In article , Dave Plowman (News)
writes
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)

The general rule for parallel friggery being:
Start with the standard value above the desired value and add a parallel
resistor from around a decade (x10) up, 56000 gives 5091, 68000 gives
5174 and as DaveP says, 82000 gives the closest at 5242.
--
fred
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