RC Circuit Calculation

Is there an easy way to calculate an RC circuit if I want a specific voltage in a given time?
As an example: I have 5-volts into an RC and I want it to reach 2 volts in
500ms.
Iw as trying to use percentages and then resorted to a diff eq but that solves for current over time.
TIA
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Never mind, I found my equation:
V = V0 ( 1 - e ^ (-t/RC) )
Thanks anyway
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Having the expression for current, you can note that the voltage across the capacitor is 5-i*R and you can do the rest. If you haven't the solution of the differential equation try
http://en.wikipedia.org/wiki/Resistance-capacitance
under the section called "time domain considerations"
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Don Kelly snipped-for-privacy@shawcross.ca
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