LED Resistor
Hi Simon,
Actually, it's rather easy! Personally, I don't worry about all the calculation involved in find'n the right resistor. I'll just put a pot of, say, 5K ohms in series with the LED and slowly decrese the resistance until the LED shows a comfortable brightness. Then I'll measure the resistance with an ohm meter and that's the value of resistor I use. Rather unortodoxed, but it achives the same results, really.
U should also keep in mind, that different LEDs have differing current requirements, along with different brightnesses. If U know how much current an LED needs for moderat operation, then it's just a matter of using ohm's law to figure out the resistor. Also, it doesn't matter what side the resistor is on of the LED. It can be on either side.
BTW, for an ordinary LED and a 12 volt supply, I've used about a 1K ohm resistor and this has always worked.
As was mentioned in, I think it was 1 of the other replies, if U get an LED with a built-in resistor, then don't worry about adding another one... just connect it straight to yer 12-volt supply, and that's it.
Hope this helps.
Cheerz!
Bob