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Thread: ILDA specs

  1. #1
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    Default ILDA specs

    If I remember right the brightness control is 0-5 volts, I have a Laserdoc as the DAC but I am not seeing voltages that hig, I am thinking it just may be the drop across my cable but I was also wondering is the signals from the DAC need a buffer, can you directly connect the lines to the driver boards (i.e. for the intensity ) or should I build a buffer into the projector for that? I know there is very little current but I don't want to damage my DAC as well, line drivers and buffers are easy to come by and was wondering if I should put a buffer on the receiving end? I have the brightness control on the software at full output but still only seeing about 2 volts at the driver, I don't want to load down the DAC , but it could just be the voltage drop across the cable, I made the ILDA cable my self from a printer cable just with the compatible DB25 connectors on the other end and it's all working but just not seeing the full voltage on the other end

    The drivers I am using are the Simple Drive 2500 units modified per BBE's recommendations to drive lower current single mode laser diodes, I like that model driver as in the future I may convert them back to there original current ratings

    Thanks
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

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    Have you tested at the DAC with no cable to see if that is the issue?
    I have never had the need to do anything special. It could be a bad cable or bad DAC.

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    If you're only seeing 2V at the driver then something is wrong, but it's hard to say what without more info. The cable should definitely not cause any appreciable drop at any reasonable length. It's possible that the DAC actually has symmetrical differential outputs, and is putting out +2.5V/-2.5V on the modulation +/- lines, but I would be very surprised if that were the case.

    Testing the DAC and cable independently would be a good place to start.

    Can you give us a look at how your projector is wired up?

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    it's very possible his meter is too slow and he's trying to measure a modulated output.

    Quote Originally Posted by aberry View Post
    If you're only seeing 2V at the driver then something is wrong, but it's hard to say what without more info. The cable should definitely not cause any appreciable drop at any reasonable length. It's possible that the DAC actually has symmetrical differential outputs, and is putting out +2.5V/-2.5V on the modulation +/- lines, but I would be very surprised if that were the case.

    Testing the DAC and cable independently would be a good place to start.

    Can you give us a look at how your projector is wired up?
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

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    Agree with Chris. You need an oscilloscope to properly check modulation signal intensity.

    Even when displaying a solid circle that is completely white, the controller will still be blanking the lasers periodically. A multi-meter will not interpret a modulated (blanked) color signal properly. The only way to be sure is to check it on an oscilloscope.

    I'm not saying that it's isn't a problem with the controller, or the cable, or whatever. It very well could be that the voltage is in fact too low. But the readings on the multi-meter are basically useless; until you check it on a 'scope you can't be certain what the voltage level is.

    Note also that a "buffer board" won't solve the problem if you really are losing voltage down a lengthy cable. Buffers by definition take whatever they see on the input and re-create that signal on the output. Unless you also include a GAIN ADJUSTMENT stage, a buffer by itself won't amplify the signal back to the 5 volt level.

    Adam

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    Good advice. Lacking an oscilloscope, he could just provide +5v directly to the modulation inputs of each laser to see what that does powerwise. If that does the trick, then start working backwards to isolate the problem to a controller board, cable, DAC, or software.

    David
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    It totally slipped my mind that the modulated signal would be out of range for a DMM, when I set the gain on the driver it was with a DC signal, I will check it with my scope when I get the chance.
    Thanks
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

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    Quote Originally Posted by buffo View Post
    Agree with Chris. You need an oscilloscope to properly check modulation signal intensity.

    Even when displaying a solid circle that is completely white, the controller will still be blanking the lasers periodically. A multi-meter will not interpret a modulated (blanked) color signal properly. The only way to be sure is to check it on an oscilloscope.

    I'm not saying that it's isn't a problem with the controller, or the cable, or whatever. It very well could be that the voltage is in fact too low. But the readings on the multi-meter are basically useless; until you check it on a 'scope you can't be certain what the voltage level is.

    Note also that a "buffer board" won't solve the problem if you really are losing voltage down a lengthy cable. Buffers by definition take whatever they see on the input and re-create that signal on the output. Unless you also include a GAIN ADJUSTMENT stage, a buffer by itself won't amplify the signal back to the 5 volt level.

    Adam
    Actually an actual buffer amp is a high impedience device that will pretty much ignore the trivial amount of resistance from a long cable...
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

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    Hehe, finally someone complaining about the color signals not reaching a full 5 volts, and not accusing Pangolin of being too dumb to make hardware capable of doing that, and accusing us of completely overlooking the fact that USB is rarely a full 5 volts...

    I used to love those conversations (not!). Of all of the things we got right, the single thing we overlooked is that you need 5 volts on the color signals and this would be IMPOSSIBLE with a USB device. (They'd overlook the fact that the X and Y signals did swing the full 5 volts...)

    Anyway, getting back on topic, yes, using a volt meter you will NEVER see the color signals reach a full 5 volts UNLESS the driving software asserts the color signals to hold the maximum voltage. In all of our software we prevent permanently holding color signals at 5 volts for safety reasons. (And we would not use a sound board to control a laser, again for safety purposes, but that's a different story... What people do in the privacy of their own home is their business )

    Bill

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    Quote Originally Posted by Pangolin View Post
    In all of our software we prevent permanently holding color signals at 5 volts for safety reasons.

    Bill
    Thanks Bill, this bit of insight is very interesting. Using Quick Show or LSX with my Chinese Magnum Lighting 1W projector color on/off transitions are quite smooth. Using a 74HCT TTL buffer to drive the colors through TL084 gain-control opamps I noticed on/off transitions are not as smooth as QS or LSX over a range of output voltage maximums (4-5v). Colors initially come on bright then dim a little almost like they are becoming over-damped in the projector electronics then settle down very quickly. This only occurs at the initial frame of an image while repeating frames are not.

    Being and old laser fart "new" to ILDA based projectors and standards I'm interested in insights to this behavior.

    In terms of DVM vs scope we used to say "you got to see it to believe it".
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