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Hi folks. I saw that all is talking about leds, strips, hard codings, shields, motors etc.. Thats not helping beginners. So i wanted to make a General About Arduino topic for beginners to ask simple "Starter Logic" questions before get more pro on arduino. As one of my friends said ;
"There are no stupid questions! We all had to start at some point!"
I m the first! Haha. Okay in my researches i see that we supply arduino via usb and dc jack and vcc pin and also 5v pin. Usb feeds a clear 5v to operate. Dc jack and vcc pin has 7v-12v need because they integrated via a voltage regulator which gives arduino a clear 5v also. But 5v pin which meant to give u an Output for ur devices can be also used as a voltage Input! Wow. Okay.. but its lil dangerous because 5v pin has no voltage regulator so u need to be sure u give a clean 5V to this pin to not to fry ur board. Here is the case; i see in some of projects people give 5v from 5V pin. But in an article its said they dont advice this. But only extetnal supply i cld find is 5v. And also this will feed my led strips too. so i feel i must feed arduino with this 5v pin. Do i need to afraid or what?
Hi Stan,
thank you for starting this topic! 
First off, under normal circumstance (not much connected to the Arduino) a simple 2A 5V USB power-supply, for example from your phone, or a cheap one from AliExpress, eBay of Amazon, would do the trick. The 5V feed from the USB port of a computer is is sufficient as well - as seen when programming the Arduino.
If however, you need to power something that is power hungry, for example a LED strip, then a stronger power-supply is recommended.
Here we would see two scenario's;
Thx for the explanation Hans. I ve seen that article and i definitely have decided to make figure 5 already because i will need 5A to 10A. Hehe. Well its a big project. Ok then now i m sure i will 5V pin to feed my mega. But i think i will have a resistor between my strip and data pin as its said that way to protect the first led on the strip from power sparks(whatever is this i dont know but it sounds logical haha)
Haha, well, just keep in mind that figure only applies when the Arduino is not connected to your PC.
So while you're developing, you'd probably use figure 4 until your code is ready and the Arduino will run independently ... 
Oh yes yes. No pc connection while its powered from the external!! Indeed i noted that!! Haha. It would be soo bad to see the smoke from the chip!
... and the smoke from your PC would be even worse 
Haha yea but if i cant arrange true calculations about amperage and the true cable type then that 10A supply can fire up my room also.. wow i m little afraid now. I need a professional for that haha
Haha, well, it's better to have a wire that is too thick, then too thin - but you'll feel the wire getting warm when it's too thin
Yea i made some researches about that and i ve found this which is very popular ;
https://www.amazon.com/gp/product/B008L3QJAS?psc=1&redirect=true&ref_=oh_aui_detailpage_o08_s00
But i dont know the Diameter of the cable and i dont know how much diameter i need! Because if diameter is much then natural resistance of cable itself will reduce 5V( high school science lesson hehe) and if diameter is too low then firing up is a matter of time..
There are several sources where you can find this info (I've attached a chart as well - source).
For example the American Wire Gauge Table - which has a calculator at the bottom as well.
I usually do not worry too much, just when Amps go beyond say 5A, then I observe the wire used in the Power Supply and match that. After a bit of use I feel first by hand if the wire gets warm, and if i can barely feel it with my hands, then I hold the wire against my lips to see if I can feel it to get warmer or not. Hands first though! 
Oh I forgot to add: to use this chart for 5V, multiply the amps with 2 (since it's calculated for a 12V system, so we roughly can have twice the load).
Hmm okay i have a problem.. why i double the amperage. I no get it.. i need divide! No? Why? Haha. I m confused. Ok.
V=I.R
For example
12=6.2 but i need 5v. Leta say 6v
6=6.1. I keep 6A becauae it is what it ll take.
So the resistance of cable goes divided. So i need divide the number in chart. Not double. I m stuck now!!
And also in the link below i gave wire link it is 22ga and its used for arduino. I find 16ga in same website and it says for bus, boats and vehicles use!! I dont get.. 22 ga is Down of 16 ga?
http://www.firemountaingems.com/resources/encyclobeadia/charts/6404
Okay as I Thought the ga measurement goes opposite hehe. So higher ga means thinner cable ..okay. but i still no get why i Multiply becauae i ise not 12 i use 5v so current is lower so i need thinner ga so why i Multiply with 2 . I need divide 2 !
Simply put, the cable thickness is rated by wattage (I'm sure someone will tell me this is not 100% correct, since not all the lingo is 100% correct and there are a few other aspects that matter, but it will give you the basic idea).
Say a cable is rated for 120 Watt and we use 12V.
Watt = Volt x Amps
so
120 W = 12 V x X A
so X = 10. Running 12V this cable could handle up to 10A.
However, when we use the same cable for only 6V:
120 W = 6 V x X A
This makes X = 20, and this cable can handle 20 A at 6 V (see: V divided by 2, then A multiply by 2).
So now you see why Voltage and Amps calculate opposite.
For you other question: 22ga might not be suitable when 12ga is recommended. Thicker is better when it comes to the amount of power pushing through.
