Fake Laser Rifle

[efkaefka]

Hello:<p>I occasionally do a Mister Science show at the local grade school and need to add some new "Experiments" to my portfolio. Have already done the Liquid Nitrogen (I am a chemist by trade), chemical indicators, Gak, and the standard chemistry related stuff. <p>For my new "experiment", I want to use a laser level as my laser beam and fire it through the fog created by dry ice/water so the kids can see the beam while simultaneously
pressing some sort of transmitter (probably not IR or laser) which will trigger a relay and fire a small amount of smokeless powder about 20 feet away. Have thought about these small 900 MHz units seen in N&V but don't know what to do next.
Anyone have any experience in assembling a rudimentary transmitter to generate a pulse for a few seconds?

[Mike]

If I understand correctly, you need it so that the laser hits the 'target' and fires the powder. I would suggest a photoresistor connected to a 555 monostable timer as the trigger. set the length of the timing to however long you need, and then connect a relay to the output and ground. That should give you the relay pulling down for however many seconds after the laser beam hitting the photoresistor. It may be helpful to connect a potentiometer inline with the photoresistor and pin 3, to adjust sensetivity to room/natural lighting. The problem, though, is I believe the 555 needs to be reset once triggered. To do that, connect a NO pushbutton from the reset pin to the 555's ground. I don't know the equations for figuring time delays, but refer to the datasheet for the 555 at www.national.com for the equation and scheamtic.<p>-Mike

[josmith]

YOu can get single channel radio controlled toys for very low prices. Some have a relay output. Others run the motor directy but should still be easy to hook to another output.

[Riptide]

Hi Dave,
Why not try this:<p>http://www.radioshack.com/product.asp?c ... 980%2D0201<p>This would be a quick and simple solution for you
since you are a chemist and might not want to take the time to learn to build your own circuit right now. Be aware that the output of the wall module is 120 volts AC, of course.
You can simply hookup a relay with a 120 vac coil and use the relay to switch a safer low voltage source (battery) to ignite your pyro charge.
Just a suggestion, good luck.
RT

[Chris Smith]

Use painted black tubes or straws on the inlet to your photo transistor to block out the ambient stray light. The longer they are the more they cut out the stray. If you bias a photo resistor and relay, no 555 is needed. About 20 years ago I did the same thing, only I did it at night with lots of chems in my black powder to give all the pretty colors. Red phosphorous and per chlorates as well as magnesium made very impressive bangs with lots of light as well, with out having to contain the powder. The light could be seen for miles, and you were blind for hours if you stared directly at it? The fun part was hitting the powder pile at over a mile away and You Knew when you hit the target.

[weworkforgod]

Get one of the little key chains that have a button that send a signal that buzzes on the keys (so you can find the keys).<p>You are going to have legal problems with the explosive in a classroom. This isn't 1960. In this day and age all sorts of "class c fireworks" laws have been ennacted.<p>I recommend you purchase "cigarette loads" which are harmless. Go to the model rocket shops and use super-glue to attach an electrical igniter to one of the cigarette loads. Hook up a dry cell or two. You get a harmless explosion. If you want a bigger harmless explosion, get a 35mm plastic film container and make a hole for the wires in the top. Put your cigarette load igniter on the cap. Then drop no more than two-three drops of lighter fluid in the container (not getting the igniter wet.) Vodka will work too. Play with the stoichiometric ratio. You want to tip the container from side to side to allow the fluid to disperse if you use lighter fluid. You could also get a tube of bangsite from the Big-Bang company and use calcium carbide and a bit of water in lieu of the lighter fluid. The Bang-site works very well and in a litigenous society you won't have anyone discussing your possession of explosives.<p>[ July 29, 2003: Message edited by: experimenter ]</p>