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Thread: projector building: setting max driver current question

  1. #21

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    Quote Originally Posted by kecked View Post
    You want brighter get higher power projector.
    bu.. but I'm the one building it. What's the point of cramming in more diodes if I can just make the ones I have already installed draw more power? Or why should I have them underperforming and instead adding more diodes? That seems illogical. These are the questions.

    At a certain point low in power your eyes saturate. All get after that is a lose of background contrast as the reflected light lights up the room. I e en tried projecting on black cardboard to fight this. Dimmer image but better contrast.
    For beam shows dude.

  2. #22
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    Why can't Pangolin and other laser programs have a command to turn on the color DAC's full power +5V for testing? My projector control console has three DMX channels that can send +5 to RGB for manual full power color control. A fourth DMX channel switches between manual color control and ILDA color control.

  3. #23

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    If lasers were a bigger pie in my business I'd just buy the testing tool Stanwax sells, or build my own. After all you just need a AC to 5V DC converter and few trimpots + two ilda connectors in some box to make this work, but I just don't bother right now as 3d mapping and dmx is mainly what I do.

  4. #24
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    Quote Originally Posted by Finale View Post
    Thanks Adam, but I'm measuring the current and with an LPM, no voltage.
    This is even worse. The power meter will respond slower than the voltmeter will.

    Simpledrives have pins which allow to measure the current with a voltmeter.
    Except that to measure instantaneous current accurately when you are sending a modulated signal to the driver, you must use an oscilloscope, not a voltmeter, to perform the measurement.

    You can only use a voltmeter when you are sending a constant DC signal to the modulation input on the driver, such as when you first set up the driver and are adjusting max current with a battery (or DC power supply) connected to the modulation input.

    When you have the driver hooked to a laser show controller you are never going to be sending a DC modulation signal. There will *always* be some modulation present, even when displaying a static dot at full intensity. This is by design and is a safety feature that nearly all controllers incorporate.

    With lower power simpledrives it's 100mV = 1A and with the 5A version it's 50mV = 1A.
    I know. All drivers have a current-sensing resistor on the output. It's an integral part of every laser diode driver.

    Using ohms law its easy to see that the low power simpledrive uses a .1 ohm resistor for current sensing, while the high power version uses a .05 ohm resistor. So when you measure the voltage across that resistor, you can calculate the current flowing through it.

    But your voltmeter doesn't know what to do with a modulating signal, so it will AVERAGE the voltage over time. This gives you an artificially low reading. This is why you must use an oscilloscope, so you can get an instantaneous reading of the voltage across that resistor.

    I don't know if the modulation would affect this reading.
    I do know (as do many others who have posted), and yes, it absolutely will affect the reading. Use an oscilloscope. This has been covered in previous threads ad nauseam.

    Quote Originally Posted by Photonbeam
    Why can't Pangolin and other laser programs have a command to turn on the color DAC's full power +5V for testing?
    There are solid safety reasons behind the decision to crowbar the modulation lines during a frame buffer update. To bypass this opens up a huge can of worms. And the only benefit is for the edge-case of someone building their own projector who wants to set the max diode current on the driver using a controller and not some other DC source.?.

    That's silly. If you are building a projector, you already have access to all the internals. Connect a power supply directly to the modulation lead and set the current that way. Or use a battery. There's no reason to connect a controller to a projector until everything is fully assembled and tested anyway.

    My projector control console has three DMX channels that can send +5 to RGB for manual full power color control. A fourth DMX channel switches between manual color control and ILDA color control.
    How often do you need full 5 volts (unmodulated) on the projector, and why do you need it? What would you be doing from the control console (presumably during show setup?) that would require unmodulated color? You certainly don't have the hood open to tweak driver current settings before a show, do you?

    If it's just for convenience, you could do the exact same thing using the control software. You can send "all white" to the projector at any time from within Showtime or Lasershow Designer (or Beyond, for that matter). In fact, if you still wanted to use DMX, you could still do it - just bring the DMX into Beyond and use it to trigger an all white color effect.

    But of course, using the controller there will be breaks in the modulation signal each time the frame buffer updates. This is by design, and it is part of the safety built-in to the controller. This has no effect for 99.9% of what anyone would be doing with a projector.

