cymbal sound, this is also an important part of
displaying the beat.
While developing this project, I found the app
“E-Scope 3-In-1” very useful. It’s free on the iPad
and has a signal generator that allowed me to check
the response of individual frequencies. You can also
play a 10 kHz signal into your stereo and hear what
you’re not really going to miss by giving up the
seventh band.
Lasers
First, I should say that lasers can be dangerous.
I made a small laser test circuit on a piece of
perfboard, and was using it to test a blue laser. I
had my laser safety glasses on, and was beaming it
at a block of wood while trying the focus and
brightness. Soon I realized there was smoke coming
from the wood where the laser was burning it!
If you’re thinking of a laser light show, be aware
that there are laws governing this. Permits,
variances, and certifications need to be obtained,
and the laws vary by state and country. The
regulations are for commercial use of the lasers, so
personal use is much less restrictive. If you’re using
it for friends and neighbors, it’s not being sold by
you, and it’s not used in an event where people pay
admission, then you are often free of bureaucratic
complications. The regulations aside, it’s always bad
practice to fry your friend’s eyeballs.
While none of the lasers as used in this device
will burn your skin, I imply nothing in the way of this
being safe, and you should be aware of the danger
involved. Also, use caution in avoiding looking directly at
the laser beam, and perhaps even more caution is needed
for reflection off a shiny surface that could bounce the
beam into one’s eyes. The beam should always end at a
light absorbing material or a diffusing screen, and not be
directed randomly around the room where it can hit
something shiny and reflective.
That said, there are ways to be safe. It can be made
safer by keeping the cover on when it’s in use. These
lasers are very bright, but they are throttled down in their
intensity by limiting the current. The strong blue one is
especially attenuated.
After the beams go through the glass disks, they
become stretched out to cover a much larger area, and
thus the intensity of any given spot is greatly reduced.
Pulse Width Modulation (PWM) is used to control the
intensity of the beams, and much of the time each beam
is running at a fraction of its power.
It’s feasible that through amazing coincidence, a loud
passage of music could turn on three lasers in one beam
to a stronger intensity at the same time someone decides
to look right at the laser. If a person’s eye happens to be
in the exact location that the beams are together and
intense, it could become possible for eye damage to
occur. I suggest several things to protect yourself while
setting this up. When you’re aligning lasers, set the
selector switch so that the lasers are at a very low
intensity. For operating the machine, a cover is necessary
for the lasers and disks so that no stray beams can get into
your eyes. Especially watch out for beams reflecting off of
the back of the glass disks. Since the best glass for this is
very lumpy on the outer surface and slightly wavy on the
inner surface, the inner surface could reflect some light
back at an angle in an unexpected direction.
Laser safety glasses are available. I have one pair to
block red and green, and another to block blue. You can
also view the lasers through a digital camera, as the laser
light doesn’t come through the screen — only an image of
the laser. The lasers shining off a diffused screen such as
white foamboard or the wall is not dangerous but looking
into the beam itself is. A shiny mirror-like surface can
bounce the beam directly into your eye, and mirror-reflected laser light is nearly as dangerous as a direct hit.
When working on it, place it below eye level so you
can see it with less chance of a beam going into your eye.
In the machine’s final position, if it’s mounted above eye
May/June 2018 43
■ FIGURE 5. Layout of everything, with some important
dimensions.
