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Design problem - need bright flash of light for pistol game...

Discussion in 'Electronic Repair' started by John Robertson, Jun 5, 2007.

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  1. Hi Folks,

    I'm fixing up an old light beam activated rifle gallery and want to
    convert some IR Laser diode Colt-45 style pistols to a white light LED
    or possibly tiny photo-flash tube.

    The targets all work on visible light and use CDS cells (are these
    being banned?) as the sensors.

    What I have been toying with is using a 60,000LCD(?) white LED as the
    light source but I'm having trouble focusing the light so that it is no
    larger than about 6 - 8 inches in diameter at twenty feet. I'm not an
    expert on using lenses but the flash tube version of these use a metal
    shield with a small hole - I suspect to act as a point source of light
    - then the lens is about six inches away. This produces a nice bright
    flash at the target distance.

    My problem is I can't FIT a flash tube in the barrel of the pistol! Ths
    smallest flash tubes I can find are used in disposible cameras but do
    not work well as there is not much light coming out the ends - the
    elements are in the way. Can't bend them into a "U" shape as they would
    simply collapse once heated enough to soften the glass.

    The smallest u-shaped strobe tubes I can find are just over 1/2 inch
    wide and the barrel is only 1/2 in internal diameter - won't fit!

    So, I'm thinking I need to find out a couple of things - first; can a
    high intensity LED but over driven, repeatedly, on a very short duty
    cycle? And second; how the heck do you focus the bugger to something
    resembling a small - but intense - circle of light at twenty feet (6



    John :-#)#
    (Please post followups or tech enquires to the newsgroup) John's
    Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call
    (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) "Old pinballers never die, they
    just flip out."
  2. James Sweet

    James Sweet Guest

    What's wrong with the original setup?

    Does the light have to be white? If not then how about a laser diode?
    Another option would be to use a white LED to make a visible flash, but have
    an IR source be the actual trigger.

    CdS cells are still widely used, mostly for lighting control though, they're
    a bit slow for other things.
  3. The IR laser does not set off the CdS cell. They need a longer flash
    (or shorter frequency of light) than the laser provides, plus the laser
    is way too precise for my customers. This is an amusement gallery and
    they do have to be able to hit the targets on average. So the beam is
    around 4 - 6 inches across at twenty feet.

    The reason I'm trying this is simple, I'm cheap. The new photoflash
    pistols (look like toys) are almost $400US and I have ten of the Colt
    style laser pistols sitting idle that look way cooler... but they do
    not work with the CdS cells...

    I have just found some info on Luxeon LEDs and some lens systems they
    work with that gets me down to 9 degrees of dispersion... getting

    John :-#)#
    (Please post followups or tech enquires to the newsgroup) John's
    Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call
    (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) "Old pinballers never die, they
    just flip out."
  4. whit3rd

    whit3rd Guest

    There's three tricks used to make light receivers that don't get
    fooled. Filters (only allow IR in, and visible light doesn't cause
    a false trigger), modulation (TV remotes all modulate at 40 kHz,
    and the receiver is tuned for that modulation), and fast-rise-time
    triggering (common in slave strobes for photography).

    It sounds like you have the fast-rise-time triggering scheme.
    CdS can turn ON faster than it turns OFF, so that fits the
    If the original sources were really laser diodes, it's unlikely
    visible LEDs will work as well (you'll never get as high intensity
    with lenses). If, on the other hand, they were pulsed IR LEDs,
    like in laser-tag gizmos, you have a pretty good shot. In addition
    to LEDs, you can consider wink-light technology; a plain incandescent
    lamp can take nearly double the rated current, run VERY bright,
    if you limit it to a couple of milliseconds.

    It's possible your CdS cells are tuned for the wavelength of the
    IR original source; if you were willing to replace 'em with something
    else, it could ease the visible-light brightness requirement.
    My physics handbook shows CL-402 material best at 5000 Angstroms
    (yellow) and CL-404 material best at 7000 Angstroms (deep red).
    Alas, CdS is out of favor, you might find Clairex has few standard
    formulations currently commercially available.
  5. Keep in mind that laser diodes have the nice ability to be collimated
    quite well with a small lens.

