Cohesion3D Mini PWM for LaserTree 80W Diode Laser

Machine: K40

Board: Cohesion3D Mini

Firmware: GRBL-LPC

Problem/ Question: I’m looking to change my K40 laser cutter from CO2 to diode. Steppers, end stops, and everything else is working just fine. I have power running to the laser diode. The only problem I have is knowing where to connect PWM on the Cohesion3D Mini board to drive the diode laser. Do I need to change some config to enable PWM on one of the pinouts?

Link to the laser I’m trying to use:

Link to Cohesion3D Mini Wiring Diagram:

I’ve tried just about every pin I could think of to get a PWM output from this board and I can’t find anything suitable. I’ve also tried changing the GRBL config on the SD card to various pins while using an oscilloscope with GND as a reference, but I can’t find anything that produced what might be a valid signal. See the attached photo for more info.

I do see something small when I connect to the Laser-On wire that would originally connect to the K40 LSU, but it looks like the voltage is tiny. Is there a connection I’m missing to increase that voltage? Is this driven by the Mosfet Vin?

Is this board not compatible with Diode based Lasers? I see other people having success with the newer LaserBoard, but I haven’t found much with the Cohesion3D Mini.

I realized my problem. I was confusing the config file for the old firmware (Smoothie) and the GRBL config. The changes I was making had no impact on the board because I was not using Smoothie.

Changes to the PWM pin for GRBL would require a recompile of the firmware (from my understanding).

The fix that worked for me was to revert back to Smoothie firmware for the Mini and change the PWM pin to 2.4.

This is the firmware I used:

Referenced from here:

My PWM pin needed to be inverted (laser activates on HIGH) so my Smoothie config line was:
laser_module_pin 2.4!

The exclamation mark inverts the PWM signal.

My diode laser is now firing properly using PWM from the Cohesion3D Mini.

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