Hi , My English is not good. I have a problem when I Connect serial 4 leds. Each leds is 2.2 - 3 V . I connected to analog sixth. And all is disable . Lucky, I am connected parallel 4 leds , it's worked. But this is problem. I want to connect more leds. Just with one or two analog. Because my arduino uno just have 3 GND. I can't use more analogs. How to connect more leds using connect serial and parallel with 3 GND ?
I hope you answer soon. Thanks you !
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You can use as many grounds as you like. Just because there are only 3 grounds on the headers of the Arduino board means nothing. Probably the easiest way is to use a breadboard and connect the ground rail to one of the ground headers on the Arduino, then you can connect all the grounds you like.
But as for connecting a bunch of LEDs directly to an Arduino pin, definitely follow spycatcher2k's advice. You might want to do some research on the maximum current rating of the Arduino pins.
I try but it's not worked. I bought some transistor c1815 gr331. I try connect them but everything is not worked 
. Lucky , it still work but very very weak. Can you try connect them for me ? Just example. I have 5 leds, 1 transistor c1815 gr331, arduino uno board.
I very happy if you can do it.