Re: Help Getting Started - Simple DC Circuit

Randy & David -- Thanks for the replies.

> 2 'C' cells in series should give you enough power
> for short periods, and 3 volts will be sufficient
> to light the LEDs. You could try 2 'AA' cells, but
> I'm guessing they won't handle 30x0.02A = .6A for
> very long (if at all).
>
> Each LED&switch will need a separate resistor.
> Don't try to parallel them thru 1 resistor; you'll
> let the magic smoke out of the LED's. :(
>
> To calculate the resistor values:
>
> R = (Vcc - Vled) / Iled
>
> where Vcc is the supply voltage, Vled is the
> forward voltage drop of the LED, and Iled is the
> operating current of the LED.
>
> You can find a minimum R value for your LED's,
> and try larger values that still give acceptable
> brightness with less power consumption.
>
> HTH

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

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?

Thanks again!

-- Mark


.

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