●●●●
This unique DIY
construction project
blends electronics
technology with
subtle magic and
hand craftsmanship.
This concluding part
examines the theory of
operation, installation
and assembly, testing,
and verification that the
design works properly.
It also presents
mini-tutorials on Hall-
Effect and magnetism.
This allows you to more
fully understand and
appreciate this project.
THE MYSTERIOUS
MAGIC
BOX
Part 2
Carefully follow these instructions to avoid any problems
with sensor alignment, soldering
bridges, and proper placement of
deliberate shorts on the PC board.
We’ll help you recognize the differences in component selection and
placement in the two kit versions
which are available for purchase, for
your convenience.
advantageously exploits magnetism.
Magnetism and
the Hall Effect
■ FIGURE 1. The Hall effect phenomenon
of charge accumulation on the conductor’s
edges under the influence of a current
source.
Sometimes we take the simplest
things for granted that profoundly
influence us. In this project, it is
magnetism and the Hall effect that
(a)
The Hall Effect Phenomenon
When an electric current flows
through a conductor in the presence
of a magnetic field, the magnetic
field exerts a transverse pressure on
the moving charge carriers. This, in
turn, pushes these carriers to one
side of the conductor. This is most
conducive and therefore prominently
occurs on thin, flat conductors. As
the charge accumulates on the sides
of the conductor, it balances this
magnetic influence. This produces a
measurable potential or voltage
between these two sides. This phenomenon is known as the Hall effect.
Edwin Hall — a 24-year-old
graduate student at Johns Hopkins
University — discovered this in
1879. He experimented with a thin
sheet of gold foil on a glass plate
(later, he used other materials) and a
current source (see Figures 1a and
1b). He tapped off the gold leaf at
different points down its length and
noticed the varying potential.
(b)
46
May 2007
