Alternate PWM Output Usage?

Machine: Custom 6030 build

Board: Laserboard

Firmware: Smoothie

Power supply: Cloudray HY-T60 Plus 60W

Laser Tube: TEN-HIGH “60W” 1000mm/50mm diameter

External Stepper Drivers: Stepperonline DM542T

Problem/ Question: Any problem with using the 0-5v out from the Alternate PWM pins?

Motion is working great, started on wiring the LPSU. (Not currently hooked up until I have satisfied my understanding of the whole system)

I understand the typical method is to wire 5V and a pot to the IN on the LPSU to set the max current of the laser.
The Laser fire wired to the TL uses a duty cycle to turn the laser on and off rapidly to simulate power control.

Essentially, the TL is laser on/off, using PWM sort of fakes a power level for the beam.
The IN on the LPSU is a true power level driven directly by 0-5V.

Using my multi meter to check the Alternate PWM pins I notice it scales 0-5V nicely based on the power level of the cut settings.

My thought was why not wire those connectors to the IN and G on the LPSU, also with a pot to control max power?

In theory this would allow proper grayscale laser control, and allow power control to engrave and cut sending all operations for a job in order. No need to set the power level for engraving on the pot, run the operation and then set power for cutting and run the next operations.

I did check to see if there was a common ground on the Alternate PWM output pins. It looks like they share ground with the USB connection only. The ground for the stepper drivers, machine frame and the Laser connector pins are isolated.

So, would there be an issue using these pins and the grounding differential?
What are the use cases for the Alternate PWM pins, I haven’t seen any references on the forum or documentation.

Worst case I think I could use an op amp as a voltage follower to read the Alternate PWM output and isolate it safely to the IN/G on the LPSU.


You can bypass a pot by connecting IN to 5V on the LPSU with a wire jumper and continue to use TL as we intend. Alternate PWM Out on the LaserBoard was indeed meant for several use cases including this one and also laser diodes that take a 5v TTL input, but I prefer the L way for a multitude of reasons. If it doesn’t work out for you then we can discuss the alternate way.

Understood, I am intending on having a pot in the mix regardless to limit max current.

What I am hoping for is the ability to have power level controlled dots like how Russ Sadler’s demos show.

With TL turning the laser on and off based on duty cycle, you get dots at whatever the pot limits the laser power to. 80% power dots for engraving so that the following cut operation has enough strength to make it through the material.

With the power level controlled by the Alternate PWM voltage you get variable power dots during engraving and then 80% cut power all based on the power level settings you define in Lightburn.

This is where a DSP controller like a Ruida shines I guess. Just hoping to make the most of the Laserboard I bought only a few months ago and not have to sell it to buy a DSP controller.

A Ruida does control both TL and IN, yes. There is no pot in the mix. It should be possible to set this up on the LaserBoard running Smoothie.

However, it’s a lot easier if you just try it my way first. The way I suggested (pot to Gnd, IN, 5v on the LPSU and TL and Gnd to Laser Fire and Laser Gnd on the C3D LaserBoard) works well on thousands of machines powered by C3D in the wild.

This Laserboard was previously install in a K40 and working well, such a simple plug and play process :slight_smile:

Building my own custom machine was the next step.

Thanks for the details and input!