Project
by Dan Shanefield
Harvesting
Electricity From
This Month”s
Projects
Harvesting Electricity . .40
Capacitance Meter . . 43
Membrane Switches . 48
Blackbox Frisbee . . . . 52
The Fuzzball
Rating System
To find out the level
of difficulty for
each of these
projects, turn to
Fuzzball for
the answers.
The scale is from
1-4, with four
Fuzzballs being
the more difficult
or advanced
projects. Just look
for the Fuzzballs in
the opening header.
You’ll also find
information included
in each article on
any special tools
or skills you’ll
need to complete
the project.
Let the
soldering begin!
The Environment
Light a 100 Volt Bulb with the Waves
that Surround You
With "smart" cell phones, Wi-Fi, RFID
tag systems, and so many other
new applications for radio waves
these days, it is obvious that we are immersed
in an electromagnetic field ("EMF") just about
everywhere we go. Whether or not this is
harmful to human beings is a controversial
subject, although many scientists will tell you
it is not hurting us at the present intensity
level. However, you can easily demonstrate
that such fields can be pretty strong. At the
very least, this indicates an ever increasing
need for shielding in hobby electronics projects, to avoid picking up troublesome noise.
Because there is so much EMF in the general environment, several research projects
(mostly military) are purposely "harvesting"
the energy and trying to use this to operate
sensors, tiny transmitters, and other devices
that will never require batteries or even solar
cells. Another branch of the research aims to
use strictly mechanical noise to harvest energy from the environment, similar to the way a
self-winding mechanical wristwatch operates.
However, many useful things such as sensors
need electric power in some way, and it is usu-
ally inefficient to collect low-level mechanical
energy and convert it to electricity.
Although a radio aerial converts electromagnetic waves into electricity, the voltages
that are fed to cell phones from ferrite antennas are typically only a few microvolts. It
might be a surprise to the reader, but a million
times more voltage — possibly four volts or so
— can actually be harvested by simple means
from many common environments, by using
a fairly long antenna and a good ground. The
currents are small, but they can easily be
accumulated, enough to briefly light a
Tungsten incandescent bulb. With a transformer, these voltages can be stepped up
enough to flash a neon bulb. It's amazing, but
quite true, and all this can be verified with
experiments that are easy to do.
The Experimental Set-up
The circuit is shown in Figure 1, but it is
not necessary to use any actual switches.
Alligator clips could be used instead. For
example, looking at S1 in the diagram, a clip
lead could be temporarily connected from the
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NUTS & VOLTS
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FIGURE 1
40
FEBRUARY 2004
