistor should work.

Thank you John, Gil, and Brewster. Apologies for the late reply and thank you for your patience. I’ve probed the signal at the board and at each connection between cables (all pins are healthy and clean btw) and have found that the noise must be introduced somewhere in the cable connecting directly to the motherboard. The PWM coming directly from the board was clean and accurate for different powers, and after the cable, the signal is noisy. As for what exactly in the cable may be introducing this noise, I am still unsure. Weak insulation or perhaps a wire was broken somewhere in the line due to movement/manipulation of the cable. More testing is needed, but the solution may just end up being a cable replacement unless I have missed something.

a microfracture on the wiring is what makes more sense, if its within the cable itself will be nearly impossible to diagnose acruatly. but if the signal leaves the motherboard Clean, then is induced along the way.
Will get to your ticket, a cable set is in order

Sounds reasonable to me. Thanks for the help Gil!

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