    And flashlamps have the nice ability to produce a high peak light output.

    LEDs have neither. :( :)

    Why do you want to change it?

    --- sam | Sci.Electronics.Repair FAQ:
    Repair | Main Table of Contents:
    +Lasers | Sam's Laser FAQ:
    | Mirror Sites:

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
  6. mc

    mc Guest

    CdS peaks at about the same wavelength at human vision. You are correct in
    thinking it doesn't see infrared. Silicon sees infrared very well.
  7. I have been unable to find a small enough flashlamp to fit in the
    barrel, light bulbs are fragile (filament), and lasers - well I'd have
    to replace ALL the targets with new optos (there are almost 100
    targets) and that would take a lot of time!

    White LEDs appear to be almost bright enough if using the lens systems
    such as provided by L2Optics etc., these focus down to 9 degrees of
    dispersion and this could be further collumated with a small lens -
    perhaps producing enough light to trigger the cells reliably. Plus the
    LEDs have a high output when used in pulse mode - which is what these
    guns do - roughly 1msec light pulse.

    I have found a smaller Xenon "U" flash tube that might fit in the gun
    if I hollow out the bullet chamber - that is my next step. It is
    simpler than using the LED etc, as the system is already set up to fire
    photo flash tubes, 300VDC plus 4KV trigger pulse for the rifles.

    The laser is ideal, but not going to set off the targets as they
    currently are (CdS cells).

    John :-#)#

    (Please post followups or tech enquires to the newsgroup) John's
    Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call
    (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) "Old pinballers never die, they
    just flip out."
  8. g

    g Guest

    Have you tried just a pinhole with a bright LED?

    Suddenly my Google is not Firefox compatible with its visited links
    not changing color. They got to stop fooling around.

  9. Yes, not bright enough so far... need to use a lens to capture as much
    of the LED light as possible so the result has a chance of being bright
    enough to set off the CdS cell at twenty or so feet distance operated
    in the shade...

    (Please post followups or tech enquires to the newsgroup) John's
    Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call
    (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) "Old pinballers never die, they
    just flip out."
  10. mike

    mike Guest

    back in the old days, some arcade games used incandescent lamps.
    They discharged a cap across the filament. You can geta LOT of
    light that way. Life is shortened, obviously, and may not be
    good enough for a commercial arcade, but worth an experiment.
  11. ABLE_1

    ABLE_1 Guest


    This may be a little bit hokey but for experiment purposes get a cheap set
    binoculars. Aim you light source thru one of the lens. See what kind of
    spot you get at your 20'. If you are lucky enough and it is satisfactory
    disassemble and see what kind of lenses are being used which may point you
    in good direction. BTW try the light from both sides of the binoculars.
    Just a thought and may prove helpful.

    Good luck.
  12. Arfa Daily

    Arfa Daily Guest

    I know it's potentially a lot of work to replace the sensors, but you might
    be interested in some new devices from Avago that one of my suppliers sent
    me an e-flyer about today. Says that they have a similar spectral response
    to the human eye, so would match the CdS cells currently in there pretty
    well, but may well be enough more sensitive to allow you to use a less
    intense light source such as a superbright LED. Worth a look.,1339014,9613854

  13. m kinsler

    m kinsler Guest

    I've read through this thread, and the best suggestion I've seen has
    been the pulsed tungsten-filament lamp, which is usually quite
    straightforward to implement. Most miniature lamps will take a great
    deal of physical abuse.

    You might, however, wish to try fooling with the optics on the LED
    you've been trying. The dome of the LED acts like a lens, and it's
    possible that by filing it off flat and then polishing it back to
    transparency you'll be able to change the beam into something that can
    be more readily focussed by the lenses you're using. White LED's
    don't have the world's greatest spectrum, but they might conceivably
    kick over a CdS cell. Those Radio Shack stores that still sell parts
    will sell you CdS cells--I think they're still selling the assortment,
    in fact, but just a single one will help you experiment. Just hook
    the cell across an ohmmeter.

    M Kinsler
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