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Hello there everyone,

My question is, if the Arduino uses 5 V from the USB port and it simultaneously powers different pins @ 5v each where do those additional volts come from? Maybe a very basic question but I don't necessarily understand it. I have four LEDs in various ports and they all have appropriate supply and they have their resistors and everything works perfectly. Someone maybe can shine some light on that?
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I don't think you connected the grounds, Dave.
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What do you mean by "additional volts"?
5V == 5V
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Everything on the board uses the same 5V source. Let's look at your house with (say) 240V lights, does the mains voltage jump to 480V when you switch on a second light? No, what does happen is that the current will double, but the voltage stays the same.

Same with an Arduino, the CPU, LEDs, and many other components all run off the same 5V, but the more LEDs (for example) you have the more current is drawn.

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For example, I currently have 5 LEDs connected. These are white and each require 3.3 volts and consume 25mA . So, from my understanding, they all together need 9.9V and draw 75 mA. Each of them is connected to a single pin each. If the board is running off 5v I know it's enough for one LED but I don't quite get how each port is being provided the same voltage if 3.3 volts is already being used  the first LED unless they're in parallel. I'm sorry for the probably easy question but I'm trying to figure out how it all works.
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I don't think you connected the grounds, Dave.
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For example, I currently have 5 LEDs connected. These are white and each require 3.3 volts and consume 25mA . So, from my understanding, they all together need 9.9V and draw 75 mA
Try as I can, I cannot get any system of arithmetic I understand to come to the same conclusion.
In series, you'd need 16.5 volts, but only 25mA.
In parallel, you'd need 3.3 V and 125mA.
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I don't think you've quite understood the difference between 'voltage' and 'current'. You should probably watch some youtube footage, there are plenty of movies explaining the difference.

If a led needs 3.3V and uses 25mA current, adding more leds together in parallel (so all cathodes together, and all anodes together, basically laying all leds next to each other and solder all 'sides A' and 'sides B' together), the voltage needed will not change. You will still need to supply 3.3V, not more. "3.3 x 3 = 9.9" doesn't make sense here.The only thing that will increase is the current. 3 leds will make 3x25mA = 75mA.

You always need to be careful not to draw to much current (mA) on one pin, I believe on Arduino it's maximum 40mA per pin, and not more than 150mA all together.
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Each of them is connected to a single pin each...unless they're in parallel
Got it in one, they ARE in parallel.

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For example, I currently have 5 LEDs connected. These are white and each require 3.3 volts and consume 25mA . So, from my understanding, they all together need 9.9V and draw 75 mA. Each of them is connected to a single pin each.

Well,   your understanding is rubbish,  right there.    They would only need 9.9V if you connected them in series and tried to drive them from a single pin.

You need to learn some kindergarten grade electrical theory before you can progress any further.
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Perhaps he has connected three in series,   and two in parallel.   That would explain the ridiculous arithmetic.  5 x 3.3 = 9.9  ??   Or perhaps not.
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Listen, michinyon, I don't know if you noticed but the whole idea of forums, particularly open source ones; is to help out others who are getting started. It is not meant for others who have perhaps studied electronics or know just a bit more to find easy questions and pound them as "rubbish understanding" or "ridiculous arithmetic".

Of course I don't know, this is why I'm asking, if you find questions too far below your qualifications you can either:

A) Not answer altogether.
B) Be nice, help out someone who is trying to learn from others and make it a pleasant experience. For everyone.

The reason I ask is to know how to properly provide enough for all components in the project without frying them or providing lower than required voltage.
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Also, my error, I meant 3 LEDs, not 5.

If I have in series I see 9.9 V and 25mA if they're in parallel 3.3 v and 75mA.
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So, did MY answer help you? :-)
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