Every now and then situation arises where you need to construct simple filter circuits. Usually a low pass circuit is the most often needed one. A low-pass filter is a filter that passes signals with a frequency lower than a certain cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. Low-pass filters exist in many different forms. Low-pass filters exist in many different forms. One of the simplest electronic low pass filter is RC low pass filter – a first-order filter that reduces the signal amplitude by half (6 dB), every time the frequency doubles (goes up one octave). One simple low-pass filter circuit consists of a resistor in series with a load, and a capacitor in parallel with the load.
The cutoff frequency (in hertz), is determined by the time constant:
Online RC Lowpass filter Calculator page shows a low-pass filter made from a RC section and gives calculator to calculate component values for it. Learning Electronics Low Pass Filter Calculator is also worth to check out.
RC Low-pass Filter Design Tool page is a web application that design a RC low-pass filter. Use this utility to calculate the Transfer Function for filters at a given frequency or values of R and C. The response of the filter is displayed on graphs, showing Bode diagram, Nyquist diagram, Impulse response and Step response.
If you want to design other filters, go to Filter Design and Analysis web page. This page is the index of web calculator that design and analysis analog filters. It is a pretty complete collection having pretty much everything you might need on analog filter design: RC, LC, low pass, high pass, band-pass, notch, active filters, etc.