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Thread: Questions about TTL color control...

  1. #1
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    Default Questions about TTL color control...

    MechEng3 and I have been discussing the pro's and cons of various laser projectors, and we've come upon something that doesn't exactly make sense to either one of us. So this is a call to Specwhore, Yaddatrance, Marconi, and anyone else that has experience with full color control... (Note that this whole excercise is more to understand the theory of operation than to get it hooked up right - MechEng3's projector already works just fine!)

    MechEng3 is running the EasyLase USB controller and Laser Design Studio software from JMLasers.com. (And let me say right now that I'm insanely envious of his compact, *portable* whitelight projector! I can't wait to see it at SELEM this summer!) Anyway, as best as we can tell, the color output on the EasyLase controller is TTL, which I assume to mean +5 volts for blanking and 0 volts for on. All three of MechEng3's lasers are solid state, and they all support TTL blanking.

    Now, the Alphalite XC Pro controller (and software) from LaserIllusions.com also supports TTL color control. But while I haven't yet received my Alphalite, I've spoken with several other Alphalite owners and they all say the same thing - namely that you only get 8 colors with the Alphalite: White, Black, Red, Green, Blue, Yellow, Pink, and Blue-green.

    However, MechEng3 is able to get a full range of colors, from oranges and various shades of yellow, to yellow-greens, violet, purple, light blue, etc...

    I'm wondering how this is possible... Does the Easylase unit use some form of pulse-width modulation to emulate analog color control? (IE: vary the duty cycle at extremely high frequency to simulate varying intensity?) Because if it is doing this, it's got to be running at least an order of magnitude faster than the galvos or otherwise you'd end up with dashed lines instead of smooth traces, right? And just what is the frequency limit for TTL modulation on a DPSS laser anyway?

    I always thought that true RGB color control was accomplished with an *analog* color output signal from the controller that either went to the *analog* intensity control of each laser, or to the input of an AOM/PCAOM to control intensity.

    So, can anyone shed some light on this issue for us?

    Adam

  2. #2
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    Easylase has 8 bit resolution on every color (RGB). It outputs an analog voltage to the lasers. Only blanking/intensity is a digital signal or analog as I understand it.
    You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads!

  3. #3
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    Quote Originally Posted by Groover
    Easylase has 8 bit resolution on every color (RGB). It outputs an analog voltage to the lasers.
    Hmmm... Ok, so that means that you have to have an analog intensity control on your driver circuit for your laser, right? IE: the circuit takes some varying DC voltage (say, zero to 5 volts) and converts it to a varying drive current?

    So then if you don't have a laser that supports analog intensity control, you can't get full color control...

    Adam

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    I would think so. But lets hear from the pro's here first.
    You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads!

  5. #5
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    Heres a video of mecheng's setup.

    http://photonlexicon.com/hostedcontent/pl_vid2.wmv

    The color shifts are pretty rough for analog, though that could be just the ild file.

    Assuming everything is ttl then his rig is really utilizing it.

    Say it switches from 0-5v and so on over 3 points for red and only does one point of green. that would give a rough orange, add another green point and you have yellow. At that point it becomes a persistive vision trick.

    Im thinking theres an analog laser in the woodshed so to speak: maybe when they sent back his green from China it had analog...

    Ive asked Mech to connect some AA batteries between the blanking leads of the green and blue laser to really determine if theres analog present. if it dims with 1 2 or 3 batteries then its analog.

  6. #6
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    Ok... That makes more sense to me. Using pulses of varying duration to approximate intensity and relying on persistence of vision to average them out.

    I watched the video, and the colors do seem to blend. Still, it could just be that the easylase unit is really good at TTL color mixing.

    I'm also curious to discover what happens with the 1.5 volts, 3 volts, and 4.5 volts applied to the blanking input on the lasers. My guess is that somewhere around 4.5 volts the laser will simply blank. (Come to think of it, I can try this myself on my Lasever unit! Just gotta find that stupid blanking cable...)

    Adam

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    what a great thread

    This is something i has wondering about for a looong loong time !

    I really did start wonder about this when I was planning to add RED and BLUE as well to the green !!

    If there is ONE blanking output (and i use that to the green laser)
    what blanking is the RED laser support to use then ??


    and if i connect the red on the RED output, and blue on blue, and green on the green output ..
    When there is NO signal red\blue\green it`s "blanked" ok?
    So why is there a blanking output then ?


    there is alot i dont understand here

  8. #8
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    http://photonlexicon.com/gallery/mecheng?page=2

    this is the best I could find in the test pic files that was close to what hopefully will answer the task at hand.
    You are the only one that can make your dreams come true....and the only one that can stop them...A.M. Dietrich

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    OK after some investigation here is what is found. We have measured the output signals from the easylase unit and found the signals to be 0 - 5 volts maximum differential. However it is analogue. This is ,I am told, to be very close to TTL as far as the laser is concerned. This is why this unit is able to blend colors and be able to vary the intensity. As a symmetrical output from the USB to the ILDA 25 pin connector, TTL signals by default are selected from the software output. Then it knows and is only able to output the upper half ,if you will, of the analogue signal. Please correct me if I am wrong. I have contacted Joachim and he is confirming our findings. He also stated that there is no risk of damage to the unit or the lasers. There is a TTL output on the board but it must have a 74hct241 opto coupler on each output [R_G_B} to protect the circuit from incomming voltage. There is a jumper pin on the board itself . An option for analogue or TTL output. TTL is the default setting IF all color values and intensity are set to 0. If there is no output or a laser on all the time, change the jumper setting and recheck pallet color setting. All colors set to 1 or full color , the analogue signal output is present. I am pleased to find this as it may help with the questions I could not answer. Now I am still investigating the other software available. I would like to see a page with all the different functions of this software and other systems to offer a perspective for someone looking to get in the hobby or for someone that may want to add to their arsenal.
    You are the only one that can make your dreams come true....and the only one that can stop them...A.M. Dietrich

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