Subject: Re: controlling led brightness with variable resistor
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Date: Tue, 21 Jan 2003 15:44:13 -0400
NNTP-Posting-Date: Tue, 21 Jan 2003 14:39:36 EST
Organization: WorldCom Canada Ltd. News Reader Service
"John Fields" wrote in message
> On Tue, 21 Jan 2003 14:02:22 -0400, "jt"
> >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.