Page 92 - 15 Dangerously Mad Projects for the Evil Genius

Chapter 6 ■ Touch-Activated Laser Sight 71
Figure 6-10 The wiring diagram
If everything is all right, we can glue the laser Not that long ago, lasers used to be something
module and terminal strip into place. Use only a
small amount of glue so the laser module remains
flush with the corner of the box.
Step 5. Finish Up
We can now attach the touch sensor leads to the
terminal block and attach the box to the side of the
gun. Adhesive putty is a good non-permanent way
of attaching the box to the gun. It also allows the
angle at which the laser shines to be adjusted a
little so it is in line with the gun barrel.
That’s it. A nice simple project.
Testing and Calibration
Trial and error is the best way of calibrating the
laser. Fix the laser in one position and then fire the
gun, noting the position where you hit the target
and tweak the laser toward that point.
The laser will never perfectly light up the place
where the pellet will hit for a number of reasons,
not the least of which is that BB guns do not shoot
very straight. And most especially, if shot over a
distance, the trajectory of the pellet will be falling,
whereas the light from the laser is immune to the
effects of gravity.
Theory
The key components of this project are the laser
diode and the FET transistor. We now take a
detailed look at these two componets.
Laser Diodes
The word laser was originally written as LASER
because it stands for Light Amplification by
Stimulated Emission of Radiation, but these days it
is just written as “laser.”
you only found in laboratories. They create a beam
of light at exactly one frequency (color). They also
have the property of coherence, which means that
all the waves of the light are in step and don’t
overlap each other. This makes it possible to use a
lens to focus them into a very narrow beam that
remains a small dot even when aimed at something
quite distant.
Lasers have become cheap and easy to obtain
because of the laser diode, which is a similar
technology to regular LEDs but generates laser
light rather than ordinary incoherent light. These
are used in CD and DVD players.