Specifications

Since most current sensors don‟t have an output that 5V or higher, their voltage will

need to be modified to that accepted by the microcontrollers in the same way as above.

These voltage divider circuits will be included on the same circuit board that the sensor

is mounted to in order to allow for any current sensor to be used in the case that one

fails.

5.6.2 Battery Charge State Sensors

It will be our next task of computing in real time the amount of time remaining that the

battery can be used. This can be done be using the data collected by the

microcontroller in the power usage calculations. The amount of energy remaining in the

battery will also be another consideration for our battery charge state calculations, as

well as the minimum power level that the battery can reach before risking damage to the

battery.

This task will be accomplished using a sensor to monitor the energy level of the battery.

The minimum energy level allowed for the battery will be a set value that is programmed

into our microcontroller. This number will be subtracted from the energy remaining,

giving us the total amount of energy that can be consumed by our components.

Once this task is accomplished, the overall battery charge state will be determined by

dividing the energy available to the components by the power wattage that they are

consuming. This operation will leave us with the time value of energy remaining for the

components. If we are left with a negative value, this means that we are storing more

energy than we are consuming, and time remaining on the battery cannot be calculated.

If left in this condition, the battery will be able to power its components indefinitely.

With the time value of power remaining determined, the microcontroller will be able to

export this information to the LCD screen to be displayed. If we are in fact storing more

energy than we are consuming, then this will instead be referenced on the screen in

place of a time value. This function will be done by the same microcontroller that

performs the power usage calculations.

AS it would be highly undesirable to drain the battery of more power than it could

handle, our group has decided to add an alert system that will warn the user when the

battery is dangerously low on energy. A small speaker will be controlled by the

microcontroller to go off whenever there is less than 5 minutes remaining on the battery.

This will give the user enough time to ensure all data on the laptop is properly saved

before power is cutoff to all external components so the battery is able to recharge itself.

In order to calculate the charge state of the battery, its voltage must be known. This is

the same voltage that was necessary for the power calculations in section 5.6.1, so the

same voltage divider circuit that was already built for those calculations, can again be

used for these calculations. There is a linear relationship between the batteries voltage

and its percentage remaining. At 100% full, the batteries voltage should be 13.1V, and

at 0% its voltage should be 10.5V. In reality, at 10.5V, the battery is not completely

empty, but it is at this point that the power it outputs becomes pretty much useless.