Re: LED question for electronics wizards

Robert Reynolds wrote:
Chuck wrote:
I would connect one of the LEDs in series with the 500 ohm resistor to your
proposed power source, and see if the results are what you need.
Then, I might try two 500 ohm resistors in series, and if really brave two
resistors in parallel. (This may or may not cause the LED to fail.)
LEDs have a brightness range and a current range. The idea is to have them
as bright as you need but no brighter.
Conventional LEDs normally need between 20-30 milliamps of current to work
properly.

These are rated at 3 to 3.8 volts and 25 mA. I appreciate Ray's advice about using a larger source that's limited by resistors, for greater endurance. That makes sense. I'll do the math and see what the optimum voltage source is for 25 mA and 500 ohms.

You don't _have_ to use 500 ohms -- you just need to limit the current appropriately. 500 ohms may waste a lot of voltage, which would make your batteries necessarily heavy.

The idea with an LED is that you need to give it the right _current_ (hang the voltage), and when you do that it'll impede that current with _some_ voltage in it's range. Just what that voltage will be depends on the LED and the temperature. So you calculate the right resistance for your voltage source over it's range, and the LED's over theirs.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
.

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