Page 101 - 15 Dangerously Mad Projects for the Evil Genius

80 15 Dangerously Mad Projects for the Evil Genius

be flush to the wall. Adjust the laser, moving it in Although when you shine a laser on a distant
the putty until it hits as near the center of the wall at night it may seem like lasers travel for a
mirror as possible. tight beam forever, actually they don’t. The type of
Now fix the next mirror where the dot appears coherent light they use is easy to focus, but it must
on the wall opposite. Repeat this for the last actually be focused and the laser module includes
mirror, which should be attached to the wall with a a glass or plastic lens to accomplish this.
bigger bit of putty to allow it to be angled slightly Lenses are never perfect and hence the beam,
back to the control box. although very narrow, will eventually diverge. The
The control box should be fitted so the laser hits more it diverges, the more spread out the light and
the diffuser. At this point, the LED should turn off therefore the dimmer it is where it hits a small
sensor like our phototransistor.
and the alarm is successfully installed.
This is a project that requires a little trial and
error to get right. You may find that your laser is
Summary
bright enough and your mirrors good enough to
achieve more bounces over a greater distance. An improvement on the design would be to use a
bistable latch, so that once triggered, the buzzer
You may prefer not to use a mirror at all but
does not stop sounding until the alarm is reset. If
instead protect a longer region with a single beam
you search the Internet for “bistable latch,” you
pointing directly into the control box.
should find some resources and an explanation for
the adventurous reader on how to try this
Theory modification.
In the next chapter, we are going to meet an
This alarm is interesting in that it shows the
Arduino microcontroller board and use it to create
difficulty of accurately positioning a laser and
an impressive spinning persistence-of-vision effect.
mirrors. Walls are never completely flat, nor
absolutely vertical. Mirrors are not perfect
reflectors and the laser beam itself will not travel
in a tight beam forever before it loses much of its
brightness.