Newbie Needs Help!

Hi
I am new to this and need some help. I want to play around with some LED's and see what I can do. I have a 3.6 volt 20mA 1100mcd and want to play around with it.

If I used 2 AA cells and one LED would I have to use a resistor? if so what size?

What would be the best number of AA cells to use with this?

2 AA batteries will be fine to run that LED directally. It wont power it at the arted power, so it wont be as bright as it could be, but it will work. These is a resistor calculator around somewhere in cyberspace (someone else may have teh link). 3 AA batteries and a resistor would be able to run it at its rated power.
Jeff

i think that there is a whole thread on electonics basics.. including the most basic rule: ohm's law... look int 'batteries included' thread i think it's there..

You can calculate the resitance needed pretty easy with this equation:

Voltage=current x resistance.. you can solve for any of the three pretty easily.

if you have 4.5V and want to end up with 3.6V at 20mA.. this is how it works:

you need to 'drop' the difference (4.5-3.6=0.9V) on the resistor.. and you have one other value (current).. you are looking for resistance.. so solving that equation you divide the voltage by the current.. or .9V/0.020ohm.. = 45 ohm..

the other important equation... Power = current x voltage... so you can calculate 3.6v x 20ma = 72mW power on the LED and .9x20mA = 18mW.. efficiency is not great at 80%, but that's the life of resistor ckts.. you could over drive a bit by reducing the resistor and it'll be more efficient... a great starter project to learn how to use ohm's law though.

-awr