Circuit design wanted - LED Strobe

Discussion in 'The Projects Forum' started by Karl Yeager, May 7, 2015.

  1. Karl Yeager

    Thread Starter New Member

    May 7, 2015
    2
    0
    I am wanting to have a circuit designed for me. This may not be the forum for this so first let me ask if there is a website where you can give your particular specifications and have a circuit designed? What I am looking for is an LED strobe effect circuit. The strobe must have a very fast cut off time so there is very little tailing. I want to completely stop (turning a little clock-wise or counter-clock-wise is fine) the rotating image at 1000 rpm so that you can actual see the image. I understand if you were looking at a multi-blade fan with one red blade that the red blade will be in different spots of the rotation since the timing of the rotation of the blades and the timing of the strobe will not be the same, I just want it to appear stopped. I have tried store bought "fun" LED strobes and they blur the image very badly. I have built the typical 555 timer circuits I have found posted and they also tail bad enough that the image is pulled and not clear. If I use a classic xenon strobe is looks perfect but I want to use LEDs.

    This sounds easy until you try to get the strobe to turn off fast enough to not blur the image. I read that some white LEDs use a phosphoring additive that could be causing the slower dimming effect. I am willing to pay $200 for a working circuit with specified LEDs and can be reached at my email (MOD NOTE - E-MAIL ADDRESS REMOVED)
    I did not read anything in the terms and conditions that forbade asking for this sort of service but if I am out of line I do apologize.

    What I would like:
    • Fairly simple circuit that runs on either one or two 9volt, 3 AA or multiple AAA batteries @ a strobe of 2hz with a run time of 4 hours per battery(s) change
    • Circuit described above capable of supporting 6 fairly bright clear LEDs (Needs to be bright enough to read writing on 1000 rpm rotating device in dark of course)
    • Needs to make 1000 RPM rotating object appear completely stopped not blurred or pulled
     
    Last edited by a moderator: May 7, 2015
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    There is a reason that xenon strobes work better than LED.
    Max.
     
  3. WBahn

    Moderator

    Mar 31, 2012
    17,748
    4,796
    MOD NOTE: I removed your e-mail address from your post -- otherwise you will start getting spammed by the folks that vacuum websites for e-mail addresses (it might already be too late).

    Use PM (Private Message or "Conversations" as they are called here) to exchange e-mail addresses if you get to that point.

    I'm not aware of any prohibition to trying to find someone to do a small job for you, but most folks here will give out advice and ideas for free but aren't interested in doing work for hire like this. But some are and you might find someone.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    To have no bluring , flash time needs to be 0; so we need a comprimise. Say a rotating cylendar about 3 in dia. rotating at 1000 RPM, then surface is moving about 17 ft. / sec. Say we allow .01 in. smear, then flash could be about 50 usec.
     
  5. Karl Yeager

    Thread Starter New Member

    May 7, 2015
    2
    0
    Thanks for narrowing down the flash time. The diameter is closer to 18", just think of a fan with blades and I want a stop image of the fan twice a second. When I used a fixed rate xenon strobe I was able to see a complete stop image at any speed right up to 100o RPM, actually faster than 1000 RPM but not really required.
     
  6. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi Karl,

    Just give a particular specification here, but stay within sane and possible values - we're very friendly here, but we won't stop the time for just anybody ;)


    This is exactly the reason why I won't take jobs like this.
    In engineering we need absolute values, not subjective adjectives like "very fast", because then we could debate forever over what was "very fast" and the risk is, that the customer is never satisfied, so, lots of work and no pay.

    Further is the often seen lack of realism about what's possible on a small budget ($200 is an hour of design/consultancy in my book) and even what's possible with unlimited funds, but within the boundaries of the Laws of Nature.

    The lack of information is another hurdle and when customers are secretive about the purpose of what they want, it's like flying blind in a thunderstorm - working with a wing and a prayer.

    Why on earth don't you want a xenon strobe? They've got the second fastest flash obtainable (THE fastest on a budget), as they're low impedance discharge devices.
    Is it a size issue (they can be made very small)?


    Nah, it's not the phosphor -, that could be solved by just using a high power colored led like cyan blue green or red (depending on colors of the observed object or a blend a red, a green and a blue).
    What you've seen is just the effect of sloppy switching paired with the capacitance of the LEDs - but that's not an issue in toys.


    "Fairly simple" is what goes into the toys that you've already tried and didn't like, so perhaps opt for slightly more complicated.

    A 2Hz strobe? I bet you're secretly aiming at opening a discotheque for senior citizens ;)
    Seriously... To make 1000 RPM appear stopped, you need 16-2/3Hz (16.7Hz rounded) or a division of that, like 2-7/9Hz or 1-7/18Hz - with 2Hz, the visual image will drift (appear rotating or, at that frequency, rather appear stepping it's way through the rotation).
    So, either you want it to be stopped, OR you want a 2Hz flash frequency - impossible to get both.

    A 4 hour run-time should not be a problem on 3 AA-cells, but with the voltage drop of a white LED (approx. 3.6V and higher when run how they need to be run in your application) and the fact that battery cells are specified down to 0.9V (some manufacturers use 0.8V as their flat line reference!) you wouldn't ever use them up. with 4 cells you get closer to spending all their available power. So, 4 AAA's will be more cost effective than 3 AA's only problem is, that you'd probably get way more than 4 hours on a set, say 40+ hours and that really throws off your specification :D

    "Needs to make 1000 RPM completely stopped"... That depends on: The state of your eyes, your definition of "completely stopped", the velocity of the part you wanna inspect (the longer away from the center of rotation, the higher the velocity) and your definition of blurred (not sure what you mean by pulled(?)).

    In the above, I assume that you're not trying to get the intensity of a xenon tube.

    About using a stroboscope: The flash frequency should be made variable, so that you dial in a steady image. If you need to turn the image upside down or just to a different position, you adjust the frequency slightly, to let the image rotate to the wanted position, where you readjust the frequency until standstill.

    Timing stroboscopes, as used to adjust ignition timing on cars and motorcycles, are triggered by a pickup (usually inductive) placed on a spark plug wire (on cyl #1 usually), so you don't have any frequency setting to mess with on those.

    If your application has got a trigger output of sorts, you may be able to dispense of any frequency control and use it like a timing strobe.


    If you seriously want to hire someone, do specify each parameter without resorting to adjectives, describe your project in detail and don't put up the amount that you're willing to spend. It will just attract those who can't and keep the able at bay - if you describe it in enough details, a pro will tell you the price anyway and then you can decide to go on or fold and knowing your budget, any hustler could easily convince you to double the amount.

    I'll stick to make you fold by giving you an estimate of $600 to $1200, where the total time to delivery would depend mainly on the delivery time of a specific LED obtainable for you as well.

    So, save a good wad of greenback by doing some of the work yourself and jot down objective measurable numbers and describe the purpose to get free help here :)
     
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