Capstone: design a filter to a spec

Apply everything: design, simulate and verify a filter that meets a specification.

Your brief: design a first-order RC low-pass filter for a sensor signal. It must pass a 100 Hz signal with less than 1 dB loss and attenuate 10 kHz noise by at least 30 dB. Use E12 resistor values and a ceramic capacitor of 100 nF or larger.

1. Choose fc about 500 Hz and compute R from fc = 1/(2 pi R C) with C = 330 nF.
2. Build the circuit and run .ac dec 100 1 100k.
3. Use cursors to read gain at 100 Hz and 10 kHz.
4. If the spec fails, reconsider: a first-order filter rolls off 20 dB per decade, so check whether 30 dB at 10 kHz is realistic and what you would change (hint: second order).
5. Use .step on R to explore the trade-off and .meas to record gains.
6. Write down your final values and a screenshot of the Bode plot.

Share your result with us through the Contact page; we are happy to review capstone projects.