Hello! I'm new to electronics, or more specifically, physical electronics. I'm a developer, but I'm not a technician. I recently received the Student Kit in order to begin my electronic adventure; thus far, I've grasped the most of what is mentioned in the courses, but I've run into two challenges.
I'm at the "TRAFFIC SIGNALS" class and I'm having problems understanding the circuit:
1 - The resistors are here to supply enough energy to the LEDs to turn on but not too much that they burn out, so why are they behind the LEDs?
2 - In addition, the pull-down resistors article, which describes the method of pull-down resistors, shows that the current flow is from GND to digital pin 2, isn't it meant to be the other way around?
3 - Another thing about that circuit is that the lesson states that the top-pins for the button ALWAYS communicate EVEN IF THE BUTTON IS NOT PRESSED, so why isn't the current flowing through them when the button is not pressed when the current appears to be going directly to GND to Pin 2 without passing through the top-pins of the button?
Last issue or question should I say is why do we measure everything in volts? The lessons always asks me to measure the voltage between two points, shouldn't we be measuring the current instead?
I'd be grateful if someone could answer those questions and explain how the circuit works; I realize it's a lot, but I still don't get it after reading, analyzing, and verifying everything on my own.
P.S. I can supply links to other schematics, but I'm only allowed to provide two because I'm a new user.