23 Oct
2011
23 Oct
'11
3:04 p.m.
On 23 Oct 2011 at 20:20, Tony Duell wrote:
Unfortuantely _yes_ !. These are the sort of people
who say 'There are
no 382.73 ohm resistors in the box, and I can't find them in any
catalogue'. When you ask what they want them for, it turns out that's
the value they calcuated using (V_supply - V_f)/I_Led using data sheet
typical values of V_f (LED forward voltate) and I_Led (LED current)
for the nominal supply voltaget hey're using. And they don't believe
you when you tell them to stick in the first 390 Ohm resistor they
find.
A side phenomenon is that few engineering students understand much
about how things are manufactured. If you purchase a reel of 470 ohm
1/4W 10% carbon comp resistors, you may reasonably expect that not a
single one of them will be within 1% of 470 ohms.
(Film resistors are a different matter, however).
--Chuck