ELECTRONICS: FUN AND FUNDAMENTALS
By Charles Platt, Author of Make: Electronics
The Do-Not-Touch Box
Use a simple accelerometer to perplex your friends.
The price may seem high (the one I recommend currently retails for $23, which is
among the cheapest) but in the project I have
in mind, the additional parts should cost you
less than $5.
transitions in 2 perpendicular directions.
Looking down at it from directly above, when
you move it from left to right, this is considered motion along its x-axis, and the voltage at
the lower-right pin will increase momentarily.
Move it from right to left, and the voltage on
the same pin will diminish momentarily (see
Figure B).
When you push the accelerometer away
from you, and then pull it back toward you, this
is considered motion along the y-axis, creating
voltage fluctuations on the lower-left pin.
You can easily test this with just a 9V battery,
an LM7805 voltage controller, and a multimeter, as shown in Figure C. The LM7805
supplies 5V, which you connect with the 2
top pins on the mini-board. But which end
is the top end? You can compare it with the
photographs here, or look underneath, and
you should find the pins identified as X and Y
(the outputs), Gnd (negative voltage), and Vin
(positive voltage). Make sure you apply the
voltage to the correct pair of pins, the right
way around!
A Negative(ground) 5VDC power X-axis output Y-axis output
ACCELEROMETERS HAVE BECOME
ubiquitous. Your car contains an accelerometer that triggers the deployment of an airbag
if it senses a collision. The game controller
on a Nintendo Wii contains an accelerometer
that responds to your physical movements.
If you build a robot, and you want it to react
appropriately when it bumps into something
or falls over, an accelerometer can take care
of that, too.
Modern accelerometers are truly amazing,
microscopic devices, packaged inside tiny
integrated circuit chips that can cost less than
50 cents each. This kind of chip is known as
a MEMS (micro-electro-mechanical system),
and if you want to see how they work, you can
find some fascinating electron micrographs by
searching online for “mems device.”
I can imagine dozens of hobby projects
using accelerometers. The only problem is
that MEMS chips are so small, typically less
than 5mm square, that they’re very difficult
to work with. Fortunately you can buy one
already mounted with associated hardware
on a mini-board measuring ½"×¾", ready
to be plugged into an everyday breadboard.
Charles Platt
Experimenting with
the Accelerometer
I selected the DE-ACCM6G made by Dimen-
sion Engineering (Figure A). This is a 2-axis
accelerometer, meaning that it will detect
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