RC filter cutoff calculator

electronics

Interactive first-order RC low-pass: cutoff frequency and magnitude response.

A first-order RC low-pass filter has cutoff frequency \(f_c = \dfrac{1}{2\pi R C}\), where the response is \(-3\) dB. Drag the sliders to see how the components set the cutoff.

viewof R = Inputs.range([100, 100000], {value: 10000, step: 100, label: "R (Ω)"})
viewof C_nF = Inputs.range([1, 1000], {value: 100, step: 1, label: "C (nF)"})
fc = 1 / (2 * Math.PI * R * (C_nF * 1e-9))
html`<p style="font-size:1.15rem;margin:.4rem 0 1rem">Cutoff frequency&nbsp; <b>f<sub>c</sub> = ${fc.toLocaleString("en", {maximumFractionDigits: 1})} Hz</b></p>`

Plot.plot({
  width: 660, height: 280,
  marginLeft: 55,
  x: { type: "log", label: "frequency (Hz)", domain: [10, 1e6] },
  y: { label: "|H| (dB)", domain: [-40, 3], grid: true },
  marks: [
    Plot.line(
      d3.range(1, 6.01, 0.02).map(e => 10 ** e).map(f => ({ f, H: 20 * Math.log10(1 / Math.sqrt(1 + (f / fc) ** 2)) })),
      { x: "f", y: "H", stroke: "#0E4D64", strokeWidth: 2 }
    ),
    Plot.ruleX([fc], { stroke: "#6C4AB6", strokeDasharray: "4 3" }),
    Plot.ruleY([-3], { stroke: "#9aa4b2", strokeDasharray: "2 3" })
  ]
})