On 5/19/2010 7:31 AM, scott wrote:

> Why is that weird? The LED doesn't care which leg is connected to the
> logic output pin, it's just a voltage. You could even connect the LED
> between two output pins*, then it would only turn on when one was high
> and the other was low.


There's even a name for that trick: Charlieplexing.

The 3 state had to be simulated by switched, but here's a circuit for 
the Falstad simulator (http://www.falstad.com/circuit/):

$ 1 5.0E-6 10.20027730826997 50 5.0 50
L 224 176 176 176 0 1 false 5.0 0.0
L 224 224 176 224 0 1 false 5.0 0.0
162 352 176 352 224 1 2.1024259 1.0 0.0 0.0
162 384 224 384 176 1 2.1024259 1.0 0.0 0.0
w 352 176 336 176 0
w 384 176 368 176 0
w 352 224 336 224 0
w 384 224 352 224 0
w 368 176 352 176 0
L 224 272 176 272 0 1 false 5.0 0.0
w 384 272 352 272 0
162 416 176 416 272 1 2.1024259 1.0 0.0 0.0
w 416 272 448 272 0
w 416 176 448 176 0
162 448 272 448 176 1 2.1024259 1.0 0.0 0.0
w 416 176 384 176 0
w 352 272 336 272 0
162 384 272 384 224 1 2.1024259 1.0 0.0 0.0
s 272 176 336 176 0 0 false
s 272 224 336 224 0 0 false
s 272 272 336 272 0 0 false
w 384 272 416 272 0
162 352 224 352 272 1 2.1024259 1.0 0.0 0.0
r 272 176 224 176 0 100.0
r 272 224 224 224 0 100.0
r 272 272 224 272 0 100.0


-- 
~Mike

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