Subject:
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Re: Homemade LED Bricks
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 12 Nov 1999 13:49:02 GMT
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Viewed:
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1047 times
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Russell Nelson <lego-robotics@crynwr.com> wrote in message
news:14380.1027.389073.809639@desk.crynwr.com...
> Yeah, but it's not 9 volts. It's 9 volts minus the .7 volt drop
> across the LED. Plus some of the new eyeburner LEDs take as much as
> 40ma, so you have to know how much current the LED takes. Give it too
> much and you greatly shorted its life.
Its not .7 volts for an LED its more like 1.8volts and its takes 20ma if you
want for full brightness for a typical display LED. (or more for a
eyeburner like Russells) Also, I see more like 8.5volts out of the RCX not
9.
So (8.5-1.8)/330 = 20ma. Now things get worse with blue LEDs they have
something like a 3volt drop. The bottom line is: If you use a series
resistor that is larger than 330 nothing will go wrong. The LED just won't
be quite as bright and what is the fun in that?
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Message has 1 Reply:
 | | Re: Homemade LED Bricks
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| (...) The forward voltage of the LED does depend on the colour. In an electronics catalogue, the following values are listed, but do vary for specific devices. Red typically 2v Yellow 2.1v Green 2.2v Blue 3.3v White 3.6v ///// < .. > > - (...) (25 years ago, 12-Nov-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: Homemade LED Bricks
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| Keith Miller writes: > basicly.. it's i*r=v where i = current in amps and r = resistance in ohms > and v = voltage in volts.. > so.. > If we want to find out the resistor's value.. we re arrange it like so.. > r = v/i > so 10 millamps (typical led (...) (25 years ago, 12-Nov-99, to lugnet.robotics)
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