Whoop! I fried my first LED the other night....

[solderman]

I had nearly the exact same thing happen to me too, 2 weeks ago! I couldn't figure out why that happened, then I checked my resistors - I was using 2.2 OHM resistors, not 2.2k resistors. I nearly burned out a 2nd green LED before I figured it out too.

I usually use 2.2k or 4.7k resistors, no matter what size or colour of LED - is that bad? Is there an easy chart to tell you what size R to use?

Jacob

Calculate the resistor that limits the current floating through a LED like this.
As Always, Ohms law applies

Lv/La=Lr

Where:
Lv= is the sum of the circuit voltage minus the forward voltage for the LED, normally (normally 1,6V for a red, 2.2v for yellow and green, 3,6 for white and blue but check the LED data sheet)
La= is the nominal current for the LED, 20mA for a red LED but check data sheet.
Lr= is the resistor to use.

In a 9 volt circuit with a normal red LED this is (9-1,6)/0,02=370. 390 is the closest standard resistor. However I always use min 680 not to risk the LED or 1k if I am to use the circuit with 9-18V for better headroom if it's an OD etc.

So, No you are not wrong to use 2.2 or 4.7 it will only affect the brightness of the LED but protect it good.