So I'm trying to make an alarm clock that has a light that fades in before the alarm buzzer (faux sunrise, obviously less bright, to make waking up easier). So I'll need a high power LED (either one or two 3W, currently thinking one will do the job). I'm struggling with how I want to control the power and what to use to supply it.
CONTROL I know led's have limited dimming capabilities but trying to use what is there. I originally thought transistor but from what I know they are like a switch and I wont be able to get a fade action. But I saw this video (http://thecustomgeek.com/2011/08/01/controlling-high-power-or-high-number-of-leds-with-an-arduino/) and he has the LED fade and now I'm confused because everything I've researched says they are like a switch. Mine will only be a warm white not RBG if that influences anything. Second thought was using a variable resistor but I don't have any experience with them (nor with transistors but they seem more simple). Thinking about possible power usage it would need to be a 1-5W rated resistor depending on the power supply.
Both would be activated by the arduino. Also a product recommendation would be helpful or at least what to look for in a product specs and what not.
SUPPLY So I originally thought I would use the arduino wall adapter and splice in a set of wires for the LED so they would run in parallel. Thinking about this more I don't think its a great idea as the adapter is meant to just power the arduino. But I would like to avoid having two wall outlets occupied for the one device. So now I'm thinking have the ardunio power adapter and a second adapter inside of the clock casing. Both adapters would be in parallel from an extension cord from the wall.
The LEDs I bought are warm light 3W 3.6-3.8V 700mA according to the product details.
If my idea is right about the two adapters a 5V 0.7A would be a good choice right? (found an old phone adapter in my dad's bin of out-of-date electronics). I'd need a 2Ω 1W rated resistor correct? R=V/I=(5V-3.6V)/0.7A=2Ω and P=IV=(5V-3.6V)*0.7A=0.98W. Or at the low end I think 2.5V should activate the LED 4Ω 2W
THANK YOU!!! I really appreciate the help.