A set of interactive calculators for passive circuits: RC and LR low-pass/high-pass filters, RLC filters, band-pass/band-stop filters, and a capacitor charge/discharge calculator. Each tab computes the missing component or frequency from the others (e.g. cutoff frequency from R and C, or required capacitance from a target cutoff frequency), snaps values to the E12/E24/E96 series, and plots the resulting frequency response or voltage curve.