■ A near space flight can climb to over 30 km, so it can
experience a significant increase in UV-B but still not
receive much UV-A. This graphic is from the Geophysical
Institute at the University of Alaska, Fairbanks.
a lunar or Martian rover can use a sun sensor to
determine directions in lieu of a compass (this is an
issue for these two locations since neither the moon or
Mars have global magnetic fields). A robot can also use a
sun sensor to determine when the sun has risen or set —
very important to a solar powered rover. If calibrated
properly, a robotic rover might also use the sun sensor to
determine the intensity of the sunlight. If you plan to use
the sun sensor in robotics, I recommend drilling out the
large mounting holes in the PCB (see January’s issue). Bolt
two-inch long #4-40 machine screws to the PCB so the
sun sensor can attach to the robot. Raise the sun sensor
on a mast that keeps it above any other structure on the
robot (to avoid shadows). (In the near future, I plan to
write an article for SERVO Magazine about an articulated
robot that uses the sun sensor in this way. So keep your
eyes open.)
NearSys is in the process of producing a sun sensor
kit for those who do not want to make their own PCB or
gather the needed components. Go to
NearSys.com/catalog for more information.
ADDING UVC TO THE
ENVIRONMENTAL TEST CHAMBER
68 May 2010
In my Nov ‘09 column, I discussed how I
incorporated ultraviolet into the simulator. However, I’m
not totally happy with this UV source (UV LEDs) because
its ultraviolet light is too close to the violet part of the
visible spectrum. As many Nuts & Volts readers know,
scientists divide the UV spectrum into three ranges:
A, B, and C. Ultraviolet A, or UV-A, spans a wavelength
range from 400 to 315 nm — this is the band of UV
■ A $10 source of
hazardous ultraviolet. Just
the thing for the near space
environmental test chamber
on a budget. Do not look at
the UV from these lamps.
emitted by the
affordable UV LEDs in
my environmental
chamber. Of the remaining
two bands, UV-B spans
from 315 to 280 nm and
UV-C spans from 280 to
100 nm.
UV-A from the sun
reaches the surface and is
not usually considered very
dangerous. However, it can
cause indirect damage to
our DNA (via the creation
of free radicals, or highly
reactive molecules). Too
much damage can lead to
cancers. UV-C is the just
the opposite — it’s known
to be extremely hazardous.
Fortunately, it’s blocked high in the stratosphere. Ozone in
the stratosphere strongly attenuates UV-B, but some still
reaches the surface. The small amount that does make it
to the ground promotes the healthy production of vitamin
D and is responsible for the sunburns we get each
summer.
To improve the quality of my near space simulator,
it needs to have a source of UV-B. LEDs capable of
emitting this frequency are commercially available, but
are too costly at this time. UV-C, however, is used as a
germicide and is readily available in items like water
purifiers for backyard ponds. Since I can’t get an
inexpensive source of UV-B yet, I decided I’d settle for
mixing some UV-A and UV-C (am I right in thinking that
mixing UV-A and UV-C averages out to UV-B?). Actually,
I initially thought I had found a good UV-B source when
I ran across the UV source described this month. It
wasn’t until after I had installed the lamps into my
environmental chamber that I discovered they were really
UV-C. Therefore, here’s my experience with adding
another ultraviolet source to my environmental test
chamber. Readers may find other uses for this inexpensive
UV-C source.
The Den Tek toothbrush sanitizer is a plastic case
containing batteries, an ultraviolet lamp, drive circuit,
and power switch. The drive circuit boosts the voltage of
its two AAA batteries to the 470 volts peak-to-peak it
takes to operate the UV lamp (which is an uncoated
mercury vapor lamp). So, let’s violate another warranty by
bashing this commercially available product into
something more useful.
To gain control of the UV lamp, you have to open the
