Hi Wesley. So you have a led matrix of 22 x 10 leds.
You are controlling it with two or more ULN2003's,
basically darlington NPN transistors.

If you want to "dim" the entire display for car use
I think you are right to look at doing this in hardware.
Yes you can use PWM etc in software but I don't think
that is always the best way. Sometimes hardware is
king.:o)

As a 22 x 10 matrix you must be using the ULN2003 as
the low side driver, what are you using as the high
side driver? Maybe you can modify your high side driver
to give variable current and use that to dim the leds??
Are you using a bank of PNP transistors to drive the
high side??

Maybe if you post a circuit there will be a few people
here willing to offer suggestions on how to give a
"dimming" effect for your led display. :o)
-Roman



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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