Im not sure what ohm to use. Does anyone have the calculation for figuring this out? Google is failing me...

Im hooking up LED light indicators on some on my switches (fan, fuel, ex).



EDIT: Nevermind. Found my answer here http://www.theledlight.com/ledcircuits.html

LED calculator
http://metku.net/index.html?sect=vie...calc/index_eng

 

http://www.raltron.com/cust/tools/voltage_divider.asp

 

You'll need a resistor wired in series that is 5 times the equivalent resistance of the rest of the load essentially.

 

LEDs are current controlled devices, a series resistor is used to limit current, not voltage.

 

Crap, I had no idea about this. Makes sense. Thanks

 

You don't need, or want to use a voltage divider to power an LED. Again, LED's are current controlled devices. You limit the current to the LED through a series resistor.
Using ohms law you can calculate the resistance needed (i.e. 13v/25mA = 520ohms). Led's have a rated forward current you should shoot for.
Being semiconductors, LED's do not have a linear relationship of voltage to current as many other things do. A small overvoltage percentage could result in double the current flow or more, burning out the led.

 

The easiest thing to do is buy LEDs that are rated for 12v usage.

 

No LED has a rated forward voltage of anywhere near 12volts. They simply have the appropriate resistors (usually around 400-500ohms).

 

I'm pretty sure that's what Rob/Shoebox meant. Simpler is always better, when the detailed tech explanations don't seem to be getting through. KISS

http://www.radioshack.com/product/in...ductId=2062569