Is there a way to power a bunch of leds from an external power supply (battery), but control on/off/pwm with an arduino i/o pin? I'm not trying to create individually addressable leds (I'm fine will all of them acting as a single led). Basically, I want to power 100 leds from an external power source, but control them with an arduino. I hope this question makes sense. Any help/guidance would be tremendously appreciated.
Yes. Use a relay or MOSFET transistor in the same way that you would use these to control a motor.
Google "Arduino motor control" for many tutorials.
Ahhh, thank you so much!!! This is exactly what I was looking for. I hadn't thought of this because I typically use motor shields, but as soon as you said MOSFET...it clicked :)
So basically, a transistor will allow me to control a higher current (from an external battery), with the much lower current that comes out of the i/o port.