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 16:31:00 GMT
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Viewed:
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672 times
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Hi all,
I've seen a lot of answers regarding the calculations for the resistor
values in this thread. If you want to be completely accurate, you have to
include the correct voltage drop across the LED for calculating the right
resistor. For most LED types the voltage drop is somewhere between 2 and 3
volts.
However, nothing will go badly wrong if you ignore these small differences.
The simplest interpretation of Ohm's law I can think of is:
Resistor-value = 7 / current-rating
So, when you buy LEDs, ask the salesperson for the correct current rating.
Example: For a LED with a current rating of 20 mA, the correct resistor
would be: 7 / 0.020 = 350 Ohms. The nearest available value is 330 Ohms. Use
1/4 w type resistors. In some cases 1/8 W resistors may run hot.
Even better: Simply tell the salesperson you want to run the LEDs with a 9 v
power supply and need resistors for it. Let them do the calculating.
Actually, I wasn't hoping this would turn out to be a discussion of the
intricacies of Ohm's law, but a discussion about running homemade add-ons
for Mindstorms.
Anyway, have fun.
Arjen
David Johnston wrote in message ...
> > Connect the LED through an
> > appropriate resistor to a 2x4 electric plate and glue the electric plate • to
> > the bottom of the brick.
>
> not being an electronic engineer, what is "appropriate"?
>
> D.
>
>
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Message has 1 Reply:
 | | Re: Homemade LED Bricks
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| Arjen Gerstel <a.gerstel@inter.nl.net> wrote in message news:FL3F92.CrE@lugnet.com... (...) As you may already know, I keep a set of pages devoted to homemade sensors and alike for the RCX at (URL) . I've posted quite a few homebrew sensor projects (...) (25 years ago, 12-Nov-99, to lugnet.robotics)
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