Is possible to drive several 3V 30mA LEDs directly via Analog output pins so I can dim them? How much output power can Arduino give?
I would measure what is the analog output value which gives 3V and slide from 0 to that value? Will it work? Do I need external power or can I use USB power?
Thanks
The ATmega168 datasheet says it can support up to 40ma per pin with at most 200ma across all pins. So you should be able to drive up to 6 leds with 30ma at the same time on the 6 analog output pins.
USB power should be sufficient.
As you probably know, you need dropping resistors between the pins and the leds to limit the current. For 3v leds, 68 ohms gives around 30ma
Do I need 68 Ohm resistors even if I use only 0-128 as analog output?
yes
LED + resistor = ALWAYS -> to save the life of the LED and the I/O port since the LED resistor is about CURRENT not VOLTAGE.
But then do I need to use 0-128 as analog output or full range?
I can not find that small resistor, what happens if I take 5K one?
what happens if I take 5K one
Then you will get so little current through the LED that it will be too dim to see.