Ashley Roll wrote:
>

> > Another thought I just had (beware - its 2:30AM here, so
> > sentience is not guaranteed) was to have the LED setup like:
> >
> >
> >                            ^ V+
> >                            |
> >                           === Cap
> >                 ,-|<-,     |
> >  PIC PIN >------+    +-----+
> >                 '->|-'     |
> >                           === Cap
> >                            |
> >                            V GND
> >
> >
> > Then you float the pin.. When you want to light one of the
> > LEDs you set the pins data register to either high or low and
> > rapidly switch the pin between input and output.
> >
> > I've no idea if this would work, but you should be able to
> > draw some power thought the caps and may get enough to light the LED.


I really don't think it can work. You can only
charge or discharge the caps through the leds,
meaning that you will only be able to get an
amber light when oscillating, never a red or
green.

My circuit below tries to circumvent this problem
but was a 2 minute throw together and probably
won't work in the configuration shown. BUT the idea
is valid, ie, PIC pin tied low is green led on,
then when oscillating;
* short burst of LO pulls a chunk of charge
from 0.1uF C1, via CX and the diode. With a larger
CX value (1uF??) it should enable a decent percentage
of charge pulled from C1 without lighting the
green led. Then when PIC pin goes HI, current will
flow through the red led (and some via R1 and CX).

The only requirement to light the red led with ac
is too make sure that we draw more charge from
C1 with each short LO pulse than the charge we put
back in with each HI pulse that lights the red led.
Or any way we can discharge C1 without lighting the
green led.
Any thoughts?

---------------------------------
circuit below
---------------------------------
I have a feeling something like this could be made
to work, with some fiddling, to drive a bi-colour
led from one PIC pin. I don't know if it has any
real merits compared to the usual solutions.
At least it uses zero power in the "off" state
if it could be made to work.
-Roman


       +5v  ------------------------------------*------
                                                |
                   ?          1N4148            |
-----,     ,-------CX--------*--|<----,         R1  470 ohm
     |     |                 |        |         |
 PIC |     |                 '---RX---*         |
     |     |                          |         |
     |     |     ,----|<---,          |         |
     |     |     |   Green |          |         |
     |-----*-----*         *----------*---------*
     |           |         |                    |
     |           '---->|---'                    |
     |                 Red                      |
     |           Bi-colour LED                  C1   0.1uF
     |                                          |
-----'                                          |
                                                |
       Gnd  ------------------------------------*-----

            ,--------,  ,--------,  ,--------,
 Red on =   |        |  |        |  |        |
           -'        '--'        '--'        '--

 Green on =                                       (low)
           -------------------------------------

 Both off = ....................................  (high imp)

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