Pulsewidth control via firmware?

edited September 2017 in Questions & Answers
So i'm building a powder based printer and got a short question about the operating the laser.
I planned on using repetier-firmware in laser mode using this https://lasertack.com/2a-smd-laserdiodentreiber-2 driver and controlling the laser output via plusefrequency and pulsewidth.
As recommended i wanted to use the Extruderstep signal for frequency but is there a way to control the pulsewidth of the E-steps via firmware or do i need an external circuit for that?


  • The default implementation included does only enable/disable laser. The firmware event system is prepared to also set an intensity, but requires an own solution, especially a hardware controlled PWM pin or external hardware with PWM control. In laser mode the extruder pin gets no signals at all. You would configure slicer to always use same fixed width and only enable laser by increasing e value like slicers would create it.
  • Ah alright then i misunderstood how the laser mode works...
    But couldnt i then just go ahead and use the normal Fdm-mode with a dummy Hotend and use the Extruder-Steps as modulation for the laser?
    Would probably still need an aditional arduino which gets the Step/mm pulse signal and resets it to a given pulsewidth if that isnt changable in the firmware...

    Thanks a lot for the reply!
  • edited September 2017
    this driver works only with pulse width modulation or analog modulation.
    operating frequency is fixed and around 1 kHz is ok.

    as i work with this laser driver for half a year now i can tell you it works best with analog modulation.

    to get good results with this driver you have to use external pwm driver or external dac.
    code / schematic you can find here:

    https://github.com/repetier/Repetier-Firmware/tree/development/src/SampleEventSystems/Laser PWM and DAC

    if you can explain your exact needs a little more detailed may be i can help you .

  • Hey RAyWB,
    thanks a lot for offering ur help! Im pretty new to the laser topic so excuse me if i mistake some things...
    Im builing a SLS-Printer using a 2W 445nm Diode-Laser from Lasertack with the linked driver and a radds to control the whole printer.
    My first thoughts were that its probably the best way to use the extruder steps for modulation since they are linked to the x-y-movements of the laser.
    But since u are probably more experienced then me i would really appreciate some help. ;)
    If u need more details on anything tell me.
  • edited September 2017
    ok, so you wrote it will be powder based , not the one with liquid ?
    what´s your hardware? Mega/Ramps?
    are you shure the 445nm is ok for melting the powder?

    think the modulation is the minor problem you´ll have.
    as far as i can see you just need adjustable power at the moment to get started.
    did you already test the diode ? what´s the focal length?
    how do you prevent lens from smoke ? smoke will cause a layer of "dirt" on lens very very fast
    causing power loss and may end up in killing laser by self reflection.
    (killed myself a 5W laser diode by dust <1second).

    you´ll run in a bunch of problems, starting with rectangle shape of conical (not parallel) laser beam
    over pretty short focal length.

    that´s just a few issues that need to be solved. as far as i know the professional sls laser systems
    are working with mirror systems driven by galvanometers and using lasers based on diode pumped tubes
    or Fiber coupled lasers.

    for the optical issues the guys form lasertack can help you (beam correcting to nearly square)
    you just have to call them , from my experience they are friendly and have a lot of knowledge.

    what´s your native language?
  • Yes its a powder based system.
    Hardware is Due/Radds.
    Should be working im planning to only use dark powders or mix white powders with industrial carbon.
    Im going to preheat the powder therefore the laserpower should be high enaugh.

    Adjustable power is exactly what im looking for. I thought the most accurate way is to do it is via pulsewidth.
    Like longer pulses equals more power - shorter pulses less power, but again that could just be me misunderstanding it...
    Didnt test the diode yet, since its my first laser based project and im afraid to straight up kill it :D
    The focal length planned in my build is between 40-50mm. Should be close enaugh to get a more or less good spot.
    The laser works in an enclosed chamber to protect it from fumes and especially the heat.
    The space between the powderbed and the laser is shielded by a quartzglas plate which lets 95% of the Laser pass.
    I hope there wont be too much smoke anyway since i just want the powder to melt and not burn/vaporize.

    Yeah their new spotcreator setup looks nice but was a little too expensive for me just to test if i can get a system like this to work. If ill run into problems with divergence of the beam ill hit them up for sure.

    My native language is german.
    If u send me ur Email i can hit u up with some pictures of the build. ;)

    Greetings and thanks a lot for ur time.

  • ok, schicke Dir heute Abend meine mail-add per pm , und auf deutsch wirds sicher leichter :-)
  • Alles klar, klingt gut ;)
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