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Makezine_COTM_Resistors-BadgeWhat if you need a 10-ohm resistor? No, not 9.92 ohms, but precisely ten? Gareth of Let’s Make Robots shows how simply filing a little bit away from the resistor’s casing increases its resistance. Now, what would you do if the measured value was 10.02 ohms?

John Baichtal

My interests include writing, electronics, RPGs, scifi, hackers & hackerspaces, 3D printing, building sets & toys. @johnbaichtal



  1. Dave says:

    To trim that 10.02k resistor to 10..0k?
    Simple: shunt it with a 5.01Meg resistor!

  2. trkemp says:

    I believe that Gareth ought to seal the resistor back up with a bit of paint or a clear finish like nail polish. I may be misremembering, but I believe that if the carbon film is exposed to the atmosphere, humidity will change the value of the resistor. Also, if you need that kind of precision on a resistor you may need to control the temperature.

    1. I think you are definitely correct. We discussed this when Gareth originally posted this idea on

  3. David says:

    When replacing components in factory assembled circuits, the color code is not always “true” especially for odd but precise values. High precision components are spendy so a manufacturer may buy gobs of cheaper units then measure and high-grade the spot-on units.

  4. Randy says:

    His meter is only accurate to +/- 1% and the resistor was off by less than that when he started so he is wasting his time. This might be useful on a higher tolerance resistors.

    1. I believe that Gareth’s original goal was to get two resistors to match values as closely as possible. This was to form a resistor bridge that would replace a potentiometer when modifying a hobby servo for continuous rotation. This provides feedback to the servo electronics that the servo is positioned exactly on center.
      So the idea is to get two values that match, not necessarily to be less than 1% accurate on the value of 10k itself.
      The original hack, as well as some interesting feedback from other LetsMakeRobots members, can be found at:

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