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Tuesday, 24 July 2012

Linear - Log etc. Potentiometer Conversion


sometimes it's not always possible to get the response you want from an existing potentiometer and sometimes like me, you don't want to have to keep buying loads of different types of potentiometer
or you're just too lazy to reach upto the draw with the log pots in and the linear ones are nearer, whatever the reason you can alter the response curve using the following schematics - I didn't bother doing a stripboard layout for these because it's pretty much 1 or 2 resistors - I tend to use resistors the same value or higher than the pot value however you can bias the curve response to one side or the other using lower values that the pot.

anyway experiment until it does the right thing, that's the best way


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4 comments:

  1. Anonymous6 April 2014 at 02:26

    Are you sure about Log and Rev Log drawings?
    I mean, I always believed that was the opposite way...
    Am I wrong?

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  2. Anonymous6 July 2024 at 16:33

    for example: using a Poti 10k, set to middle (5k + 5k), and a R with 5k;
    normally the poti would give 50% of Vin;
    with R at the lower side (A-C, 1-2): upper is 5k, lower is 5k||5k=2.5k => 2:1 => 33% out (lower than without R) = "banana";
    with R at upper side (B-C, 2-3): upper results in 2.5k, lower is 5k => 1:2 => 66% out (higher than without R) = "hill";
    so, for me it looks like diagram "banana" and "hill" need to be swapped, right?

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  3. Anonymous3 August 2024 at 11:18

    turning a knob clock wise (CW), we expect to increase electrical values like volume or brightness?
    "Logarithmic" is used due to our sensitivity in perception - we are more sensitive to small changes on small levels, but on higher levels to increase the sensation we need a much higher step - for example if we recognize a step of 30% as significant: on a level of 1 that is a rise to 1.3, a absolute (linear) increase of 0.3, later on a level of 10 it would be to 13, so by full 3 units.
    That is, what we call "logarithmic", e.g. for audio, turning the know CW for an angle of 10° (linear) may increase signal voltage by 10% each(!) time (1.00, 1.10, 1.21, 1.33, 1.46, 1.61, 1.77, ... 10.0, 11.0, 12.1, ...) - well, from a mathematical view such a curve is called "exponential"! (resistance R=f(position) will be an exponential function, showing the "banana" curve!
    ... but there might be also local and practical differences. Like with material flow (fluids, water, air), where CCW opens for more and CW closes.

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