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photoflash circuit

Discussion in 'Electronic Design' started by kell, Jan 27, 2005.

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  1. kell

    kell Guest

    I'm going to build a circuit that flashes a strobe rapidly. If anybody
    would like to know why, look up "dreamachine." There was an article in
    the New York Times recently about it. The classic dreamachine uses a
    motor and rotating cylinder with a light bulb in it to flash at 10 Hz,
    but it will be much easier just to use a strobe.
    I just need to know the voltage and the joules for each flash of the
    strobe so I can build a circuit. I may use this bulb:
    Open to suggestions for better strobe bulbs in terms of durability,
    because the device I build may go through hundreds of thousands of
    flashes in its life, perhaps millions. But mostly I need to know
    required voltage and energy per flash for the example flash tube, or
    flash tubes in general.
  2. Si Ballenger

    Si Ballenger Guest

    You may want to look at modifying the guts of a disposable flash
    camera. I've found info on mods using google.
  3. Mike Fields

    Mike Fields Guest

    Something to check out -- seems to me that is somewhere around
    the frequency that can trigger epileptic seizures in people who are
    susceptible. Not sure the exact frequency, but it seems it is around
    8 or 10 Hz.

  4. Jim Yanik

    Jim Yanik Guest

    Doesn't Radio Shack sell something that does this?
    You hook it to your stereo and it flashes the strobe with the music.
    Probably can get one at Spencer Gifts,too.

  5. I should imagine you could make one much easier (and more adaptable) using
    some superbright white LEDs instead. Alternatively you could just look at
    this dude's website which makes your monitor function as a "dreamachine".

    It doesn't seem too particularly work for me. All it succeeds in doing is
    making a pesky/annoying flickering sensation.

    If you still want to make one using a Xenon strobe, then surely Don
    Klipstein's website will be of interest if you haven't read all of it

    The tube you linked to doesn't seem very generous with the technical
    specifications. But based on it's apparent size and just pulling rough
    numbers from thin air I should think somewhere around 350V at an energy of
    around 200mJ per flash would probably not be too outrageous. This would
    suggest a capacitance of around 3.3uF. At 200mJ the flash will probably be
    very wimpy (maybe even wimpier than what can be achieved with a few good
    LEDs), but if you go too far above this at 10Hz, the lamp will probably get
    rather hot. A quartz flashtube would be better suited.
  6. Fred Bloggs

    Fred Bloggs Guest

    Perkin Elmer bought Heimann Opto thirteen years ago. The AllElectronics
    part *looks* similar to this- these tubes are not designed for 10Hz: 2640.pdf
  7. Al

    Al Guest

    Yes, pilots have been know to experience this when the strobes flash
    back from the rotating propellers. Some people may have a latent
    susceptability to it. The frequency has to match the alpha wave of a
    susceptable person.

  8. Glen Walpert

    Glen Walpert Guest

    The spec on these is 40% output reduction in 5000 hours @ 4 Hz with
    nominally 20 joule flashes, so IIRC you should get about the same life
    at 10 Hz with 8 joule flashes, maintaining the same average power.

  9. Well... Something doesn't quite compute. The Perkin Elmer device claims a
    nominal maximum operating power of only(!) 30W. Considering it's size 30W
    is still very impressive in my mind. I guess at high flash energies almost
    all of the energy gets lost as radiation (visible and mostly infrared I
    guess) so it doesn't directly heat up the glass. I would imagine at much
    lower flash energies xenon is a less efficient radiator (and perhaps a
    higher percentage of the energy would be wasted heating the electrodes), so
    more heat would have to be convected away rather than radiated. So perhaps
    some further derating is justifiable.

    Suppose 15W average power, 350V flashes, 10Hz. Then each flash is 1.5Joules
    for a capacitance of around 25uF. 1.5J flashes would be quite decently
    bright. At 10Hz an aluminum electrolytic capacitor would be less than ideal
    given their high ESR and low ripple current rating. Ideally one would use a
    Mylar or oil filled, or similar type of low ESR high ripple current rated
  10. Glen Walpert

    Glen Walpert Guest

    Right you are, I was a bit hasty reading that data sheet.

    The constant avarage power for the same tube life at different flash
    rates is only approximately true and only over a limited range, the
    additional derating is a good idea. But I think the limiting factor
    near rated power levels is less likely to be heating than electrode
    erosion; the evaporated bits of electrode will deposit on the inside
    of the tube both darkening it and trapping Xenon gas in the deposits,
    reducing the tube pressure. Both of these effects gradually reduce
    light output with constant electrical power input. Lower power
    flashes will evaporate less electrode material per flash, in a very
    roughly linear manner over some limited range of power near the tube
    data sheet ratings.

    This is per my recollection of data on high power laser pump flash
    tubes (where feedback is often used to maintain constant light output
    as the tube ages, up to a limit of course). I see no reason why the
    little photo flash tubes should be different in this regard, although
    that does not mean that some good reason does not exist :).
  11. Rich Grise

    Rich Grise Guest

    What about those strobes from the psychedelic '70s? They maintained at
    least a 10 Hz flash rate, and lasted for quite some time.

    I seriously doubt if they put a whole joule through the thing for one

    Good Luck!
  12. Al

    Al Guest

    You want strobes? Try small airplane strobes. You can get blinded by

  13. Is that really a selling feature? Something tells me that the OP doesn't
    want to be blinded...

    Generally speaking though aircraft stuff easily costs ten times what it
    seems it aught to cost due to special reliability requirements and the FAA
    and whatnot.
  14. Graham Orme

    Graham Orme Guest

    Another thing to check out is the level of UV produced. A lot of Xenon
    lamps produce wavelengths down to around 200 nm and come with a warning
    not to view them with the naked eye.
  15. Al

    Al Guest

    If you want power, why screw around.

    And the cost was not bad, $160 or so. And it will be reliable.

  16. kell

    kell Guest

    I bought this:
    It comes with a circuit diagram. Shows a voltage doubler off the 120
    volt ac power line, with 22 uF caps. There is another .47 uF cap that
    charges up through a pot (for timing) until it fires a neon bulb that
    turns on an SCR connected to the triggering coil; and the 22 uF dumps
    into the strobe. I have to get a neon bulb and an SCR before I can
    build the circuit. I have some hi-com (three quadrant) triacs if I can
    figure out how to use one of them in place of the SCR. In that case
    it's just a trip to Radio Shack for the neon bulb and I can build my
    Funny thing, the parts list specs the 22 uF caps as 315 volts, when
    they should be seeing 340 volts from the doubled peak line voltage.
    Fortunately I have some 450 volt 22 uF caps.
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