If I have understood everything correctly, I see a conflict when handling a large number of LEDs:
Parallel LEDs is dodgy, becouse if one fails, then all are bound to fail relativly soon.
LEDs in series requires fairly high voltages. Assuming one LED needs 1.4 Volts, I can power maximum 3 LEDs with 5 Volts.
Ok, I would like to power 30 LEDs which require 1.4 Volts at 20 mA. I would like to power them with 5V.
My reasoning is that even if I where to use 12 volts, I would end up using parallel circuits for this. So I thought I might want to combine a parallel & series set up:
I have 10 parallel circuits which each have 3 LEDs in series. The LEDs in series each have a 47 Ohm resister. I am limiting the whole system with a 1.5 Ohm resistor, but I am not sure if I really need that one. (I got lazy and didnt want to make the drawing any uglyer by adding arrows over all the LEDs. They are all LEDs. No regular diodes involved)
This seems terribly complicated… Any comments on how I am going about it?
Another problem I have: I was initially planning on powering this with the arduino. However If I am right I will be pulling 600mA which is way to much, correct? Even if I used an external powersource instead of USB power, I still could not get the amount of amps out of a digital pin. What about the 5V out pin? Can that Pin handle 600mA? Is there any simple way of powering this circuit, except for using an external powersupply and transistors for turning it on and off?
Ok, thats it for now. I feel like I am confusing myself. If anyone can take a look at this and give me some advice it would really be apreceated.