First, here's a good article on several methods to control a 2 pin
bicolor LED from one microcontroller port:
http://www.edn.com/index.asp?layout=3Darticle&articleid=3DCA6262537


Alternately:

Use a 4 terminal LED (such as a surface mount unit) where the red and
green are not internally connected (or use two seperate LEDs, and
explain to the boss that color blind people can't tell if it's red or
green, so two LEDs is more accessible).

Tie the Red anode to VCC through an appropriate current limiting resistor
Tie the Red cathode to the green anode and to the PIC pin
Tie the Green cathode to ground through an appropriate current
limiting resistor.

When high, the green lights, when low, the red lights.

When input, they might both glow if the combined forward voltage drop
is lower than your power supply, but they'll be going through two
voltage drops and two resistors, so they'll both be very dim.

If that's a problem, then add a 3.3v regulator just to power the LEDs.
 Then the voltage drop will be too much and they'll be off completely
when the pin is floating.  The PIC output at 5V won't hurt anything,
but make sure the Green resistor is sized for 5V, and the Red resistor
sized for 3.3V.

-Adam

On 6/19/08, Tom=E1s =D3 h=C9ilidhe <toe@lavabit.com> wrote:
>
>
> Olin Lathrop wrote:
> > This can be done, but will require some external hardware.
> >
> > Unless this is something you specifically want to do just to learn, use=
 a
> > bigger PIC and be done with it.
> >
>
> I've already got a 40-pin chip and I'm out of pins. Please elaborate on
> "external hardware".
>
> --
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