Let's go back on topic.
Apologies for still not entirely understanding electrical current, but i hav 2 questions about ground.
- If I can have a resistor on EITHER side of an LED, could i also tie all of their cathodes together, then resistor, then ground? I am guessing not, since otherwise there would not be much need for bussed resistor networks. But why/
Do not apologise for asking questions if you have something you do not understand.
This question is more complicated than you might think.
You are only addressing the cathodes, not what happens with the anodes.
If you share all cathodes and a resistor, you should also share the anode with the same signal.
The resistor's presence is meant to control the current through the LED (and the resistor, as they are in series).
So you should look up the current and the forward voltage for that LED, and then use the resistor to meet those specifications.
If you have components in parallel (instead of in series), the current will go up.
Two (almost) equal LEDs in parallel will result in a double current figure.
So that means you need to use a different resistor.
The complication here is this:
What if you have 5 equal LEDs, cathodes tied together, a single resistor to GND, and anodes controlled (whatever way) separately.
Now your resistor has to be changed whenever you change the combination of LEDs to be lit.
This also means, that if you are using some circuit that has all LEDs lit at the same time, if one ceases, the others will suffer and cease too soon after that.
So there's two good reasons to use separate resistors.
If you have to use multiple LEDs to be lit at the same time, look into putting them in series.
You need the number of LEDs times the forward voltage to supply the set, but only once the forward current.
If one LED ceases, the other ones will also no longer be lit, but they will not be destroyed.
I hope this answers your question.
If not feel free to ask again.