After starting to learn about parallel circuits I’m questioning my understanding of circuits in general. I attached an image of my basic circuit which from my understanding is parallel and works as I expect. However, it seems to me that if I wanted to add something additional into this circuit that involved a resistor it would add to the overall “total resistance” and wold lower the brightness of my LEDs. So I guess my confusion is in how you separate circuits so they don’t interact with each other if that makes sense.

For example if I use two separate pins on the Arduino to bring over 5v to two different bread boards I think I would be working with two isolated circuits with their own “total resistance”. How does this work? Is something like this possible in my circuit or would I need a separate power supply?

DeviantSpark:
After starting to learn about parallel circuits.

The main thing is.... for components (or circuits) having 2 terminals, then connecting a bunch of 2 terminal components in parallel just means connecting ONE end of all those components together. And then you connect the remaining (OTHER) ends of those components together.

So all those components connected in parallel will have the same voltage applied across them all. That's what happens when you wire up components in parallel. The voltages across the 'parallel' terminals are all the same.

If you only work with DC voltages, larger resistance of a component results in lower current through the component.

Adding a resistor to the + and - sides of the battery will not effect the leds unless the battery is run down or you draw huge amounts of current and kill the battery.
Think of the battery as a constant voltage as long as it remains charged.

Adding such a resistor increases the load on the battery (more current flows) i.e. the overall resistance the battery sees decreases.

Taking 5v and ground to two different breadboards does not isolate the circuits since the wires are still connected to each other.

.

DeviantSpark:
For example if I use two separate pins on the Arduino to bring over 5v to two different bread boards I think I would be working with two isolated circuits with their own "total resistance". How does this work? Is something like this possible in my circuit or would I need a separate power supply?

If a single 5 V power supply is being used for two bread-boards..... then that is ok, as long as you know that your particular 5 V power supply can adequately supply the required amount of power to all of your circuits (on the two bread-boards).

However, it seems to me that if I wanted to add something additional into this circuit that involved a resistor it would add to the overall "total resistance" and wold lower the brightness of my LEDs.

If you add "something additional" in parallel it won't affect your existing LEDs unless to draw enough current that the voltage drops.

Adding something in parallel lowers the total resistance. Resistance is resistance to current flow... If you add another parallel path for the current, more current flows and the total resistance must be less.

Series & parallel circuits can get a little complicated, and it's probably hard to understand without taking an electronics class or studying an electronics book. It's all related to [u]Kirchhoff's Laws[/u] and the concept of [u]superposition[/u].

In your circuit, each LED and series resistor is connected directly to the battery so adding another LED & resistor doesn't affect the existing ones.

That's exactly how lamps and appliances are connected in your home. If you plug-in a 2nd lamp, the 1st lamp doesn't dim because they are in parallel and each lamp has it's own connection to the house power. With two lamps turned-on, more current flows and the total resistance is less.

UnoWatt:
Have you looked at Kirchoff’s Laws? The Current Law KCL says there is no net current at a node, ie what goes in, comes out. The Voltage Law KVL says there’s no net voltage in a loop, ie all the sources of voltage are cancelled by the drops.

Not sure if that helps, but I must confess I don’t understand the question.

Thanks for the information everyone. I have been studying Kirchoff’s voltage law but was not aware of the current law. I suspect it will answer many of my questions. I will research this and may have additional questions…