PCB Design
Trace Width Calculator: https://www.4pcb.com/trace-width-calculator.html
Handy calculator for figuring out PCB trace widths based on current and temperature requirements.
LC Filter design
LC Filter calculator: https://rf-tools.com/lc-filter/
Enter filter topology, order, input/output impedance, cutoff frequencies, and ripple requirements
Outputs the either the exact or the nearest standard component values needed to implement the filter, along with a schematic of the filter and a bode plot of the frequency response
Switching Power Supply Filter Design app notes: https://www.ti.com/lit/an/snva538/snva538.pdf (edited)
Section on parallel damped filter is a good reference on how to use damping resistors to eliminate resonance from a passive LC filter
Textbooks
https://drive.google.com/file/d/12sun2JBasXaoNDLZOBjQRBu2lIeI1aFa/view?usp=sharing
The textbook for Electronic Design, one of the better texts on electronics fundamentals
https://drive.google.com/file/d/1wlQD3nnpW5N2x0rdbe7Yf297_CyEb_g2/view?usp=sharing
The textbook for Power Electronics, very good intro text for power electronics
https://drive.google.com/file/d/1SNHvNBDIcWseuGaRUFVAuoEPjc1r7Bfm/view?usp=sharing
A fairly comprehensive overview of practically every kind of sensor