Well this isnt arduino related but it will eventually be when I use the arduino for a timer. Any ways here's what I'm trying to do:
On instructables theres a guy who made a uv led light box with 168 leds off of 12v.
So I have some 120 ohm resistors that the supplier sent me with my leds. She said to hook up 3 leds with 1 resistor in series.
Each panel will have 84 leds.
My question is will this work?
Here's the schematic: http://www.instructables.com/id/SWO38NYFTO53XNF/
r1-r28 will be replaced with 120ohm resistors..
It won't just "work", it will work (no quotes) just fine. 120R is just right to drop ~2.5V at ~20mA which is about what will be left of the 12V supply with three LEDs in series.
but the led's in the instructable are rated for 3.4v 20-25 ma
running @ 25ma that puts the optimum resistance at 72 ohms, the original document called for 75 ohms
using 120 ohm resistance on each bank of 3 will make them dimmer, though I seriously doubt you would be able to tell that much of a difference once 168 of them are going
120R is just right to drop ~2.5V at ~20mA which is about what will be left of the 12V supply with three LEDs in series.