Re: Help Getting Started - Simple DC Circuit

[piggybacking - for some reason Mark's reply didn't
show up here...]

I'm just back from Radio Shack with a package of these to get started
thinking:

http://www.radioshack.com/product/index.jsp?productId=2062588&cp
20 assorted LEDs, 2 - 3V, 10-20 mA

(They were the only thing economical.  Other LEDs were one or two per
package, $1.98 to $4.98.  I'll get another package when I go to get the
battery holder & resistors.)

Am I reading the specs right to use Vcc = 3 V, Vled = 2.5 V and Iled = 15
mA?
R = (3 - 2.5) / 0.015
  = 33.33 Ohms


Since they are assorted LED's, I think you can
count on using 'assorted' values for the resistors.
Try finding a set of resistors from 47 ohm to maybe
150 ohm. Test each LED with the higher value
resistors and step down until a reasonable
brightness is achieved.

When I did electronics many years ago most of the resistors were in the
kiloohm and megaohm range.  33 ohms seems wrong.  Am I missing something?


Nope, because you're dropping such a low voltage
(0.5 volts) at such a low current (.015 A).

A Vled of 2.5v just seems a bit high to me,
though; I'd suggest using 2v in your calcs.
You can always step down to a lower ohms
value if an LED is visibly dim.
.

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