Could someone please explain to me on how to use a resistor?

littlemal · Post by **littlemal** » Thu Mar 09, 2006 10:17 am

Thanks everyone!!! I think i'm getting it now!!

(A.J. Franzman The led have, is off of a cd player that I hacked into)[/quote]

A.J. Franzman · Post by **A.J. Franzman** » Thu Mar 09, 2006 6:09 pm

littlemal wrote:The led have, is off of a cd player that I hacked into

In that case, the typical current is probably 20 mA. There are a few LEDs that handle more, and a very few older "high efficiency" types that can't take that much, but 20 mA is a good value to use for 99.99% of "unknown" LEDs.

Regarding the voltage, if you tell us what color it lights we can make a fairly good ballpark guess. Blue and white are typically in the 3.2 to 3.6 volt range (3.5 being fairly common); red, orange and yellow are typically 1.8 to 2.2 volts (usually 2.2); and green typically 2.2 to 2.6 volts.

littlemal · Post by **littlemal** » Thu Mar 09, 2006 8:48 pm

It lights red..

A.J. Franzman · Post by **A.J. Franzman** » Thu Mar 09, 2006 11:21 pm

9.0 V - 2.2 V = 6.8 V
R = 6.8 V / 0.02 A
R = 340 Ω

The next higher standard values are 360 Ω and 390 Ω. You probably won't find either of those at Radio Shack, though. If you still have the CD player that the LED came from, you might find a resistor in it of the right value, though it will probably be surface-mount. I have lots of old junked electronics that I scavenge parts from and I can usually find a resistor of almost any needed value in 1/4 watt through-hole style.