Problem getting a laser to work

dc42

If you have laser mode selected using M452 then you should not be trying to extrude. Laser mode uses M3 to set the laser power.

Is this an existing system that was using M571 to control a laser and you just want to upgrade the firmware, or is this the first time you have connected a laser to a Duet?

appjaws

Thank you so much, I now understand and can report that using M3 to control the laser works.
I knew it was my lack of understanding.

This is a new installation of a laser onto my ormerod using Duet 6

appjaws

I have something very strange.
M3 S255 turns the laser OFF as does M3 S0
It appears that the maximum power is around M3 S127

keyz182

@appjaws said in Problem getting a laser to work:

I have something very strange.
M3 S255 turns the laser OFF as does M3 S0
It appears that the maximum power is around M3 S127

Try lowering or increasing the PWM frequency with the M452 F parameter. Some of the laser module controllers are a bit picky. You can also use the R parameter of M452 to set the PWM level that corresponds to max, so in your case, R127.

appjaws

I tried changing the frequency but could not see any improvement.
I am currently using M3 S107 as my maximum power.
It works but I would prefer to have 255 levels of power, especially engraving photos.
Any other ideas as to how I can use the full range?

resam

@appjaws which laser and laser control board did you buy?
Most of them use a "simple" PWM signal between 0-5V to control the laser intensity.

I doubt that your laser really has a 50%-ish PWM signal as "full power" signal...

appjaws

I've just measured the voltage on the Fan0 pin and it is fluctuating between 5.5V - 10.7V.
Do you think I am over driving the PWM input?
The problem I had no information supplied with the 2000mw laser and control board that I bought.
I have tried to find out the correct voltage but was unsuccessful.

This is a picture of the laser I bought

keyz182

@appjaws said in Problem getting a laser to work:

I've just measured the voltage on the Fan0 pin and it is fluctuating between 5.5V - 10.7V.
Do you think I am over driving the PWM input?
The problem I had no information supplied with the 2000mw laser and control board that I bought.
I have tried to find out the correct voltage but was unsuccessful.

The ones I've seen have all been 5v PWM controlled, so maybe you're over-driving? Do you have a link to where you bought it? And/Or some high res images of the top+bottom of the PCB?

appjaws

I bought it on ebay and the supplier has no information.
I could take some photos of the board but I will need to dismantle my setup first.
I wonder what size of resistor I could connect in series to reduce the actual voltage reaching the control board

resam

Me, and others here on the forum use the HEATER_3 pin with a few extra components, instead of the fan output. Somebody even made a custom PCB for it.

https://duet3d.dozuki.com/Wiki/Laser_PWM_control

appjaws

I did start with that plan but could not get my lashup to work. I now have a better understanding so perhaps I'll try heater 3 again.
Thanks for your help.

appjaws

I still haven't got the heater 3 solution as explained in the article "Controlling a PWM Laser with the Duet Board" The diagram indicates that the expansion header pin 8 is heater 3 but I have a constant 3.29 volts between that and pin 2 which is grd.
So I am wondering if the old version 6 boards, which I am using, have the same pin assignments as the version 2 boards.

So I have reverted to using the fan connector with the output reversed and a pull-up 1K resistor connected to +5V.
This is the results of checking the voltage at different S values.
Svalue Voltage Laser
0 4.4
10 2.58
11 2.47
13 2.33 ON
15 2.27
20 2.19
40 2.05
60 1.97
80 1.88
100 1.77
120 1.64
140 1.51
160 1.39
180 1.27
200 1.14
220 1.08
240 0.87
250 0.78
252 0.77
254 0.75
255 0.74 OFF

The increasing S values at the top end result in the power of the laser reducing.
Clearly I have something wrong but I am at a loss as to what to do next.