There are lots of techniques for multiplexing pins to
get more than 1 LED per pin.  Numerous microchip app
and design notes on this topic.  Look at how 7 seg
displays are done to get an idea (you may not need
drive transistors).  There was also a microchip
newsletter (iirc) article from about a year ago that
got a goodly number of LEDs per pin by using output L,
H and high Z (input) plus a bit of mental gymnastics. 


My favorite answer is a 12F509 + 2 74HC595s (to drive
up to 16 LEDs) but I suspect thats not what is being
looked for.

Phil

--- "John J. McDonough" <mcd@is-sixsigma.com> wrote:
> ----- Original Message ----- 
> From: "Dave Turner" <dave.w.turner@gmail.com>
> Subject: Re: [PIC] Best Pic for the job
> 
> 
> > Well, for low power consuption, you might want to
> try some of the new
> > nanowatt PICs.  I think the 16F87 and the 18F1320
> both have this.
> 
> The 16LF87/88 will run down to 2 volts, so a 3 volt
> lithium cell could be
> comfortable.  They have an onboard oscillator
> freeing up two more pins as
> I/O, and the oscillator is programmable so you can
> manage the power
> consumption even further.
> 
> > I think nearly all of the PICs should cover all
> these requirements,
> > except the tiny 8 pin devices, and probably not
> the 18 pins (unless
> > you use strobing).
> 
> He is only talking 6-12 LEDs plus a button or two. 
> An 18 pin part with an
> onboard oscillator is going to have 15 or 16 pins
> available, depending on
> whether you reuse !MCLR.  If you want to do ICSP and
> have obnoxious
> circuitry on all pins you might get down to 13 I/O. 
> With two buttons,
> that's still 11 LEDs.  If you insist on a crystal
> you are down to 9 LEDs,
> and that's worst case, still in the 6-12 range.
> 
> --McD
> 
> -- 
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