Gordon Henderson wrote:
In article , Dave Baker wrote:
"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?

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?

Missing the "Countdown" music in the background ;-)

It's the way I'd do it - you subtract the biggest and so on, however
the tolerances are cumulative - so if you used 1% resistors, you might
be fine, but lower tolerance resistors and it might be out by too much...

Surely if you used, say, 2% resistors the maximum you could be out in
total is 2% (high if they're all high or low if they're all low). In all
probability some will be high and some low so the total error will be
less than 2%.

Which brings me to the method where you find a nominal value of resistor
(or a couple combined) close to what you want and measure a few until
you find one where the actual value is near enough spot on.

--
Dave