> On Mon, 15 Sep 1997, Shane Nelson wrote:
>
> > Hi guys,
> >
> > I'm in need of some advice regarding multiplexing seven seg
> > displays. I have 4 displays on 12 i/o pins, and have two
> > concerns:
> >
> > 1) Visibility.
> >         What is the optimum "on time" vs "off time" for best
> > visibility, while at the same time having enough remaning cpu
> > time to be able to handle various other tasks?
> >
> > 2) Current consumption.
> >         How do I determine how much current the leds are going to
> > need, and how can I keep these values w/in the current specs of
> > the pic?  All the microchip literature seems to suggest that you
> > can drive leds directly. I've been doing it that way but have a
> > feeling I've been exceeding current specs on the i/o ports.
> >
> >
> > Thanks for any help! :)
> >
> > -Shane.

If you use an emittor follower on the PIC pin (that drive the LEDS), you
can charge a cap through a diode. The LED draws its current from the cap
via a current limiting resistor. This will introduce some latency, but
your
LED's will be switched on 100% and won't POP if your program freezes.

I don't particularly feel like ASCII art, but if you want me to, I will
attempt to draw it...

--
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za
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