Very basic transistor usage

From: Jason Richard (pcjason*SPAMTHIS*_at_sbcglobal.net)
Date: 10/09/04 

Date: Sat, 09 Oct 2004 22:21:29 GMT

First off, please excuse my ignorance as I know very little about this stuff
and searching google has only helped to confuse me more.
What I would like to accomplish is to drive 12 bi-color LEDs (red/blue) from
two seperate inputs. I would like the red potion of the LEDs to light when
there is network activity and the blue LEDs to light when there is hard
drive activity. This seems simple enough, but the bi-color LED is common
cathode, and judging by the readings I took, the network and hard drive LEDs
toggle the cathode to turn on or off the LEDs. So, what I was thinking is
that I could use a transistor to drive the anodes of the 12 LEDs, but thats
about as far as I got. The specs of the LEDs are Blue: 3.2v at 20mA and
Red: 2.2v at 20mA. Also, the readings I took showed the hard drive activity
LED cathode swinging from 5v (off) to 0v (on) and the network LED swinging
from 3.3v (off) to 0v (on). Any drawing of a suitable circuit would be
greatly appreciated and any explanation of how the circuit works would be
even better!
Thanks for any and all help!
-Jason

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