Specifications

user in a message on the screen. It will also light a LED, which will tell the user without

looking at the display if it is using power or storing power.

For example if the system is consuming power it will display a negative value on the

screen which will light up a red LED that will indicate power usage. This information will

have to be fed to the time calculation as well to calculate the amount of time remaining.

The next possible situation is if the system is storing more power than using. This will be

indicated as a positive number and will also light a green LED such that the user can

see that he is storing power. For example if the system is producing 10 watts and using

5 watts the difference will be shown as a positive 5 watts as well as a green LED. The

time calculation can be infinite if the user is storing energy so we will not display a time

until empty because it is storing energy. The user will instead have a message of no

stored energy is being used.

4.2.2 Battery Charge State Calculations

The battery level will be displayed on the screen as time until empty. Using the power

calculation previously described in the earlier section will determine if the system is

using or storing power. The easy case is that it is storing power and we will just display

that the system is storing power and there is no estimated time for depletion of the

battery. The other case is that if the system is using power we will need some way of

calculating the time remaining. The easiest way we determined is by using the max

voltage across the terminals the battery can have and then comparing that with the

minimal value of the battery and the amount of change between drops in charge as a

function if time. We will be able to calculate the amount of battery time remaining. All

batteries have a cutoff voltage in which usage beyond this value will cause damage the

battery. We will have to inform the user that the battery cannot function any longer and

the system needs to be shut down. We will signal a audible tone when such an event is

going to occur. This will be done by a small speaker that will be mounted on the inside

of the case as in the figure below:

Figure 33 - Low Power Speaker for audible tones

Permission Pending

We may also use this speaker in other aspects of the project, which include fault codes

and heat thresholds. Reaching to all the senses of a user is important when critical