Education Technology
Free Downloadable Resistor Value Computer

OK, so, it’s not really that hard to learn to read a resistor without a special tool, but ever since I saw the free downloadable nuclear bomb effects computer I have had a soft spot for these circular slide rules. And this one from Rob Ives might make a cool gift for a young maker to get him or her painlessly over the hump. [Thanks, Rob!]

14 thoughts on “Free Downloadable Resistor Value Computer

  1. While you’re on the topic of resistors and sliderules…
    From an old posting on the USENET sci.electronics newsgroup….(edited for relevance)

    From: Dave Slee
    Newsgroups: sci.electronics
    Subject: Re: Sliderules (do they still exist?)
    Date: Wed, 18 Oct 1995 21:52:16 GMT
    Organization: Soil Machine Dynamics Ltd.
    […]
    Take your standard slide rule and doctor the scales. Add some new markings: the standard resistor
    values:

    1, 1.5, 2, 2.2, 3.3, 4.7, 5.6, 6.8, etc. (have I missed a few? so what you get the idea)

    Mark them as little dots on the ratio scales.

    Now a pair of scales on a slide rule work on ratios. If you want a potential divider that has a 3:7
    ratio, put the 3 on one scale against the 7 on the other scale. Now find the pair of dots that come
    closest. These are the standard resistor values that are the best approximation to the required
    ratio. The error in dot spacing gives you some idea of how far you are out.
    [end of quote]

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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