SCIENCE DIY

SCIENCE

SAFETY SPECTROMETER

Device identifies dangerous liquids by analyzing light. By Eric Rosenthal

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 chemical 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 hardware, 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!

MATERIALS

Arduino board from sparkfun.com. Use the Arduino NG or the latest USB version, the Arduino Diecimila.

LEDs ( 5) blue, green, yellow, red, and infrared Infrared (IR) phototransistor

¼-watt resistors: 220Ω ( 5), 1KΩ ( 2), 2.2KΩ, 18KΩ

Serial display I used a Crystalfontz 634 Serial LCD; you could also use the Matrix Orbital LK 204-25, or similar products from seetron.com.

Power supply 6V–12V DC, 1A– 1.5A

7805 5V voltage regulator and heat sink to drop the 12V to 5V for the display’s backlight

Case from vellemanusa.com

Push-button switches ( 2) momentary, normally open Soldering iron and solder

Wiring diagram Download from makezine.com/14/ diyscience_spectrometer or follow the one in this article.

Photograph by Phillip Torrone

134 Make: Volume 14