Re: ATM A little electronic help on my Foucault tester

[Steve JB Bouton <sjbbouton@juno.com>]

What you need to do is put a resistor in series with the LED to limit
current flow.  First, what is the voltage of the power supply (or
battery) that you are going to use?  Subtract the voltage drop of the LED
from that value.  Calculate the value of the resistor using Ohm's Law,
which is Voltage / Current = Resistance.

Example- Using your Super Bright White, and a 3 Volt battery, you get:

(3V - 1.82V) / .02A = 59 Ohms

The closest standard value is either 56 or 62 Ohms; either will work
fine.

Hope this helps.

BTW, mcd is millicandela.  Candela is intensity.  Lumen is intensity per
a given unit of area.



On Mon, 3 Dec 2001 17:01:41 -0600 "James Taylor" <u2pilot@satx.rr.com>
writes:
> 
> I'm about to build my tester.  I need some electronic help.
> 
> I'm planning to use one of the Radio Shack bright (and big) LEDs.  
> All I
> need to know is how do I wire it so that I don't burn it out.  I 
> want to run
> it off batteries and put a pot on it so I can dim it if needed.  I 
> took the
> Heathkit Home Electronic course waaaay too long ago to remember 
> anything
> useful out of it.
> 
> Which one I should use is another discussion.  Right now I'm looking 
> for
> some electronics advice.
> 
> Here are the LED specs off the back of the package(s).
> 
> The Orange one:  Normal ops is 2V and 40mA.  300mcd
> 
> Green: normal ops 2.2V, 40mA. 350mcd
> 
> Super Bright White: 1.82V +/- .03V and 20mA.  This baby puts out 
> 5000mcd at
> 660nm wavelength.
> 
> There were some peak voltages and amps associated with them, but I 
> thought
> the nominal values were probably enough for this question and I 
> didn't write
> them down.
> 
> Oh, last thing.....what is the mcd unit given on those packages?  I 
> was
> expecting to see Lumens or something similar.
> 
> James
> 
> 
> 

________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today!  For your FREE software, visit:
http://dl.www.juno.com/get/web/.