Specifications

A basic arrangement of signal flow into the microcontroller and out of the

microcontroller must be established. As such, the microcontroller will obviously

act as the central component in our circuit, ultimately performing all control

functions on board. An arrangement summary is demonstrated in Figure 3.1-1.

Figure 3.1-1: An arrangement summary of signal flow in the portable unit. Small

arrows indicate flow into the microcontroller, and large arrows indicate output

from the microcontroller.

Of course, the overall project consists of two units. In addition to the portable unit

diagrammed above, the control unit performs one of the primary functions of this

device – the interlocking and overall control functionality. Given its semi-

permanent mount inside the vehicle, space requirements are somewhat relaxed,

but are still present. Nonetheless, it must still adhere to the same requirements

detailed above. However, hardware wise, it needs to accept, control, and output

a different set of variables than the portable unit. A high level design summary of

this arrangement is available in Figure 3.1-2.

Power is also a significant consideration, especially in the portable unit where the

power source must be portable. As such, the power solution will also need to be

designed to support all components, as far as voltage and current requirements.

In addition, charging and any power transient considerations will also need to be

made. While the ability for the portable device to operate both directly from

external power and from the internal battery was considered, it was also realized

that the case of the user actively using the device while it is plugged in is not as

likely as the user using the device while exclusively on the battery. As such, the

portable device will always be powered from the internal rechargeable battery.