Engineering tools
Electronics tools
Calculators for the small decisions in circuit design: LED series resistors, standard component values and power ratings, with the reasoning and the data behind each one.
Tools we reach for while designing and prototyping hardware. Each one states its formula, picks real standard component values rather than ideal ones, and says what it does not account for.
Standard values, not ideal ones
A formula gives 500 Ω; a parts drawer gives 470 Ω or 510 Ω. The tools here finish the job by choosing a value from the E-series you actually stock, recalculating with that value, and checking the power rating, because a resistor that is electrically right but thermally marginal is the commonest small mistake on a prototype.