On Tue, 08 Sep 2009 18:54:11 +0100, Dave Plowman (News) wrote:
In article ,
pete wrote:
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

Have you Googled for one? 'resistor calculator prog' seems to give plenty
hits.

The one I use - on this Acorn - gives 82k and 5k6 in parallel at a 0.15%
error. With just two in series the best it can achieve is 0.95% (1k3 and
3k9)

Yes, there are lots of downloadable ones (that I presume do what I want).
However I'm looking for an online utility - one where I can go to a web
page that asks:
what value do you want to find?
what family of values (E12, E24 ...) to use?
how close do you want to be

and then it tells you that for a value of X, you need an A and a B in
parallel and a C in series - or whatever the answer might be. The ones
that google spits back merely calculate the result from values you
type in.
I've (easily) got this solution, but I'm looking for a more general
solution in the future. Although, in practice the answer is to
choose the next lowest value and add a preset (multi-turn for extra
accuracy) and tune for maximum smoke.