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BestPair II Voltage Divider Resistor Pair Picker Software

Discussion in 'Electronic Basics' started by Tim, Jan 27, 2006.

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  1. Tim

    Tim Guest

    There are 480,000 different combinations of standard 1% resistor values. If
    you need 2.75 volts from a 5.00 volt reference, which of those 480,000 pairs
    will give you the closest result?

    For this example there are 9 resistor pairs that will get you to within
    0.5%, but one resistor pair will get you within 0.15%. Only 1 out of 480,000
    combinations is the best pair!!

    BestPair has been upgraded to Best Pair II. If you are interested you can
    get it with instant download delivery here -->

    Thanks for looking.

  2. Thanks for having a look at my app doing the
    same for free :

  3. Ralph Mowery

    Ralph Mowery Guest

    There are several problems with this.

    1. YOu can not be sure of getting .5 % or less error if you have 2 of the 1
    % resistors to start with.
    2. You did not list the resistance of the source and load. If the source
    will not supply the needed current for low values, they are out. If you
    have a low resistance load , the resistors will have to be on the low end of
    the standard values.
  4. Genome

    Genome Guest

    I'd like to know what a 2K74 or a 976R resistor is?

    I noticed this stuff appearing on application notes a while back, what's it
    all about?

  5. Bob Monsen

    Bob Monsen Guest

    How about my silly javascript version:

    No download required at all...

    Bob Monsen

    "I cannot persuade myself that a beneficent and omnipotent God would
    have designedly created parasitic wasps with the express intention of
    their feeding within the living bodies of Caterpillars"
    -- Charles Darwin
  6. To get rid of fly speck periods in parts values, they use the
    multiplier (K, M) to represent the decimal point. If the multiplier
    is 1, they use R.
  7. Genome

    Genome Guest

    Yus.... I wasn't really on about that but I think it is a monster brilliant
    way of doing things.

    I was on about the idea of a 2K74 or 976R resistor versus 2K7 and 1K. Like
    the numbers imply 0%1 (snicker) resistors what no-one is going to specify in
    a design but they appear in application notes in places where no-one would
    specify them.


  8. I think there are a couple of reasons for the three-digit value. One, in
    a 1% resistor, you have to have the next value within 1%, right? (or 2, or
    0.5, or whatever - that's not the point). As for why such a tight
    tolerance, there are probably real engineers who do take resistor values
    into consideration when they're designing something, but, you know, now
    that I think about it, maybe it's an evolutionary thing. Maybe the
    resistor manufacturers' process started turning out batches that were so
    close to each other, so reliably, that they found they could characterize
    a whole batch within 1%, and then they started dicking around with their
    process, and found that they could reliably make a batch of _any value
    they want in the world_ to better than 1% tolerance, so all of the
    resistor manufacturers had a powwow, and said, "OK, so what values should
    we assign?" And they came up with that familiar 1% table.

    Why design engineers use them, well, I could only speculate, other than
    that the value might make a difference, and when they're cheaper than
    carbon, they're the logical choice, so you just pick something. ;-)

  9. Genome

    Genome Guest

    You am obvo'ously drunk coz you did not notice the 0%1 reference.


    I now have my webserver in the attic up and running wiv Slackware and Apache
    so I have to say thank you for the whatever.

    It is..... nice.

    Now I have to figure out how to ask a question in SED about slowing fans
    down so's I can get some sleep, because I sleep in the attic.

    Obsly I need a gmail account and have to do it through google grupes but I
    don't know how to word my request such that JT will desine one for me.

    My anti-spam MAF-ID is lorycfn w389065n- 5- C6M35FQG7NMBW


  10. colin

    colin Guest

    Cool, but I often find I havnt got a full set of resistors and so if I want
    to make a divider thats more exact than i can make with any 2 of the ones I
    have I have to fiddle about trying to work out what set of 3 resistors that
    I do have in series/parallel whatever combination will give the best result.

    (I realy must get some 9k resistors, I so often want to make a 10x non
    inverting op amp gain stage)

    Colin =^.^=
  11. Joseph2k

    Joseph2k Guest

    Along about 20 years ago several resister manufacturers were able to produce
    1% resisters cheaply and the 1% standard values were already set. The
    military and instrument manufacturers were already pushing for 0.1%
    devices. Small wonder that 1% and 0.1% parts are available cheaply now,
    all the patents have run out.
  12. Alf Katz

    Alf Katz Guest

    2K74 is a standard value for 2% tolerance or better resistors (EIA preferred
    value for the E48 or higher range) 976R is a standard value for 1% or better
    resistors (EIA 96 or higher range). These values were derived by choosing
    a set of values whereby the bands of resistance given by the nominal value
    +/- the tolerances just overlap, giving 6, 12, 24, 48, 96, or 192 values per
    decade (e.g. between 100 Ohms and 1K) for E6, E12, E24, E48, E96 and E192
    ranges respectively. E96 is pretty common now as it makes sense for 1%
    resistors. E192 is used for tighter than 1% tolerances.

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