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

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.

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 closer!

John :-#)#

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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 description. 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.

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?

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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.

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 :-#)#

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  (Please post followups or tech enquires to the newsgroup)  John's 
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the

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.

greg

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...

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  (Please post followups or tech enquires to the newsgroup)  John's 
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        www.flippers.com              "Old pinballers never die, they 
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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. mike

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John,

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.

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.

Arfa

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