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From: firstname.lastname@example.org (Paul Mathews)
Subject: Re: controlling led brightness with variable resistor
Date: 21 Jan 2003 16:27:37 -0800
NNTP-Posting-Date: 22 Jan 2003 00:27:37 GMT
"jt" wrote in message news:...
> "John Fields" wrote in message
> > On Tue, 21 Jan 2003 14:02:22 -0400, "jt"
> > wrote:
> > >I want to controll the brightness of a bunch (maybe 30 or more) of led's
> > >with a knob. So far I think that what I'll need is some sort of analog
> > >chip driving a power transistor. Suggestions on part numbers or
> > >(better)methods are welcome.
> > ---
> > Not knowing what kinds of LED's you have in mind or what kind of
> > power source you have available, I'd be tempted to put them all in
> > series and drive them with a variable constant current source.
> > How about a little more data as to the LED characteristics and what
> > you want to do about the power supply?
> Well, it is a bit more complicated.
> What I'm after is a 12V dash panel with a bunch of LED's edge-lighting it.
> This'll have some engraving through a surface painted black, so the legends
> will show up. I'm after variable brightness, but not JUST that - these are
> red/grenn bicolour LED's, so I want to drive the red and green portion in
> variable complementary amounts, as well as having an over-all brightness
> control. Brightness and hue, in essence.
> I was guessing about 1 amp for about 30 LED's at reasonable (max) currents;
> hoping for something simple, cheap, and robust. Series makes me think of
> christmas tree lights - don't want them all going out it one goes bad.
You can't beat the microcontroller approach for cost and efficiency.
However, if you're not in a position to do the programming, consider
the LED driving chips available from Toshiba and others. They come in
many flavors. In N America, Toshiba is available through Marktech
see the LED FAQ at http://www.pioneernet.net/optoeng/LED_FAQ.html
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