+ 5
1k
+ 5
1k
Red Blk
220
IR
Red
Orange
Yellow
Blue
+ 12
7805
2.2k
+ 5
+ 12
USB
AREF
GND
321098 76543210
1111
Digital
TX
RX
PWM2
PWM0
PWM1
Arduino
S1
PWR
1
Data In Backlight power
Crystalfontz 20x4 Serial
Graphics LCD display
SV1
1
Q1
+5V DC
ICSP
D1
IC1
18k
X1
POWER Analog in
5VGnd9V 012345
Phototransistor
PORTABLE SPECTROMETER
+ 12
SCHEMATIC DIAGRAM OF SPECTROMETER: An all-controlling Arduino board drives 5 colored LEDs from
output pins, along with a serial LCD display. Digital
inputs from buttons switch between “learn” and
“identify” modes, and analog input from the phototransistor is analyzed to identify the sample. A 7805
voltage regulator powers the LCD backlight.
A Little Science Background
A spectrometer measures the properties of light over
a specific portion of the electromagnetic spectrum.
Because all materials have a unique spectral signature, spectroscopic analysis can identify materials
from the light that they reflect or emit. Mixtures
of materials produce combined spectra, and by
measuring the intensity of light at each wavelength,
a spectrometer can determine the overall chemical
makeup of a material under investigation.
When material burns, a spectrometer can
detect and analyze the light it emits to determine
the material’s composition. In astronomy, highly
specialized spectrometers are used to determine
the composition of the gases that are ionizing and
emitted as light energy from a star.
How It’s Done
1. An Arduino board sequentially illuminates 5
different colored LEDs (light emitting diodes):
blue, green, yellow, red, and infrared.
2. As each LED’s 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. 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 each wavelength emitted by the LEDs. The sampled values are
stored in the Arduino memory. In the identify mode,
an unknown sample is spectrally scanned, and the
software in the Arduino compares the values of the
scan with the values stored in the database.
4. A simple algorithm makes a best guess to identify
the liquid, which is then displayed on a serial LCD.
I think you’ll be impressed by its accuracy.
Go online to get the wiring diagram, source
code for the Arduino, parts list, and other info at
creative-technology.net/MAKE.html.
See the spectrometer in action and get a peek
under the hood at makezine.com/14/diyscience_
spectrometer.
More photos at makezine.com/go/spectrometer.
Eric Rosenthal is president of Creative Technology, LLC
(CTech), a company specializing in new and advanced
imaging technology consulting and development.
Make: 135
