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8955Re: [diy_3d_printing_and_fabrication] RE: RE: RE: RE: Highest DIY XY resolution ?

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  • Jon Elson
    Oct 14, 2013
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      Reinis Veips wrote:
      > Do you mean this one: http://wot.lv/scanning-laser-projector.html ?
      >
      > I did it, but I didn't like the results. It was done on ARM MCU development
      > board from TI- Stellaris (now Tiva) Launchpad.
      >
      > Main problem was- how to detect start of the line condition reliably. I tried to use
      > ordinary LED (with peak emission wavelength a bit above what I wanted to
      > detect), which generates tiny current when hit by laser. Projected pattern
      > shifted back and forth- it never stayed at exactly the same place.
      >
      The original laser mechanism has a photodiode in the path to sense the
      start of the
      sweep. My guess is that thwe circuit you were using was photoelectric,
      ie. no
      reverse bias on the photodiode. If you run it in photoconductive mode with
      reverse bias, it greatly reduces the capacitance of the diode, allowing
      you to
      get a much faster response to the light pulse. It is also possible you need
      a different diode to be sensitive to the UV laser. LEDs can't take a lot
      of reverse bias (5 V might be the max) so a diode made specifically for
      light sensing applications might be better.


      Jon
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