# SparkFun Forums

### Basic circuit questions

For the discussion of Arduino related topics.

### Basic circuit questions#180245

By fstim82
#180245
(I'm attempting to follow Vilros Ultimate Starter Kit Guide, Circuit #1)

Maybe I'm missing something but the guide book doesn't really seem to be teaching me anything about what I just connected. I'm having some trouble finding the right info online as well. I'm sure these are super basic questions, but I really don't know why things work the way they are (and to stress, I DO have it working). I'll summarize what I've done in case people here aren't familiar with the guidebook:

After uploading a program to the Arduino Uno to flash pin 13, I've wired pin 13 to breadboard e2, inserted a light at c2, c3, then have a 330 ohm resistor at a3, negative column, then a wire from negative column to GND on the Arduino. In addition to this, I've a wire from the 5v pin on the Arduino to the positive column on the breadboard. This gives me a flashing light and the example is concluded.

What I want to know is:

1. My understanding is that electricity flows in a circuit (which is a loop) from the negative terminal (pin 13?) to the positive terminal (5v pin?). However, the 5v pin is only connected to the positive column on the breadboard, and that isn't connected to anything at all. In fact, I can remove the 5v to breadboard+ wire altogether and everything keeps working (which sort of makes sense since nothing was connected after that anyway). The guide's schematic doesn't even show a loop. It shows pin 13 -> LED -> Resistor -> GND. No loop, so something isn't making sense to me. Why don't I need a loop to make this work, and why did they have me put in a pointless (to me anyway) wire?

2. I don't think I fully understand the ground concept either. It's kind of just a big endpoint for electricity to travel to, but in the case of a flashlight, where power flows from battery -, to light, to battery +, is the battery it's own ground? Is the + terminal the same thing as ground? That can't be right because if I connect 5v to the negative column, things turn off. (I imagine bad things would be happening if I were messing with something of higher voltage lol)

3. Finally, the resistor. Do they slow the entire circuit down simply by being present at any point in the circuit, or is there an order of operations kind of thing? In my mind, The flow would have hit the LED first, then the resistor, at which point the flow would be lessened. But I guess the chokepoint it creates would have the whole thing slowed down behind it just like rush hour? Maybe I just answered my own question, but I still wonder why the resistor came AFTER the LED. The purpose was to keep the light from burning out from too much energy, but wouldn't you want to put the resistor before the LED, even if "traffic" were to buildup quickly after it hit the resistor later on? Maybe it's a negligible thing, but am I at least thinking along the right lines?

### Re: Basic circuit questions#180269

By Ross Robotics
#180269
1. Pin 13 is the positive side of the loop.
2.
is the battery it's own ground?
Simply, yes. "Ground" is a reference point.
3. A resistor limits current. Think of current as water. Water flows through a pipe (wires). Current is presented as water flowing through a pipe. The faster the water flow, the higher the current.. So it doesn't matter where you put a limiting factor in the pipe, it will slow the current down through out the length of the pipe.

There is not enough space on this forum's server to answer the question "What is the basics of electricity." Nor do we want to type out the basics as this has been done literally tens of thousands of times on the web. Use Google. Read everything! Buy some books. Arduino is a learning tool so you can see electricity working first hand.

### Re: Basic circuit questions#180272

By Mee_n_Mac
#180272
1. My understanding is that electricity flows in a circuit (which is a loop) from the negative terminal (pin 13?) to the positive terminal (5v pin?).
Just wanted to address this point, because of the way current flow is defined, it might be confusing to you to read more. The actual flow of electrons is as you state it. Alas back in Ben Franklin's day they didn't know this. So the convention was to think of current as flowing from the + to the - in the circuit. Most everyone talking about current flow will use this convention so it's best to think of current flow this way.