# Is there anything special about the 4.7 value?

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

1. ### riccardo manfrinGuest

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 PittsGuest

Awesome bit of information there. I've often wondered this myself. I
had noticed 33, 47, and 56 frequently. Now I know.

4. ### George HeroldGuest

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.

5. ### Daniel PittsGuest

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

6. ### amdxGuest

Maybe you've been in San Fransisco a little to long?
Mikek

7. ### Jasen BettsGuest

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

10^0
Yes

8. ### amdxGuest

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

Mikek