Product Requirements Document
Cellphone spectrophotometer
Customer:
Engineers:
Advisor committee:
Per A
Elie Glik, Carol Xu
Tom Brown, Jim Zavislan
Contents
Vision............................................................................................................................................................. 2
Environment ................................................................................................................................................. 2
Regulations and Risk Factors ........................................................................................................................ 2
Product Requirement Document .................................................................................................................. 3
Vision
A self-powered spectrophotometer attachment to a modern day smartphone camera to allow spectral
response data for lab and commercial purposes. This attachment should be robust, light, and have a
small profile relative to the cellphone. Simple processing will be done onboard, and expert of the
spectral photo will be possible. Students in small limited budget labs may use this device along with
their smartphone to identify light sources, measure chemical concentrations, compare solutions, and
other metrics commonly done with commercial spectrophotometers. Further vision is a more versatile
low end spectrophotometer replacement. This device will carefully weigh price, profile size, and
resolution in order to accommodate said vision.
Environment
Temperature:
55-90°F – Safe Operation
60-85°F – Meets Operation
Humidity
Under 80% humidity
Note that environment factors have not been tested
During normal operation, no maintenance will be required. Maintenance such as cleaning the glass
surface may be required, depending on use, once a month. Calibration will be required frequently for
higher accuracy.
Device will be less than half the size of a standard tissue box.
Regulations and Risk Factors
No laser is used. LED illumination is not subject to FCC standards.
The system will be designed to mitigate physical risk of the operator even if dropped.
The system will need to be tested under appropriate standards depending on where it is sold. Primary
market will be US until notified otherwise.
Users will require relatively no training under normal circumstances assuming they already are familiar
with their smartphone.
System will require appropriate disposal under regulations in region of use. System will be Rohs
compliant.
Product Requirement Document
The following describes the requirement for the product.
The most important aspect is to stay within the price range for manufacturing the product. The
maximum costs are outlined below:
Manufacturing cost
Estimated sale price
Prototype Budget
$100
$200
$400
The second most important trait is resolvability, resolution, and accuracy of the device. The device
needs to be able to resolve the Sodium d-line which is at 588.9950 & 589.5924nm. The device also
needs to be capable of searching through the total visible spectrum but does NOT need to keep such
high accuracy over the general scan.
The third most important factor is size and weight. The profile should be ideally smaller than the
cellphone and able to either attach to the phone, or be integrated with a cellphone case.
The forth factor is the versatility of cellphone models it is capable of working with. The system needs to
be one unit, but switchable components are acceptable. Thus, some initialization work may be required
by the operator.
Other important factors:
 Onboard computation via an “App”
 Durability: should be able to withstand a 2ft drop without the phone onto an optical table
without breaking
 Should be compatible with the latest version of the Apple iPhone, and the SII Samsung Galaxy
Calibration will be required, and some calibration paper or commonly available light source will be
provided or used. Calibration will be built into the app. It will correct for the baseline by a computational
method. HDR (High Dynamic Range) software may be used to boost the baseline correction, and
increase the dynamic range, optically.
The illumination source can be a standalone, battery powered LED that is included in the device, or may
use the integrated light in the smartphone. The benefit of a standalone option is the amount of light and
direction will be controlled by said device, and the versatility between phones will be increased. The
downside is the added complexity (physical and interface), space requirements, and synchronization.
These factors will need to be taken into consideration.
In order to achieve the resolution requirement of the d-line doublet, as well as obtain a scanning field
over the visible range sensible to smartphone cameras, (a chosen range from 405 to 675nm), a few
options will be considered. These include: a switchable component such as a grating, adjustment to the
device or a multi-layer approach with multiple diffraction gratings. This is predicted to drive up cost,
and make manufacturing more complicated. Therefore, attempts will be made to achieve this resolution
in one go, and reduce system complexity.
The following table summarizes some requirements:
Abbreviation Term
Comparable Value
FOV
Field of View
iPhone: 30mm
NA
Numerical Aperture
iPhone: F2.4
Res
Camera Resolution
iPhone: 8 MP
SystemTime
Volt
Accuracy
Contrast
Weight
Size
Max time for system to
output results
Internal Operating
Voltage
Accuracy of one scan
Minimum contrast
between signal and
noise
Weight of system
Physical Size
Value
1.5µ size
pixels.
3264x2448 =
8MP
10 seconds
Cellphone charging voltage
5V
d-line doublet
?
.5nm
1:2
Max ¾ weight of cellphone
Half the size of a tissue box