Hello there. I have a RGB LED strip (not of those that you can control each LED individually), but I need your suggestions and advices in these issues:
- I'm gonna use an Arduino Nano for my project.
- The strip uses 12 volts, so can I use that voltage to power up my Nano board?
- I want to fade in and out the LEDs, so I need to know which pins give me a PWM output (and what number they have in the IDE).
- Which would be the best MOSFET transistor for my kind of LED strip?
- I'm not quite sure, but what if my LED strip has common cathode?
- Does the MOSFET's gate need a pull-off resistor?
I hope you understood my questions and I will appreciate your attention.
And by the way, the RGB LED strip that I was talking about from the beginning, is one of those that the four pins are: Red, Green, Blue, V in or Ground.
Yes you can power the both with the same supply.
Those strips are not common cathod, you ground the R G or B lines to make it light.
PWM pins have a ~ next to them in the board. What pins these are depend on the board you have.
Get a logic level FET.
A FET does not need a pull down resistor but it is a good idea.
There are lots of examples on the net for this sort of circuit. Google is your friend.
AOI514 from digikey.com works well.
I have 32 on this board to drive LED strips with 74H595 to drive the gates, pulldown resistor to hold the gate low should the 595 outputs be disabled.
Lucario448:
I'm gonna use an Arduino Nano for my project.
Okay, fine 
Lucario448:
The strip uses 12 volts, so can I use that voltage to power up my Nano board?
Yep, just connect it to Vin
Lucario448:
I want to fade in and out the LEDs, so I need to know which pins give me a PWM output (and what number they have in the IDE).
Google is you friend 
Lucario448:
Which would be the best MOSFET transistor for my kind of LED strip?[
The first logic level N-channel MOSFET you can find. Like IRLML2502, IRF7313 or IRL3705
Lucario448:
I'm not quite sure, but what if my LED strip has common cathode?
No, common anode, way easier to drive 
Lucario448:
Does the MOSFET's gate need a pull-off resistor?
Like said before, you don't need it per se but a pull down connected to the gate will keep the LED's off when the Arduino is in reset/starting. So it's a good idea 
OK thank you guys. Now I realized that I missed to ask you something: what value does the "pull-down" resistor must have in my case?
Thanks again 