# BestPair II Voltage Divider Resistor Pair Picker Software

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

1. ### TimGuest

Hi,
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
http://www.velotec.com/BestPair.htm

Thanks for looking.

Cheers,
Tim

2. ### Rene TschaggelarGuest

Thanks for having a look at my app doing the

http://www.ibrtses.com/products
http://www.ibrtses.com/products/teiler22.zip

Rene

3. ### Ralph MoweryGuest

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
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. ### GenomeGuest

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

DNA

5. ### Bob MonsenGuest

How about my silly javascript version:

http://home.comcast.net/~rcmonsen/resistors.html

--
Regards,
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. ### John PopelishGuest

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.

8. ### GenomeGuest

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.

Cheers

DNA

9. ### Rich Grise, but drunkGuest

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. ;-)

Cheers!
Rich

10. ### GenomeGuest

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

Anyway

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

Cheers

DNA

11. ### colinGuest

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 =^.^=

12. ### Joseph2kGuest

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.

13. ### Alf KatzGuest

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.

Cheers,
Alf