Wall Eye

Wall Eye:
Build your own opaque projector
Steve Lodefink | Make Vol. 14- 2008 | Pdf | 5 pgs | 2 mb

What's an opaque projector? You know, one of those contraptions that takes
flat, reflective subjects such as printed pages, leaves, or coins, and projects
them onto a screen or wall. Opaque projectors were common classroom
presentation tools during most of the 20th century.

Although made largely obsolete by the use of video cameras coupled to video
displays, opaque projectors are still being made and sold. Marketed today
mainly to art students and hobbyists for use as drawing enlargers, entry-level
models tend to be dim little plastic toys that can only accommodate puny 3" or
4" originals, and have to be used in a totally darkened room due to their small
apertures and weak light sources. If you're lucky enough to find one of the
majestic 1,000-watt giants from yesteryear at a swap meet, then consider
yourself charmed. I was not so lucky.
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Safety Spectrometer

Safety Spectrometer
Eric Rosenthal | Make Vol. 14- 2008 | Pdf | 2 pgs | 1 mb

After air travel security banned bottled water and
baby formula, I began wondering why they didn't
use a device to determine the contents of liquids. If a
liquid was detected to be safe, security could allow it
on the plane. Spectrometers can identify the chemi-
cal makeup of a material by shining light on it and
analyzing the precise mix of colors that bounce back.

These devices are usually very expensive, but
I've designed a simple and inexpensive one that can
identify liquids. You can also adapt it to determine
the color of a swatch of paper or cloth or to identify
a gem or semiprecious stone.

I spent less than $100 on this project and it took
just a few days to design, fabricate, and test the hard-
ware, plus another two days to write and debug the
source code. Collecting the liquids and building the
database took one evening, and it was fun!
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Gardner's Mathemagic

Gardner's Mathemagic
Donald E. Simanek | Make Vol. 13- 2008 | Pdf | 4 pgs | 1 mb

The Gilbreath Principle

A number of card tricks are based on a principle that
magician Norman Gilbreath introduced to magic. It's
an application of combinatorial mathematics (which
we will spare you here). Gardner discusses it in
his books New Mathematical Diversions from
Scientific American, Chapter 9, and Mathematical
Magic Show, Chapter 7. We'll describe here the
simpler versions.

Prepare the deck ahead of time with the cards in
black/red alternation. No other order is necessary.
When you start this trick, you can do any false shuffle
that doesn't change the card order. But if you don't
have those skills, don't bother.
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Make Vol. 13- 2008: Do It Yourself

Make Vol. 13- 2008: Do It Yourself
Pdf | 31 pgs | 12 mb

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Purely Platonic

Purely Platonic
A dodecahedron table lamp
Charles Platt | Make Vol. 11- 2007 | Pdf | pgs | mb

People appear symmetrical, but even the most
perfect human face shows irregularities if we
compare the left side with the right. Perhaps this
is why the absolute, rigid symmetry of crystals
seems beautiful yet alien to us. Unlike DNA's
soft spiral, a crystal's molecular bonds align
themselves to form regular three-dimensional
structures.,which the Greeks considered math-
ematically pure. The most fundamental of these
shapes are known as the five Platonic solids.

If you assemble equal-sided triangles -- all the
same size, with the same angles to each other --
you can create three possible solids: a tetrahedron
(with 4 faces), an octahedron (8 faces), and an
icosahedron (20 faces). If you use squares instead
of triangles, you can create only a hexahedron,
commonly known as a cube. Pentagons create a
dodecahedron (12 faces), and that's as far as we
can go. No other solid objects can be built with all-
identical. equal-sided, equal-angled polygons.

The Platonic solids have always fascinated me.
My favorite is the dodecahedron. which is why
I used it in this project as the basis for a table lamp.
By extending its edges to form points, we make
something that looks not only mathematically
perfect, but perhaps a little magical.

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