[sdiy] Best 2-pole Sallen Key LPF calculator

[Tom Wiltshire]

Hi All,

What's your favourite 2-pole Sallen Key LPF calculator?

I'm looking for one that gives actual component values rather than 2.31573452nF, like many of the javascript ones do.

I read a very interesting article on the Electronic Design site, which gives many useful simplifications for the equations.

	http://electronicdesign.com/analog/learn-limitations-low-pass-sallen-key-filters

It occurred to me seeing "Simplification 2: Set filter components as ratios and gain as 1" that the obvious ratio n for the capacitors would be the E series (either E6 or E12). So then I started playing with the maths for that, assuming a Butterworth filter (e.g. Q = 2^-0.5 = 0.707). A decent calculator would help me check I'm not going wildly wrong.

Thanks,
Tom