Ooh!  Ooh!  Finally someone who could use one of my tricks...

I had a similar deal, wanted to be able to dim a whole bunch of LEDs in an
array driven by a PIC.  I used an ADC input (though you don't need this,
you could just have 2 or more levels of dimming) to determine a time
constant to leave the LEDs on.  Lower input voltage to the control pin,
shorter ON time, less brightness.  The LEDs are driven via row/column
transistors with no current limiting resistors (reduced parts count) and
just one cheap, low-power pot to control the brightness.  It's got low
parts count and very little code.  I've got the thing written up on my web
page, http://www.botkin.org/dale/.  Hope it helps.

Dale

On Sat, 23 Jun 2001, Wesley Moore wrote:

> I am only driving LED's. I have a 22 x 10 matric of 3mm LED's. The reason I
> want to vary the voltage is to provide display dimming in the dark since the
> unit is destined for my car.
>
> Wesley
>
> On Fri, Jun 22, 2001 at 10:53:02PM +1000, Roman Black wrote:
> > Hi Wesley, the ULN2803 does not make output voltages,
> > it is a bunch of darlington transistors in a chip
> > designed to be either on or off.
> >
> > If you explain more about how many devices you
> > are driving, and what they are, and why you need to
> > vary the output voltage then many people can offer
> > suggestions.:o)
> >
> > If you need the ULN2003 datasheet I can email it to
> > you.
> > -Roman
> >
> > --
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> >
>
> --
> Wesley Moore                      http://www.1moore.org/
> RMIT - BEng (Comp Sys Eng)/BApp.Sc. (Comp Sci)  3rd Year
>
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>

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