RC Low-Pass Filter

A resistor and capacitor that pass low frequencies and roll off high ones — the workhorse of signal conditioning: debouncing, anti-aliasing, smoothing a PWM into a voltage, or just cleaning noise off a line.

• R1 — in series with the signal.
• C1 — to ground. At high frequencies the cap looks like a short, so it pulls the fast wiggles down to ground; at low frequencies it looks open and the signal passes.

Exposes: in, out, and gnd.

Cutoff is fc = 1 / (2π·R·C). With 1 kΩ and 100 nF → about 1.6 kHz: content below it passes, content above is attenuated 20 dB/decade. Change R or C to move the corner.