SPINDLE_LASER_FREQUENCY fix

[Ashammaru]

Description

Fixes SPINDLE_LASER_FREQUENCY setting being overridden by analogWrite, which forces the PWM frequency to a default value at 1khz.

MARLIN_DEV_MODE frequency command still doesn't work though, but it may be user error on my part.

Confirmed to work with oscilloscope, but not tested during actual cutting. Board: SKR 1.1 Pro

Benefits

Fixes SPINDLE_LASER_FREQUENCY adv config setting not actually changing the PWM frequency. This may cause issues when controllers often require frequencies far beyond the default 1 kHz.

Configurations

https://github.com/MarlinFirmware/Marlin/blob/bugfix-2.0.x/Marlin/Configuration_adv.h

[shitcreek]

Reviewed and tested with oscilloscope.

[Ashammaru]

This is a bit out of scope for this request but I have also been looking to add new M-codes to change the PWM frequency, one to change it and one to reset to default. If you switch the signals so the laser psu power is always 100% and use pwm to turn it on/off you can make a laser pulse at the frequency set in marlin and use the duty cycle to control pulse energy, while keeping the line energy the same, which would be great for different materials and especially for low-power engraving with more powerful lasers. It could also add some new raster methods by matching certain speeds with a pulse frequency, and maybe even match it with accelerations when cornering which should improve the cut quality.

I have got it working with my original patch, as it needs some kind of persistance, but it should be broken now and my coding skills are not the best. Would it be better to submit as a feature or pull request? I can probably implement it properly with config settings etc but I have no idea how many bugs I would introduce 😬

Thank you.

[thinkyhead]

If you switch the signals so the laser psu power is always 100% and use pwm to turn it on/off you can make a laser pulse at the frequency set in marlin and use the duty cycle to control pulse energy

Which laser / cutter devices are specified to work in this manner? It would be helpful to gather together the spec sheets for some common laser and cutter devices and their power circuits so that we can add to our Laser / Cutter page on the website a helpful table of specific Laser / Cutter brands and models and the most appropriate settings for each one.

[Ashammaru]

Which laser / cutter devices are specified to work in this manner? It would be helpful to gather together the spec sheets for some common laser and cutter devices and their power circuits so that we can add to our Laser / Cutter page on the website a helpful table of specific Laser / Cutter brands and models and the most appropriate settings for each one.

Not any one in particular, but I know the Lasersaur project did this really well with their control boards and cheap chinese C02 lasers. Here is an old thread on it https://groups.google.com/g/lasersaur/c/bJ2l5-dlsJo/m/8YCq_tLZ7usJ AFAIK most cheap chinese PSU's are very similar, and maybe even made in the same factory with just different brands slapped on.

Any laser system with native pulse control probably has its own firmware, control software and use a separate signal. Nothing for hobbyists or Marlin users I think, too expensive and integrated. LED lasers probably don't need it as they are low power enough as it is.

Our 100W Lasersaur works really well, but the control program hasn't aged well and the firmware isn't supported anywhere so we are looking at replacing it with a Marlin board and laserweb/light burn instead. Our first tests using the manufacturer specified control signals was really bad and just cut/drilled holes in everything but that was before I found the PWM frequency bug so it may be better now, but optimally we would want to automatically lower the pulse rate for low S values and/or let users set their own pulse rate.

We will run tests for it in the coming weeks, I can document everything and compile it in a pull/feature request.

Edit: I will have a look at the wikipedia page when I have time, its a bit outdated now. I could add some wiring circuits too but they are usually in the PSU manual if it has any.