This tutorial on Arrays wires the resistors after the LEDs and connects them directly to ground. The way I understand it that wouldn’t limit the current to the LEDs. Is this a mistake on the part of the guy who made the video, or is it like a pull down circuit (I barely understand those) and the current is going the other way or something? I’m pretty sure it’s not the second one...
He has them wired as D5 and R3 in the image below.
A HIGH on Arduino pin D7 makes the LED D5 turn ON.
Billyprps:
This tutorial on Arrays wires the resistors after the LEDs and connects them directly to ground. The way I understand it that wouldn’t limit the current to the LEDs.
Your understanding in not correct. The current is limited by all resistive components in series. The resistor can be connected "before" or "after" the LED. You could divide the resistor into two and place one in front and one after.
Billyprps:
Is this a mistake on the part of the guy who made the video, or is it like a pull down circuit (I barely understand those) and the current is going the other way or something?
Its not a mistake. Its not like a pull-down circuit, but both are basic voltage dividers.
If you want to learn more about this, I recommend you get yourself a couple of resistors, a battery and a multi-meter. Then connect two of them in series and measure the voltage across each resistor and compare. Then switch the resistors and repeat. Try different values. Look the voltage divider wiki page.
I explain it like this:
Supposing you get in your car to drive 200 miles, somewhere on your journey there is road works that add and hour's delay to your journey. It does not matter where the road works are, near the start, in the middle or the end, what matters is the 1 hour delay they add. Same with resistance, what matter is how much resistance (delay in your journey) not where in the line of components it is placed.
The basic point about a series circuit is that the current is the same everywhere in the circuit, there's no way
the current can avoid the effect of the resistor - unless you are talking about extremely fast pulses or very high frequencies, all the components in the series circuit are seen equally, there is no "before" and "after".
The water-flow analogy is pretty useful, not so sure about the car-journey analogy as traffic can bunch up (charges in a series circuit can't bunch up as the current is the same everywhere(*)). Water flow in rigid
pipes can't bunch up either.
(*) To a very good approximation, until very high frequencies - a notable exception being an RF antenna.
MarkT:
The water-flow analogy is pretty useful, not so sure about the car-journey analogy
No analogy is perfect, different analogies work for different people.
