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Is there anything special about the 4.7 value?

Discussion in 'Electronic Basics' started by riccardo manfrin, Oct 26, 2013.

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  1. I see it recurring in every circuit around (especially the 4K7 Ohm resistances).
    Is there some reason behind that (I've read around that it is considered a safe series resistance for leds.. but I've seen it used not just for that)..

    RM
     
  2. Daniel Pitts

    Daniel Pitts Guest

    Awesome bit of information there. I've often wondered this myself. I
    had noticed 33, 47, and 56 frequently. Now I know.
     
  3. I've always thought of this as equal divisions on a log scale. So if there are 6 divisions, and if the first point is is one, the inverse log of zero
    log ^-1(0) =1 (is that how you write an inverse log???) then the next is log^-1(1/6) = 1.467... and then log^-1(2/6) = 2.15... etc.

    Now where the 6/12/24 divisions of the log scale came from I have no idea?
    Was this picked to match 20% and 10% tolerances?

    George H.
     
  4. Daniel Pitts

    Daniel Pitts Guest

    According to the Wikipedia article, you're pretty much exactly right on
    that last bit.

    Take "E6" for example:
    10 15 22 33 47 68

    10*1.20 = 12.0 15*0.80 = 12.0
    15*1.20 = 18.0 22*0.80 = 17.6
    22*1.20 = 26.4 33*0.80 = 26.4
    33*1.20 = 39.6 47*0.80 = 37.6
    47*1.20 = 56.4 68*0.80 = 54.4
    68*1.20 = 81.6 100*0.80 = 80.0
     
  5. amdx

    amdx Guest

    Maybe you've been in San Fransisco a little to long?
    Mikek :)
     
  6. Jasen Betts

    Jasen Betts Guest

    Inverse of y=log(x) is x=pow(10,y).

    10^0
    Yes
     
  7. amdx

    amdx Guest

    ah right, ah right, the color code is pretty!

    Mikek :)
     
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