@droftarts said in Heater 3 Output when in Laser mode:

I don’t know why you are getting a blip at power on. I don’t think the heater output goes high at startup. Possibly it is your circuit that goes high before coming under the control of the heater3 pin. Alternatively, you could bring the laser PSU under the control of the Duet, and only turn it on after config.g is run. Control it with a spare pin and an SSD.

Updates: Its been a minute since I figured this out and I am just now returning to troubleshoot more.

I am able to effectively control the laser via M42 commands on P3.

When it powers up, the laser is defaulted in an on state. I can send M43 P3 S0 F250 and bring it to a safe/off state.

Laser power/12V Power is being pulled from the fan jumper header (duet 2 wifi).

When I run a "print", I get a somewhat effective print now, however, the laser is not fully going to an off state between G1/G0 commands. See picture for example. The deep burn is time between power on and getting the M42 command sent.

I feel I can overcome some of the issues with effective config gcode and some tweaking of my run gcode. But I'd like to figure out the why/how to keep the laser from coming on during travels.

Note: still using Firmware version 2.04

Took some time over the weekend to troubleshoot.

I dropped back to 2.04, this has helped a ton in keeping things simple and aiding troubleshooting.
(Sidebar, did the complexities in pin naming come about with the Duet 3 out of necessity?)

I snagged a cheap oscilloscope to run some troubleshooting. After some baseline familiarization and effort with the oscilloscope on a PWM fan pin I finally figured out what I needed for PWM measurement.

I turned the Heater 3 pin into an I/O pin and dabbled with the settings. I'm not sure if it was human error but I had some toruble getting a good PWM waveform using S1-255, but after shifting to S0.0-1.0 I started yielding exact outputs as were set. So the TLDR is Heater3 is working properly for PWM.

So my next venture is to determine if Heater 3 PWM outputs properly in laser mode. (I assume it will)

Next step is to test the other side of the 74HCT02D with I/O pin setup.

@o_lampe Thanks, I'll look into it!

And the firmware rollback was definitely something I was considering doing, but didn't want to jump to initially. But I think its and excellent option to try. (Typical troubleshooting is to go "did you use the latest stable release?" so a bit of reverse logic to go that far back, but it is what I know and have had work in the past)

@dc42 @dc42 when I say expansion board I mean the 74HCT02D breakout board that mounts in the expansion slot. Not an actual Duet expansion product.

This is the board I am using https://forum.duet3d.com/topic/8705/laser-pwm-module-with-circuit-protection/4?_=1709574473662

A lot has changed, and utilizing the “Configuring RepRapFirmware for a laser engraver/cutter” isn’t helpful in the process beyond updating the config to current firmware.

The lack of M3/M5 commands has also been troublesome while troubleshooting, but I don’t think that is my issue. (I saw the recommend work around with U axis and potential future add for focusing)

What can be done to confirm that PWM is outputting effectively on the Heater 3 pin? (From what I understand simply measuring voltage isn’t enough)

Hi all,

Its been about 6 years since I last touched the laser function of Duet.

I have an expansion board from the early tutorial and Duet 2 Wifi made circa 2018.

I am having trouble since coming back with issues of the laser being on and firing at a high enough level where it is not safe on boot (enough to burn wood).
(Similar symptoms to this post https://forum.duet3d.com/topic/19565/laser-not-turning-off)

I have upgraded 2 different boards to 3.4 and 3.5 and still seem to have the issue. I have also used two separate PWM expansion boards (74HCT02D).

As the firmware has progressed there is A LOT of jumbled mess and versioning (improvements?) to sift through for configs. I am not a fan. Before it was straight forward. I'm sure most changes have happened for logical/safety reasons but definitely not making the journey easy.

So the question: In laser mode: M452 C"exp.8" R255 S0 F200; (Also tried with exp.heater3 pin defined)
(Feeding the 12v from fan: always on, with jumper to 12v fans)
Should the PWM voltage from pin 8, always be ~5v (reading in the high 4s normally)

This occurs with laser enabled, or disabled (code commented out), S255 or S0, and on both boards.

Any insights as to what I am not doing correctly here?

Ended up fixing the mosfet to a P. Board ordered, assembled, and printed like a champ. (if anyone U.S. based is also pursuing a laser project PM me, I have extra boards now due to min order qtys. with and without mosfet design (PCB only))

Awesome, thanks, I was just noticing that myself that the diode direction was wrong and going back to figure out the "why" N vs P channel is exactly the why.

I have ordered a PCB for the Laser PWM Module created by @keyz182.
Developed Here: https://forum.duet3d.com/topic/4632/laser-wiring
Mentioned Here: https://forum.duet3d.com/topic/6136/laser-pwm-module-v1
Write-Up Here: https://duet3d.dozuki.com/Wiki/Laser_PWM_control

After ordering one, I got to thinking about an addition I would like to make. Due to a polarity error I had when my laser was wired up to an Sbase, I had to go back and replace a mosfet on the laser controller that fried. IN order to prevent this and help others out I was hoping some polarity/circuit protection would be useful.

My background is in Mech Engr, so circuits always take me some work to get through. I was looking at using a mosfet to add that protection.
Reference: "How to Protect Circuits from Reversed Polarity" https://www.youtube.com/watch?v=IrB-FPcv1Dc

This was what I came up with:

Can anyone provide input on the addition of the mosfet and whether or not this is a good idea or not?
Additionally, a sanity check on the selected mosfet would also be appreciated. Ive gimped my way through redesign the PCB as well and can post those changes from EasyEDA if requested.