How does a single Arduino control dozens of LEDs?

Hi all,

I've seen a bunch of projects involving dozens (or hundreds) of LEDs being controlled by an Arduino. How does this work?

I imagine it somehow needs an additional controller with more i/o pins... What sort of addon would I be looking for if I wanted to do this? Can everything still be controlled by the Arduino programming, or would I need to program individual circuit chips?

I'm pretty new to Arduino and electrical engineering in general, and haven't been able to wrap my head around this. I'd much appreciate it if someone can shed some light.

Thanks!

First of all use the forum search and again you will not find plug and play projects you'll need to tailor them to your needs Hint see : 100 led's arduino ( in forum search ) , shift register , multiplexing , led driver circuit etc.

Thanks for your help, I appreciate it! I never would’ve known what to search for.

For anyone who stumbles in here with the same question, I found some really helpful info here: http://www.arduino.cc/en/Tutorial/ShiftOut

Here I show how to simulate PWM control using inexpensive 595 shift registers. http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1278251011

I personally stopped doing that and went for the easy solution using LEDs similar to the ones found in this post: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1275457576

Have fun :)