Specifications

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Enclosure Design
Sketches of our preliminary design concept are provided in Section 3.8, followed
by graphical creation of Breathalyzer unit in the secondary designs utilizing the
well-known Photoshop software.
2.9 Display
It is assumed that the operator of the system may not necessarily be a
“technologically inclined” individual. As such, it is necessary for the design of any
unit requiring a human interface to be clear and concise in its messages to the
operator. This is evident in personal electronic devices across every aspect of
industry, from personal communications devices such as cell phones and
adjustable two-way FM radios, to configurable remote control devices for
operating home theater equipment. In order to facilitate this ease of status
communications with the operator, a digital display is a necessary component of
a successful design. A wide variety of such displays are available, defined by
their capabilities such as displaying custom programmed images, letters and
numbers, backlighting for ease of viewing in low-light scenarios, viewable area
dimensions, methods of communication with the control logic, as well as their
per-unit cost. The requirements for a display on the hand held unit include the
ability to display numeric digits that indicate the detected blood-alcohol content of
the individual under test, as well as a timer indicating the time remaining until a
test can be taken. The display must also be small enough to fit within the size
limits of either enclosure. While it would be advantageous to display text and
images to the user for the purpose of communicating system status or
communication messages, it is not considered a necessity for easy and
successful device operation.
2.9.1 Seven-Segment Display
This style of display is probably the most mature display technology in the field of
digital electronics. A seven-segment display is an electronic display device
capable of rendering images of the set of Arabic numerals 0 to 9, as well as
several letters of the alphabet (varying in case). These types of displays have
been in use for the better part of the last 60 years, and have been crafted from a
number of different lighting techniques, from LED arrays, to ideal arrangements
of incandescent filaments. Typically, they require an individually driven line input
for each segment of the display that is to be powered. A convenient way around
this problem involves the use of a digital multiplexer with a constant current drive
output on each pin. Most seven-segment display manufacturers will suggest a
driving integrated circuit to use with their particular display, but there is nothing
that prevents the designer from individually driving each input to the display.