Guides
The reasoning behind the calculators — what the numbers mean, which assumptions they rest on, and where they stop being reliable.
A calculator answers a question you already know how to ask. These guides cover the part before that: why a trace overheats, what a decibel actually measures, why a fence needs one more post than it has sections, why two tools can give different answers and both be right. Each one leads into the calculators it relates to, so you can read the thinking and then do the arithmetic.
Electronics
- How to size a PCB traceHow much current a copper trace can really carry, where the IPC-2221 curves come from, and the three things they do not know about your board.
- Choosing a resistor for an LEDWhy an LED needs a resistor at all, how to pick the value, what power rating it needs, and why wiring LEDs in parallel off one resistor goes wrong.
- Measuring temperature with thermocouplesWhy a thermocouple never measures one temperature, what cold-junction compensation is actually doing, how to choose a type, and where the error really comes from.
- Reading resistor and capacitor markingsColour bands, three-digit codes, the R and V conventions, and tolerance letters — how to read what is actually printed on a part.
- Understanding decibelsWhy decibels use logarithms, when it is 10·log and when 20·log, what 3 dB really means, and the difference between dB, dBm and dBV.
IoT
- Making a battery last a yearWhy sleep current decides battery life, why rated capacity is optimistic, and how to design a duty cycle that survives contact with a real cell.
- Planning a radio link that worksPath loss, link budget and margin — how to tell before you deploy whether a wireless link will hold, and which lever to pull when it will not.
Radio
- Antenna gain and radiation patternsWhat gain actually measures, why an antenna cannot amplify, the difference between dBi and dBd, and how to read a radiation pattern.
- Antenna types, and how to choose oneDipoles, monopoles, PCB inverted-F, chip, patch, Yagi and helical — what each is good for, what it costs you, and the trade nobody escapes.
- Impedance matching and SWRWhy 50 ohms, what SWR and return loss actually tell you, how much power a mismatch really costs, and why a low SWR is not proof of a good antenna.
Finance
- Simple and compound interest, and why the gap growsWhat actually differs between the two, why a quoted rate can mean several things, and what interest calculations routinely leave out.
Home & DIY
- Estimating materials without running shortWaste factors, why you always round up, why a roof is bigger than the house, and the arithmetic that decides bags versus bulk.
Converters
- Working across metric and imperial without mistakesWhich conversions are exact and which are not, why a temperature difference converts differently from a temperature, and where units quietly go wrong.
Reference
- Why two calculators give different answersDifferent conventions, different standards, rounding, and genuine error — how to work out which result to trust when two tools disagree.
How these are written
Everything here is written by Arthur Kingsfield, an electronics engineer working in PCB design and embedded systems — which is why the electronics and IoT guides go into more depth than the rest. Where a guide covers ground outside that, it sticks to arithmetic and published standards and says which it is following.
The guides name their assumptions on purpose. A figure that is exact by definition is described as exact; a rule of thumb is described as a rule of thumb; a published standard is named so you can go and read it. That is the same principle as the calculators themselves, where the formulas arechecked when the site is built rather than taken on trust.