i'm decorating a 40' table with little dioramas that get lit up by randomly pulsing LEDs. I just bought a bunch of these but in different colors:https://www.sparkfun.com/products/8860
forward voltage around 3.3 for most or 2.2 for red and yellow. 80mA is forward current.
i used this http://led.linear1.org/led.wiz
webpage to calculate resistor size if i put them in series of 2 or 3 at a time. the resistors are mostly 1/2W or 1W. usually when i use them with these LEDs they run hot which is a little disconcerting.
i want to put around 6 leds (two or three series of them) into one tip120 which, going through a 1k resistor, goes into a PWM pin in arduino. There will be 24 leds in all and 4 tip120s.
then also i will use a second arduino to pulse 8 lights (4 series) going through 1 tip120, through 1k resistor, to an arduino pin.
can you put so many LEDs on one tip120? would a mosfet be better? will it be okay to do PWM using a transistor? do you think i need a heat sink for the transistor? any idea why the resistors become hot to the touch?
I want to power everything with a 12v, 5amp wall wort. here's a rough idea of what i mean (without actually having the craziness of 32 leds):