Specifications

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The battery will have to supply power a few main components: the general logic
on the board, and any power required by the alcohol sensor, as well as any other
components such as displays and LEDs. Several battery types will be
researched for their advantages and disadvantages in order to achieve this
purpose. In particular, their sizes will also be taken into account as space will be
a consideration within the portable housing.
Requirements:
Since the portable unit will depend on the battery for operation, it is essential to
ensure that the battery selected will be an appropriate one given the
requirements the portable unit and its user will place on the battery. Due to the
presence of both 3Vdc and 5Vdc lines, the battery must be able to supply both of
these lines. Since voltage regulators generally prefer at least 1.5Vdc above their
regulated output voltages, the required range for the battery to output should be
at least 6.5Vdc. Due to thermal constraints on the regulators, it should also not
be too high. Since 12Vdc is a possible input to both units for other reasons, a
12.5Vdc upper limit is reasonable. Thus, the battery should be able to supply an
output voltage somewhere in the range of 6.5Vdc – 12Vdc.
Again, cost becomes a concern. The battery is a major component, and so, will
have a higher budget. As such, a reasonable limit must be established. Indeed,
due to the high importance the battery has to the circuit as a whole, a limit of
about $50 would be desirable. The fact that the battery will eventually need to be
replaced should also be taken into account. Purchased in bulk, the battery, and
thus maintenance, cost of this unit should not be prohibitive.
The other considerations are those of practicality during use. Given the possibly
intoxicated nature of the end user, safety is a consideration. The battery must be
proven to be stable and not significantly vulnerable to injuring its user if
mishandling or misused. In addition, it must be as compact in size as possible. A
battery can easily overwhelm and greatly increase the size of the portable unit.
Also, as a result, it could also greatly increase the weight of the portable unit,
which is not desirable. Lastly, it must be able to last a decent amount of time.
However, since the battery is rechargeable, a very high capacity battery may not
be needed. Nonetheless, it should last as long as possible.
2.11.1 Alkaline Battery
There are two options within alkaline batteries. There are single-use alkaline
batteries, as well as rechargeable alkaline batteries. The former is popular in the
consumer electronics markets, while the latter is not generally used due to its
very poor performance compared to other types of rechargeable cells. In
addition, the performance of such batteries is poor in high-drain electronics.