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DIY TSA HOW TO Make aSafety spectrometerBy Phillip Torrone November 18th, 2008 2:43 pm Category Arduino, Craft,Electronics, Science

Make a device that identifies dangerous liquids by analyzing light By EricRosenthal

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After air travel security banned bottled water and baby formula, I beganwondering why they didnt use a device to determine the contents ofliquids. If a liquid was detected to be safe, security could allow it on theplane. Spectrometers can identify the chemical makeup of a material byshining light on it and analyzing the precise mix of colors that bounce back.

These devices are usually very expensive, but Ive designed a simple andinexpensive one that can identify liquids. You can also adapt it to determinethe color of a swatch of paper or cloth or to identify a gem or semipreciousstone.

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 debugthe source code. Collecting the liquids and building the database took oneevening, and it was fun!

MATERIALSArduino board from sparkfun.com. Use the Arduino NG or the latest USBversion, the Arduino Diecimila.

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

(IR) phototransistor

-watt resistors: 220 (5), 1K (2), 2.2K, 18K

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

Power supply 6V12V DC, 1A 1.5A

7805 5V voltage regulator and heat sink to drop the 12V to 5V for thedisplays backlight

Case from vellemanusa.com

Push-button switches (2) momentary, normally open

Soldering iron and solder

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

SCHEMATIC DIAGRAM OF SPECTROMETERAn all-controlling Arduino board drives 5 colored LEDs from output pins,along with a serial LCD display. Digital inputs from buttons switch betweenlearn and identify modes, and analog input from the phototransistor isanalyzed to identify the sample. A 7805 voltage regulator powers the LCDbacklight.

A LITTLE SCIENCE BACKGROUNDA spectrometer measures the properties of light over a specific portion ofthe electromagnetic spectrum. Because all materials have a unique spectralsignature, spectroscopic analysis can identify materials from the light thatthey reflect or emit. Mixtures of materials produce combined spectra, and bymeasuring the intensity of light at each wavelength, a spectrometer candetermine the overall chemical makeup of a material under investigation.

When material burns, a spectrometer can detect and analyze the light itemits to determine the materials composition. In astronomy, highlyspecialized spectrometers are used to determine the composition of thegases that are ionizing and emitted as light energy from a star.

HOW ITS DONE1. 1. An Arduino board sequentially illuminates 5 different colored LEDs

(light emitting diodes): blue, green, yellow, red, and infrared.2. 2. As each LEDs light passes through a vial of liquid, we measure the

intensity of the light detected by a phototransistor. See the wiring

diagram above to wire together this part of the spectrometer.3. 3. Our spectrometer has a learn mode and an identify mode. In the

learn mode, a known sample is placed in the unit and sampled at eachwavelength emitted by the LEDs. The sampled values are stored in theArduino memory. In the identify mode, an unknown sample is spectrallyscanned, and the software in the Arduino compares the values of thescan with the values stored in the database.

4. 4. A simple algorithm makes a best guess to identify the liquid, which isthen displayed on a serial LCD. I think youll be impressed by itsaccuracy.

Go online to get the wiring diagram, source code for the Arduino, partslist, and other info at creative-technology.net/MAKE.html.See the spectrometer in action and get a peek under the hood atmakezine.com/14/diyscience_spectrometer.More photos at makezine.com/go/spectrometer.

Eric Rosenthal is president of Creative Technology, LLC (CTech), a companyspecializing in new and advanced imaging technology consulting anddevelopment.

References:

Make: Arduino

Arduino Starter Kit

Getting Started with Arduino

http://creative-technology.net/MAKE.html

http://www.make-digital.com/make/vol14?pg=136

http://makezine.com/14/diyscience_spectrometer

http://makezine.com/go/spectrometer

http://seetron.com

http://sparkfun.com

http://vellemanusa.com

Make 14 -Optics

From MAKE 14 Page 134. To get MAKE, subscribe or purchase singlevolumes.

PHILLIP TORRONE

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