The processor may also monitor the battery temperature and remaining battery capacity. The processor uses this information to determine how much power is available from the battery. Under ideal power and temperature conditions the heater can be run at maximum power speeding up the defogging process. But, when the battery temperature and or battery capacity levels are low, the control circuits can decrease the power applied to the heater element, providing some level of defogging capability without causing the system to power down due to low voltage.
Referring to FIG. 8, the example mobile device 100 incorporates a sensor 119 which may be a temperature sensor such as an IR temperature sensor that directly measures the temperature of the window 102 (FIG. 1) or the temperature of the passive optics 105 and/or transparent window 106 or any other component that may be subject to fogging or frosting. The temperature of, for example, the window 102 can be monitored over time and when a large enough temperature change over a short time period occurs such that the window 102 is subject to fogging or frosting, the heater 144 can be activated. When the condition in which the fogging or frosting is likely to occur has passed, the heater can be deactivated. The charge state and other measurements associated with the battery may be obtained from a battery monitoring circuit 202 so as to establish other conditions governing use of the heater. Such battery monitoring circuits are commercially available and are often referred to as a “battery fuel gauge” or the like and are commonly integrated into battery packs to provide information about the battery. The battery monitoring circuit will be discussed in greater detail later.
