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Thread: Controlling 2 lasers with one DAC?

  1. #1
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    Default Controlling 2 lasers with one DAC?

    <newb>

    I've reached the point where I just about understand the workings of my single beam (green) scanner. So I was thinking about adding a second beam (red).

    <theory>
    So to do this I need a dichro mirror to reflect green and pass red (or vice versa). Then by careful blanking control I get get Green, Red and Yellow, correct?
    </theory>

    I have a MediaLas USB DAC with a standard ILDA connector. Now this only provides blanking for one laser, but there are a bunch of other outputs (R,G,B +/- etc...).

    I also have Mamba Black control software - is there anyway to wire up the blanking of the additional red laser to this output so that the software can create RGY images?

    Steve

    </newb>

  2. #2
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    Default

    Yea, use a dichro to combine the beams and then blank each laser seperately. You would use the RBG connections instead of the blanking connection in this case.

  3. #3
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    Default

    OK that makes sense, what if one laser has analog, but the other only has TTL - would this be a problem?

    I would assume that is the blanking goes over 'X' volts then the TTL trigger would sense a high and switch on?

  4. #4
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    Default

    If you have analog out to a TTL in then you will have unpredictable results when you are at the midrange voltages. So, if you have a TTL laser attached to a DAC with analog outputs you should either use full color or no color. It won't hurt anything electronically but who knows what you will get when you send 2.5V to a TTL input.

  5. #5
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    Cool

    Yeah, but the valve of that "X" voltage varies. Most TTL blanking circuits switch on well before 5 volts. (Some will turn on at as low as 1.5 volts.) Still, it's not really a problem, since most frames have fairly bright colors. But if you send a frame that has very dim colors (below the turn-on threshold for your TTL laser) then those colors will not show up.

    You can mix analog and TTL lasers, but you won't get as many colors. (Obviously) Still, having one analog laser and one TTL laser is better than just two TTL lasers.

    BTW, traditionally you use a reflect red, transmit green dichro to mix the two, but it will work the other way if you find the right dichro. (With most dichros you loose more power from the transmitted beam than the reflected beam.)

    TTL will give you just 3 colors - green, red, and yellow. Analog on at least one of the two lasers will give you some control over the yellow shading. Analog on both lasers will give you everything from red through orange and yellow to green.

    With all analog blanking you will also be able to vary the intensity of a given color. (Say you get the perfect orange at a 5:1 ratio of red to green... You can have that ratio with the resulting beam at 50 mw or at 200 mw or anything inbetween. Same color, different brightness...)

    You don't use the blanking output (normally labeled intensity, BTW) on an RGB projector. You use the individual color signals for red, green, and blue. The intensity signal is for monochrome projectors.

    Adam
    Last edited by buffo; 09-14-2007 at 09:52.

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