Specifications

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Figure 3.3.1-1: Designed schematic for hand held unit power supply
3.3.2 Control Unit Power Supply
The needs of the control, or base, unit are fairly similar to that of the portable
unit. However, the control unit will be hardwired to the power in the vehicle. A
consideration to be made, however, is how much power is being consumed while
the device is idle. The vehicle’s line to be used is a 12V line; however, this is
from a battery while the vehicle is off. As such, it would be wise to not drain the
vehicle’s battery.
In addition, the condition of the vehicles (and the conditions of their batteries) will
not be consistent in all installations of the overall system. As such, it is imperative
to reduce idle power draw as much as possible. To do this, optimizations will be
made for the control software to reduce or eliminate the draw of certain
components which would not be actively needed during idling.
Otherwise, the system will interface with the constant +12Vdc line in a vehicle’s
electrical system, and regulate this voltage. A schematic of the control unit’s
power supply is available in Figure 3.3.2-1. There will be no charging circuit
since, as mentioned, the power is sourced directly from the vehicle, rather than
adding another battery. Rather, although in the schematic, the charging circuit
will not be populated.
Also, in order to protect against a large transient fluctuation from the power
source, a protection device is inserted near the beginning of the circuit to help
protect the rest of the circuit. While LEDs were considered as an addition to this