First, a little disclaimer:

I’m by no means an expert on this subject. But I do hold a little interest in electronics (and programming. And procrastination. Sometimes I combine those :P).

Btw, It’s been a while since last time I blogged. I probably will edit this post a bit in the following days. Also, I finally made BloGTK 2.0 work in 64-bit Ubuntu 10.04 LTS.

Resistor E-series

(Screenshot from my little test program – Ok I’ll admit I’m no GUI expert :P)

Resistors come in fixed “preferred values” determined by what “E-series” they belong to. Which says how many resistors there are in a decade (1 to 10, 10 to 100, 100 to 1000 etc ohms).

The E series are standardized to have 3, 6, 12, 24, 48, 96 or 192 values pr. decade. E.g. E24 have 24 values. Generally the value is determined by a simple formula:

Ri = 10^(i/Eseries)

Where:

  • Ri = A “preferred value” resistance normalized to 1.00 – 9.99 ohm for the i’th index resistor in a given E series. Multiply or divide by factors of 10 for a given decade.
  • Eseries = is the E-series value: 3, 6, 12, 24, 48, 96 or 192
  • i = is the (zero-based) i’th index, up to Eseries-1 (2, 5, 11, 23 etc).

E.G. The last index in E24 is 23. The first is zero (always).
E series below and including E24 the is rounded to two significant digits.
Above E24 is rounded to three significant digits.

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