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Thread: Open Source Scanfail Unit (phase 1)

  1. #1
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    Default Open Source Scanfail Unit (phase 1)

    Hi all

    following on from the great thread about scan fail systems

    here http://photonlexicon.com/forums/showthread.php?t=4282

    the posibility of designing an open source Scan fail unit that could be used by most people here....could become a reality

    to start the discussion some of the things we need to look at are

    1, conditions of failure
    2, input sense requirements
    3, compatability with scanner amps on the market
    4, response time
    5, output control ( beam shutter, diode blanking or both )

    these are just a few that i can think of .... in no particular order

    if anyone can think of other important criteria please contribute to this thread

    all the best .... Karl

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    A safe window(s) would be a useful feature, so static beams and unsafe effects can still be projected, well above peoples heads..
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  3. #3
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    dave said
    A safe window(s) would be a useful feature, so static beams and unsafe effects can still be projected, well above peoples heads..
    im guessing that to accomplish this we need to make an early important decision of "do we design a microprocessor based unit or an analogue unit.... or a unit that combines both "

    all the best .... Karl

  4. #4

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    Hi Karl,

    2D safe window can be accomplished fairly simply using analog comparators (e.g. LM339) between X or Y channel signal and a preset voltage (e.g. potentiometer to set window size).

    Kind regards,

    sonaluma

  5. #5
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    also adding offset to the comparators would allow the window to be moved around the projection areas

    all the best .... Karl

  6. #6
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    Quote Originally Posted by Banthai View Post
    1, conditions of failure
    This is not too difficult. My opinion is that if the full-field scanning is slower than around 10 Hz, we consider that to be a scanning failure. 10 Hz is just a rough number, and the actual number would depend on things like "distance to the audience" and "width of the overall scan field". Nevertheless, experience has shown that 10 Hz is a reasonable number. If there are other opinions, lets hear them .


    Quote Originally Posted by Banthai View Post
    2, input sense requirements
    In my opinion, this thing should sense position. Position is available on many scanner amps, and on those that it is not directly available, it can be made available with, at most, a single resistor tie-off point. For the DT-40 and DT-40 PRO, I can tell you where to tie a 2K resistor to get a position test point.


    Quote Originally Posted by Banthai View Post
    3, compatability with scanner amps on the market
    Good one!!! Well, fortunately or unfortunately, what we see is that the vast majority of scanner amps out there are a copy of the Cambridge CB6580 design. So, with all of the amps being a copy of this one amp, it means that if we make something that works with this one, it will work with pretty much everything else out there.

    Regardless, what you have is this. All amps have a position signal (whether it is directly accessible, or indirectly accessible). So by making it work with position, that generally will make it compatible.


    Quote Originally Posted by Banthai View Post
    4, response time
    I think somewhere between 1 millisecond and 10 milliseconds is attainable and realistic for this kind of project. 1 millisecond buys you a single-pulse MPE of 10 milliwatts per square centimeter. If we have a faster response time, we start "eating into show content" and the artistic element of the show starts to suffer. Plus, it would be difficult to get better than 1 millisecond out of a simple circuit.


    Quote Originally Posted by Banthai View Post
    5, output control ( beam shutter, diode blanking or both )
    As far as I have seen, most projectors (especially those of hobbyists) do not have any kind of shutter what-so-ever. Therefore, to me, this thing has got to "blank" the color signals themselves. But that's pretty easy to do.

    And I think it is a good idea -- to the greatest extent possible -- if there are only a few, or preferably zero adjustments to this thing. It should simply work. Providing adjustments only means that there is the possibility (probability) that it will not be adjusted correctly.

    Quote Originally Posted by dave View Post
    A safe window(s) would be a useful feature, so static beams and unsafe effects can still be projected, well above peoples heads..
    Right, well... sounds like you are talking about the need of a professional to me...

    And I would like to remind everyone what we are talking about here. We are talking about a simple scan fail mechanism for hobbyists only. If you are a professional, there are already products for you. If you are making money doing laser shows, then you should have enough money to buy a professional safety system. If you don't, then I have two suggestions -- raise your prices, or get out of the business. Blunt, but serious!!

    And a few more points. Each additional component that you add is a component that can fail. Each additional adjustment that is added (especially an adjustment for fancy things like "windows") is an adjustment that can be mis-adjusted (or fail).

    As an aside, how many people have turned up the volume on your TV, radio, or computer speaker and heard the sound crackle. Well, that's an adjustment that is "failing"...

    Each additional component that is added decreases the reliability. Therefore I think it would be a good goal to keep the parts count as low as possible, with as few (or zero) adjustments as possible. As an example, I have conceived of a way of doing everything above with just two (Radio Shack) ICs and a handful of passive components, and zero adjustments. You're not going to get much more reliable and simple than that... But I am not going to just cast forth the design. This is supposed to be "Open Source" not "Benner Source". We will see how this emerges, and see what kind of design we collectively converge upon.

    Best regards,

    William Benner
    Last edited by Pangolin; 04-16-2008 at 18:59.

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    Quote Originally Posted by Pangolin View Post
    In my opinion, this thing should sense position. Position is available on many scanner amps, and on those that it is not directly available, it can be made available with, at most, a single resistor tie-off point. For the DT-40 and DT-40 PRO, I can tell you where to tie a 2K resistor to get a position test point.
    And its just a case of integrating the position to obtain velocity, well thats half a quad opamp gone.
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    Quote Originally Posted by dave View Post
    And its just a case of integrating the position to obtain velocity, well thats half a quad opamp gone.
    It's differentiating position to get velocity. And yes, half a quad. Anyone want to guess what the other half does?

    Bill

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    Opps, my bad :S
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  10. #10
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    In the interests of simplicity and not having to re-adjust the projector for every venue, how about an 'above / below horizon' solution, where the scanfail device only operates below the 'horizon'. Then, when setting the projector up in a venue, you align the horizon with audience head clearance height, thus allowing fail-safe audience scanning 'below the horizon' and aerial effects like stationary beams above the horizon. You could then design all your show frames with this in mind, with a 50:50 split.

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