So I have some concerns about your proposed setup, but I don’t have the knowledge, or technical details of the SKR Pro board, or knowledge of your setup, to know if my concerns are warranted. So this post is musings to consider rather than well founded information.
If the laser module is really 40W, then you will be pulling 3+ amps. If you purchased a kit from Ryan or are using a similarly spec’d power supply, it won’t provide enough current to run both the laser and the steppers.
I have only a vague idea of how multiple busses are handled on these control boards, but are you sure the fan pins are on a bus spec’s to handle higher current? If you want to pull current from the board, wouldn’t it be safer to use heater pins? For powering the laser (enable), you don’t need a PWM pin.
When using a laser, speed is beneficial to have raster operations complete in better times. One way of potentially improving speed on the LowRider would be to run the steppers at 24V rather than 12V. If you use board pins to power the laser, you’d have to move to a separate power solution for the laser.
I’m not sure what you are getting by using PF9 (vs. PC9) for PWM control of the laser. The laser control board will handle 3.3V - 12V and I doubt it draws much current, so I don’t see the need for PF9. In addition, I read that on some of the CNC control boards, higher voltage pins use ground-side switching to generate the PWM, and that has caused problems using those pins to drive lasers. I don’t know if this is true for the SKR Pro.
So in this thread it sounds like he just has the 12v and ground hooked up to FAN 0. Maybe I understood that wrong.
And then it sounds like @mperino has PC9 as PWM for the laser and PF9 attached to a relay to turn the laser on and off.
So my thought was trying to combine all of that have everything plugged up to the SKR pro without having to use an additional power supply and that little control board, mostly because I’m trying to avoid unnecessary clutter. I’m probably overthinking things though. I tend to do that xD
I wasn’t thinking about it pulling too much power, mostly because that other thread sounded like he’s pulling 12v to power the laser off of the board, but after thinking about it, I think he might have it set up differently than what I initially read it as. So you probably stopped me from shorting something out
Edit: Also, I had a typo and said PF9 instead of PC9 in my previous post
Like you I wanted to isolate the power pull from the Laser so it’s not being drawn through the board. I use an SSR (Solid State Relay) to switch the power directly from the Power Supply using the SKR as the Control. I bought mine 2 for $10 for another project, but I see equivalent ones for $8-10 for one these days.
It was just a quick and dirty bracket where the control board is hot glued to the bracket. But for what it is worth, I’ve attached a ZIP file. I included the STEP file as well as the STL.
Edit: Fixed model. LaserBoardMountBracket.zip (28.5 KB)
