22.3 The SPETTROGRAFO System
Our innovative device SPETTROGRAFO is a system implementing the simplicity of
use of the existing commercial proposals and the feasibility of the analysis algorithms with new functionalities, missing in the analyzed devices, as the one to use
grating with different pitches or to use colored filters to study selective absorption of
light, or to have the possibility to dim the intensity of excessively luminous sources.
Those little improvements allow the user to gain a better control of the measuring
process, maintaining a good accuracy in the measured quantities using a low-cost
instrument. The preliminary design of the prototype has been described in
Buongiorno et al. (2018); here we report the final version of the system and relative
specific technical characteristics with examples of employment in physics education.
22.3.1 The Hardware Components
In the SPETTROGRAFO system, a webcam is placed inside an aluminum case
mounted on an adjustable tripod (Fig. 22.4). Technical data are shown in Table 22.1.
The dispersive element, a transmission diffraction grating could be placed in front
of the lens of the webcam pointing towards the source whose light has to be
analyzed. Light sources need to have small dimensions in order to produce spectra
with enough separation between adjacent colors (we remind that a spectrum is the
reproduction of the shape of the source at different angular positions with different
colors). The device can be used also with extended light sources, making use of an
external couple of black panels, working as a diaphragm with adjustable width.
Gratings with pitches of 1000 and 500 lines/mm can be used, both allowing
spectral analysis in a range between 380 and 700 nm. The 1000 lines/mm grating
allows to see only the first diffraction order with a resolution of 1.3 nm/pix, while
with the 500 lines/mm the second order is visible, but the resolution decreases to
2.6 nm/pix. A couple of Polaroid filters can be inserted in front of the webcam to dim
the light intensity of the source, avoiding the saturation of the sensor, in case it was
too high. Colored filters can be also inserted in front of the webcam to study selective
chromatic absorption (Fig. 22.3). The light passes through the grating and the
diffraction pattern is registered on the CCD. A USB connection allows to send the
digital image to the PC. A specifically designed ad-hoc software computes and
analyzes the digital information.
Table 22.1 Technical data of
SPETTROGRAFO system
Hardware part
Data
Webcam
Focus: 15 cm—infinity
60 frame per second
Field of view is 60
CCD
640 Â 480 pix 1.2 Mpix
Case
6 cm  6 cm  6 cm
22 SPETTROGRAFO: A Digital Spectrometer for Educational Lab Activities
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Our innovative device SPETTROGRAFO is a system implementing the simplicity of
use of the existing commercial proposals and the feasibility of the analysis algorithms with new functionalities, missing in the analyzed devices, as the one to use
grating with different pitches or to use colored filters to study selective absorption of
light, or to have the possibility to dim the intensity of excessively luminous sources.
Those little improvements allow the user to gain a better control of the measuring
process, maintaining a good accuracy in the measured quantities using a low-cost
instrument. The preliminary design of the prototype has been described in
Buongiorno et al. (2018); here we report the final version of the system and relative
specific technical characteristics with examples of employment in physics education.
22.3.1 The Hardware Components
In the SPETTROGRAFO system, a webcam is placed inside an aluminum case
mounted on an adjustable tripod (Fig. 22.4). Technical data are shown in Table 22.1.
The dispersive element, a transmission diffraction grating could be placed in front
of the lens of the webcam pointing towards the source whose light has to be
analyzed. Light sources need to have small dimensions in order to produce spectra
with enough separation between adjacent colors (we remind that a spectrum is the
reproduction of the shape of the source at different angular positions with different
colors). The device can be used also with extended light sources, making use of an
external couple of black panels, working as a diaphragm with adjustable width.
Gratings with pitches of 1000 and 500 lines/mm can be used, both allowing
spectral analysis in a range between 380 and 700 nm. The 1000 lines/mm grating
allows to see only the first diffraction order with a resolution of 1.3 nm/pix, while
with the 500 lines/mm the second order is visible, but the resolution decreases to
2.6 nm/pix. A couple of Polaroid filters can be inserted in front of the webcam to dim
the light intensity of the source, avoiding the saturation of the sensor, in case it was
too high. Colored filters can be also inserted in front of the webcam to study selective
chromatic absorption (Fig. 22.3). The light passes through the grating and the
diffraction pattern is registered on the CCD. A USB connection allows to send the
digital image to the PC. A specifically designed ad-hoc software computes and
analyzes the digital information.
Table 22.1 Technical data of
SPETTROGRAFO system
Hardware part
Data
Webcam
Focus: 15 cm—infinity
60 frame per second
Field of view is 60
CCD
640 Â 480 pix 1.2 Mpix
Case
6 cm  6 cm  6 cm
22 SPETTROGRAFO: A Digital Spectrometer for Educational Lab Activities
275