LED wiring

Hi! I am wiring together LEDs to connect with my Duemilanove Arduino.

I am going to be using 2.2V LEDs at 20 milliamp. My question is, because each digital pin operates at 5 volts, i should only wire 2 LED in series off of each pin, right? Also if i put 3 parallel as i just described, will i be okay? (All of this using a 30ohm resistor for each circuit.)

Thanks for your help.
Also, If you have another/better idea of how to do this let me know.

My question is, because each digital pin operates at 5 volts, i should only wire 2 LED in series off of each pin, right?

Correct. With this setup, you will also need some form of resistors. I’m calculating about 33 Ohms for a safe circuit (as in no destroyed LEDs).

Also if i put 3 parallel as i just described, will i be okay? (All of this using a 30ohm resistor for each circuit.)

Parallel LEDs are slightly more complicated, but I think you meant series. If you are referring to series, I think the LEDs just wouldn’t light. Probably no damage done.

Here’s a nice little calculator for these things:

http://led.linear1.org/led.wiz

In series, current is constants, whilst voltage is cumulative.
In parallel, current is cumulative whilst voltage is constant.

Read this for info: http://www.allaboutcircuits.com/vol_1/chpt_5/1.html
Light Emitting Diodes (LEDs)

Also, if you put 3 led’s in parallel each with 30ohm resistors you will destroy your LED’s.

You may connect 2 led’s in parallel each with 165ohm resistors.

You won’t find a 165 ohm resistor so, so pick a higher valued resistor instead.

Basically you should have a resistor value greater than about 75R for 5V and one LED. This not only protects the LED but more importantly protects the output pin of the arduino. These are much more susceptible to damage than the LED.

http://www.thebox.myzen.co.uk/Tutorial/LEDs.html