In message , Dave Baker
writes

"pete" wrote in message
...
Does anyone know of an online utility that can calculate
what combination of series and parallel resistors are needed
to get a particular value?
Specifically, I'm trying to calculate the best way to get
close to 5250 Ohm, using E12 preferred values. Power consumption
is not an issue and I'd like the value to be +/- 2% as that's
the resistor tolerance.

I'm not looking for the answer, I'm looking for the way to
find the answer. There are lots of websites where you can
tap in resistor values and have it calculate the result, but
that gets long winded. I've got a combination that gives
5253R with 4 resistors, but I'd like to do better

I'm puzzled. Knowing nothing about electrickery I've Googled resistors,
found out what E12 means, got a table of what values are possible which
appear to be 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 and so on in
further powers of ten.

So what's wrong with the following four in series, 4700 + 470 + 68 +12 =
5250 or am I missing something obvious?

Well, 2% of 4700 is 94, which puts both 68 and 12 'within the noise' of
the 4700 resistor. The preferred way to do it used to be to use a number
of similar, but different, values of resistor to make up the value,
hoping that the tolerances of the different batches would even out in
opposite directions. I remember writing a program for the BBC computer
to do this, that gave recommended serial and parallel combinations.

--
bof at bof dot me dot uk