    However, your solution of bypassing the controller's color control adds a huge safety risk for no real benefit. (With your DMX color bypass, the software could tell the projector to stop outputting light and stop scanning, but instead it would only stop scanning, leaving you with a single static beam at maximum brightness. Not cool...)

    Adam

  5. #25

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    I did not know how the current from the driver was being read via a voltmeter and whether that current would be affected by the modulation as well so I asked. Sorry if I sounded like I was arguing with you and sorry if you had said this already and I had missed it, I had no intention to argue, only learn.

  6. #26
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    Quote Originally Posted by buffo View Post
    ....How often do you need full 5 volts (unmodulated) on the projector, and why do you need it? What would you be doing from the control console (presumably during show setup?) that would require unmodulated color? You certainly don't have the hood open to tweak driver current settings before a show, do you?

    If it's just for convenience, you could do the exact same thing using the control software. You can send "all white" to the projector at any time from within Showtime or Lasershow Designer (or Beyond, for that matter). In fact, if you still wanted to use DMX, you could still do it - just bring the DMX into Beyond and use it to trigger an all white color effect.

    But of course, using the controller there will be breaks in the modulation signal each time the frame buffer updates. This is by design, and it is part of the safety built-in to the controller. This has no effect for 99.9% of what anyone would be doing with a projector.

    However, your solution of bypassing the controller's color control adds a huge safety risk for no real benefit. (With your DMX color bypass, the software could tell the projector to stop outputting light and stop scanning, but instead it would only stop scanning, leaving you with a single static beam at maximum brightness. Not cool...)

    Adam
    Adam, my "projector" is an old school 10 position beam table with scanners, machida gratings, lumia, presets for mirror bounces, fiber launches, etc. When running a color beam or graphics show with the scanners I use the ILDA color signal. For other effects like the machida grating or lumia, it's nice to be able to use full power of any color. It's probably not something you would need otherwise.

  7. #27
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    Quote Originally Posted by Finale View Post
    Sorry if I sounded like I was arguing with you
    Fair enough. And I'm sorry if I got a little testy.

    If you connect an oscilloscope to the test port on the driver, you should see a square wave on the screen. By counting the graduations, you can tell how high the peak of the waveform is. Then look at the scale setting on the 'scope to see how many volts per line, and you can figure out the modulation voltage.

    And yeah, if after doing all that, you see that you have at least 4.75 volts, then you are OK. But if you see something like 4.1 volts, then you do have a problem...

    Adam

    PS: An oscilloscope is a very handy tool to have. If you don't have one, they can be had on E-bay for around $100 or so. Might want to pick one up...

  8. #28

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    I see. Yeah, those old analog oscillicopes are cheap, someone was offering me one for $80. I'm split between getting one of those or the Hantek PC oscilloscopes. Hantek requires a PC but on the other hand using a laptop's screen and a friendly UI seems a better idea. It only goes 20mHz but for laser work should be more than enough.

  9. #29
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    I use a Stanwax ILDA Gem for my 5V but really any constant 5V regulated source will do. You may well have at least one already in your projector.
    I've entirely stopped setting my projector powers by current as its a total faff, and when you're doing pair of projectors, you don't want them on the same current, but one doing 500mW and the other doing 600mW due to differences in diode efficiencies.
    I now set all of mine by target power and constant 5V.
    .
    So any 638 build will be dialled in for 700mW per diode.
    Any 700mW 520 for 800mW
    Any 1W 520 for 1.2W
    etc
    .
    We know well enough these days what is a typical power to be expected from a given diode and how hard extra we can reasonably push them. Also helped by the protection being built into the blue and greens too.
    If I pop one prematurely or in setup its because it was a bad diode to start with, and one I probably wouldn't want in a show projector anyway.
    I squeeze just a bit extra out of the diodes to make it worthwhile, whilst not trying to go to extremes. If I want more than one diode can give, it becomes a multi diode setup.
    .
    If you want to test power using a DAC then use the LaserMedia test pattern (square with 45 degree rotated square inside it and big cross through the lot) as it has some of the most 'on' time of them all. In my tests I found it gave nearly the same output powers as a constant 5V source (obviously testing before the scanners)
    Last edited by norty303; 06-28-2017 at 08:31.
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    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  10. #30

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    They are designed this way, and they ALL do it.

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