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What Could You Do With 120 Laser Pointers?
lazed-dazed asks: "I've recently come into possession of a large number (120 of 'em) of keychain laser pointers (minus the fancy diffraction adapters, though the specs are the same). So, Slashdot, I ask you: Can you give me any project ideas for these low-wattage bad boys? Holograms? Fancy cigarette lighters? Laser cannons? The crazier, the better! Oh, and don't bother suggesting cat toys."
If there is a quicker way to get yourself shot, I don't know of it.
The whole point of a laser is that all the photons emitted from it are in phase with each other. The photons emitted from one laser are not necessarily in phase with those emitted from another laser. Thus, while you might be able to get .6 watts out of these lasers, it wouldn't be anything near like having a .6 watt laser. And it definately would be too bulky to mount on the head of a friggin' shark.
As a matter of fact, Texas HB-831 has made it a class-C misdemeanor
"Person commits a class C misdemeanor if they knowingly direct a laser pointer at a police officer, uniformed security guard, fire fighter, emergency medical service worker, or other uniformed municipal, state or federal officers. "
Apparently for fear that a police officer would confuse a laser pointer with a laser sight from a gun.
I did this once. A cheap radio shack photocell tied to +5 volts via an active output pin on your parallel port, with the other end of the photocell going to an input pin on that same port, will cause that input pin to read 0 when little or no ambient lighting is present. When hit by a red laser pointer the resistance across the photocell is lowered and the voltage at the input pin ramps up above the binary threshold, to more than ~0.8 volt but less than 5 volts. Because of this, reading the input pin from software when the photocell is lit by a laser beam shows a binary value of 1. To avoid false alarms from stray light, I housed the photocell in a sealed, opaque box with a hole in it for the laser beam to enter and hit the photocell.
A simple C program that reads and writes the memory address of the parallel port can detect, log, and act on these "laser trip" events, doing something as simple as beeping, or as complex as taking a picture and asking for a code. The program should write a 1 to the bit that controls the output pin you are using so that +5 volts appears on it. It should then repeatedly read the input pin you are using. When the input pin transitions from 1 to 0, even for a moment, you know the laser beam has been cut.
The quick and dirty C code to do parallel port operations under linux can be found at here. For beginners I suggest you use one of control bits/pins as your output and one of the status bits/pins as your input. The data bits/pins are bi-directional and must be configured for input or output, and using them makes things slightly more complicated. If you want to get really fancy try using the parallel port IRQ to detect the transition from 1 to 0, this should save processing power by avoiding an expensive loop to check the state of the input pin constantly.
If you need a little more background on the parallel port before diving in, check out this resource
Finally, the above description is for a single laser beam. I used a mirror to bounce a single beam around, to get greater coverage, and to provide the effect of multiple beams in the presence of aerosol or powder. You should be able to support thirteen independent laser beams on a single parallel port, using the data bits/pins and the status bits/pins combined.
In California it's a felony to aim a laser pointer at an aircraft.
Laser pointers can blind pilots.
I would turn them all on at once and aim them at the moon and see if you can get it to explode! Just make sure you don't hit any aircraft.
Have fun!