Time constant τ, charging times, filter cutoff frequency & live simulation
τ = R × C (seconds)
fc = 1 / (2π × τ) (cutoff frequency)
Vc(t) = Vs × (1 − e−t/τ) for charging
Vc(t) = V₀ × e−t/τ for discharging
At t = τ: ~63.2% charged. At t = 5τ: ~99.3% (fully charged).