From: "Frank Bemelman"
Subject: Re: controlling led brightness with variable resistor
Date: Tue, 21 Jan 2003 21:15:16 +0100
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NNTP-Posting-Date: 21 Jan 2003 20:15:25 GMT
"jt" schreef in bericht
> 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
> will show up. I'm after variable brightness, but not JUST that - these
> 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)
> 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.
I would not use bicolour leds, but seperate red and green. You can drill
plenty holes in the edges, and single leds are cheaper and brighter.
You could also add blue leds, and spin through the entire color circle.
I would drive the leds from 5V, using mosfets. A simple switcher to
make 5V from the 12V (National LM2576). A small PIC to generate the
pwm for the 3 mosfets.
Sphero made a nice drawing, using a digital encoder for setting the
color. I think he has some software too ;)
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