Specifications

2.4 Power & I/O Interface

Since one of the overall design requirements of this project is to connect the

portable unit to the base unit for both charging the battery integrated into the

portable unit and data transfer, a means of connecting both units must be

considered. While two separate connections could be used, it would be

inconvenient, would add part count, and would create needless complexity.

Given the fact that this will not require a large amount of high speed data

transfer, nor massive power transfer, a simple, integrated connector should be

used.

There are many options for such a connector, but it would be the most

straightforward to use an existing option that can support both power and data.

Essentially, there must be at least two data transfer lines (receive/transmit), and

two power lines (V+/V-). In addition, this connector must be of a reasonable size,

given the small portable unit. It must also be able to withstand the physical

stresses placed on it, as well as a long life (high number of duty cycles). Of

course, it should also be easy for the user to use, especially in the case that the

user may be intoxicated.

2.4.1 USB

This is a popular, widely-used connection format used in many consumer

electronic devices. It is four pins, and has high availability for both connectors

and cables. In addition, it is proven and reliable to be able to withstand both

stresses and many repeated uses. For this purpose, it is assumed the

microcontroller has native USB. If not, conversion chips would have to be used;

this would increase complexity and cost, as well as add possible points of failure

for debugging the circuit. However, it is also a connection format many

nontechnical people recognize, and one for which replacement cables may be

bought easily at many stores. For this purpose, a female USB Type B connector

(shown in Figure 2.4.1-1) would be used on the portable unit end, while a female

USB Type A connector (shown in Figure 2.4.1-2) would be used on the base unit

end. They would require a cable to be connected together.

However, one aspect that has to be taken into account is the need for a cable.

This is just another piece that must be carried by the user in their vehicle. In

addition, it also creates a cable that must be present in the car’s cabin area,

between units. This could create an inconvenience for the user and possible

safety hazard depending on the mounting point of the base unit.