Algebraic expression

okay, so, I'm not got at all with coding in VB 08 and I need help!
I'm was trying to figure out the amount of "charge" my iPod touch can hold from it's original state.
I used y = Ce^(kt) to model it.

Here it is:

ln(%/100)/(ln(4/5)/400)=c

The variables are % and c

% = the percent of change you are aiming at multiplied by 100 (i.e 50% = .5*100 = 50, so the percent without the percent sign)

c = how many charges it will take to reach that capacity percent

Now with than and simple algebra you can figure out when your battery reach a desired capacity.

How I got the formula:

First, things I assumed:

1. Battery capacity exponentially decreases
2. Battery capacity goes from 100% to 80% in 400 charges



OK, here is the math stuff:

y = Ce^(kt)
or
% = Ce^(kc)

Plug In the info we know

80 = 100e^(kc)
80 = 100e^(k400)
(80/100) = e^(k400)
ln(80/100) = k400
(ln(80/100)/400) = k

again

% = Ce^(kc)

% = 100e^((ln(80/100)/400))c
%/100 = e^((ln(80/100)/400))c
ln(%/100) = ((ln(80/100)/400))c
ln(%/100)/(ln(80/100)/400) = c

80/100 simplifies to 4/5

ln(%/100)/(ln(4/5)/400)=c



SOURCES:

Quote:

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Charge Cycles

A properly maintained iPod battery is designed to retain up to 80% of its original capacity at 400 full charge and discharge cycles.

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http://www.apple.com/batteries/ipods.html



ALL HELP APPRECIATED!!!:eek2:

Quote:

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Originally Posted by Ohfoohy

okay, so, I'm not got at all with coding in VB 08 and I need help!

ALL HELP APPRECIATED!!!:eek2:

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What kind of help? You haven't told us a thing about what you want done. If your looking for some code to do that it's very simple.

Code:

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        Dim Percentage As Decimal
        Dim Charges As Decimal
        Decimal.TryParse(PercentTextBox.Text, Percentage)
        Charges = Math.Log(Percentage / 100) / (Math.Log(4 / 5) / 400)
        chargeLabel.Text = Charges

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Thats it?

How would I display the answer?

Quote:

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Originally Posted by Ohfoohy

How would I display the answer?

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Make a Label named chargeLabel, a TextBox named percentTextBox, and a button named calcButton.

Double click the calcButton in designer mode to view the Click Event and put that code in. The very last part, chargeLabel.Text = Charges, will display the answer inside the chargeLabel.

Just as I suspected! Thanks!

Quote:

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Originally Posted by Ohfoohy

Just as I suspected! Thanks!

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No problem, post if you have any more questions about the program.