I need some help and/or resources for understanding basic circuits. I am a smart enough guy, but for some reason, I just can't "get" a few things about circuits. I have read several introductory books including Brindley's Starting Electronics, Mims's Getting Started in Electronics, and Massimo's book. I even have Horowitz & Hill on my shelf. The programming is not an issue at all; it's just the topology of the circuits that puzzles me.
Here is where I get stuck. Maybe someone here can give me an explanation or refer me to a reference that I need to fill the gap in my knowledge. I get circuits per se, e.g., where I see a loop as in Figure 4-4 in Massimo and I get the concepts of series, parallel, Ohm's law, how to calculate resistance for resistors in series, parallel, etc. Let me say that I know obtaining this basic knowledge and theory kind of goes against the "Arduino way" of skipping the basics, but I feel that my design of circuits needs to have a basic understanding of how things work.
Where I get stuck is when texts move from a circuit such as in Figure 4-4 or Figure 5-4 in Massimo (i.e., where I see a loop) to a topology like in Massimo Figure 4-6.
Once I figured out that a voltage source and ground mark the "ends" of the circuit in my mind (similar to the + and – terminals of a battery in a DC circuit), I see that there is a circuit in Figure 4-6 from the 5V source to one push button terminal, out the other push button terminal, through the resistor, and to ground. At first, I didn't understand how the wire going to pin 7 was involved in a circuit. It just seemed to dead end.
After seeing the corresponding schematic in Appendix D, I see that pin 7 is at ground, so that there is a second parallel circuit from the 5V source to one push button terminal, out the other push button terminal, then to pin 7 on the board.
Now, my question becomes: why do we need both of these circuits in parallel? Why do we need the circuit that goes through the push button and resistor to connect the 5V source to ground? Why can't we just have one circuit that goes from 5V source, through the push button, through a resistor, then to pin 7 to apply a voltage to pin 7 when the button is closed? I anticipate that one answer will be to figure this out by building my proposed circuit and seeing what happens (the Arduino way). I don't have a board yet though.
In a similar way, Figure 5-6 and Figure 5-7 confuse me.
Am I thinking about circuits wrong? Is there a better model or scheme for understanding what is going on?