raatools/

🔌 Elektronikk

Motstandsdekodere, LED-kalkulatorer, kondensatorverktøy og mer for elektronikk-hobbyister

Component maths for people with a breadboard in front of them. These tools cover the calculations you hit repeatedly while building a circuit: what resistor a part needs, what a colour band or SMD marking means, how wide a trace has to be, and how long an RC network takes to settle.

Everything is worked in the open. Each tool shows the formula it used and the numbers it put into it, so you can check the result against your own working rather than trusting a black box — which matters when the consequence of a wrong answer is a dead component.

Which tool do I want?

If you…Use
You have a resistor in hand and need its valueMotstand fargekodedekoder
The part is surface-mount with a 3 or 4 character codeSMD motstandskodedekoder
You are driving an LED and need the series resistorLED-motstandskalkulator
You need to drop a voltage down to a reference levelSpenningsdeler-kalkulator
You are sizing wire for a current, or worried about heatLedertverrsnitt (AWG) referanse
You are laying out a board and need copper widthPCB sporbredde-kalkulator
You are building a timer or oscillator555 Timer-kalkulator
You need a time constant for filtering or debouncingRC tidskonstant-kalkulator

Tolerance is the thing beginners forget

Every calculation here produces an exact number, and no component you can buy is exact. A resistor sold as 220 Ω with a gold band is guaranteed only to sit within 5% of that — anywhere from 209 to 231 Ω. Stack a few 5% parts in one divider and the output can drift further than the reading you were trying to achieve.

This matters most where a result feeds a threshold. A divider setting a comparator trip point, a timing network deciding a pulse width, a current limit sitting just under a part's maximum — in those places, work out what the answer becomes at the tolerance extremes, not just at the nominal value. Where it matters, buy 1% parts; they cost almost nothing more.

The same applies to the standard value the tools round to. E24 gives you 24 values per decade, so the nearest stocked resistor to a calculated 237 Ω is 240 Ω. That is usually fine, and the tools tell you both numbers so you can decide.