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Calculating preferred resistor values

Discussion in 'Electronic Basics' started by Rheilly Phoull, Jan 15, 2004.

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  1. G'Day All

    Can anyone help me out with the formula that calculates the various values
    used for the preferred ranges, like say 1% and 5% ??

  2. Do you mean the different value ranges like E12, E24, etc.? These are
    logarithmically spaced, but unfortunately there is no direct formula to
    calculate their exact values.

    For the E12 series the approximate values can be computed using the formula
    10^(n/12), where n goes from 0 to 11. For the general case, the approximate
    values for the range Em are given by 10^(n/m), where n = 0,1,2,...,m-1.

    If you apply this to the E12 series, you'll see that the values you get are
    pretty close to those of the true E12 series, but deviate somewhat in a way
    that is more complex than simply rounding the values.

    This link may be helpful:

    Costas Vlachos Email:
    SPAM-TRAPPED: Please remove "-X-" before replying
  3. Gareth

    Gareth Guest

    I wrote a simple Windows program which finds the nearest preferred
    resistor value from the E12, E24, E48 or E96 series. It uses a look up
    table not a formula.

    Email me if you (or anyone else) want a copy.

  4. Yeah, thanks for the thought.
    I'm just diddlin' about learning C++ and thought I'd re-invent the wheel for
    something meaningful to write.
    My first attempt uses an array with the values in but I was looking for a
    more elegant method.
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