Powering large quantities of LEDs and shift register fun

Hi there. So I'm new to arduino and electronics in general (only been playing with them for about 3 weeks now, but I'd like to think I've learned a lot).

But so here today a little box came in with 10 74HC595's (5 for me, 5 for my friend miguel) Played around a little. Can make them drive some LEDs to light up in pretty little patterns. But so for overall knowledge so that down the road when I'm plotting an idea. Say instead of running 24 LEDs off of the 3 of them I have hooked up at. Say I wanted to run 80 or so LEDs, or even more, Yeah putting a little more resistance in each LED circuit will do a bit more to protect the uno and the shift registers from dealing with too much amperage. But down the road (witht he cheap ones I have) once you start getting into the 1kOhms in each line, the lights are below visible in daytime (I've got some others that you can still see fine even with that but those cost a little more).

So here is my dilemma, or maybe more my question. Say you had your arduino driving the thing with its 5V signals just like normal, nothing wrong with that (maybe a little delay though for writing to the registers). But instead of hooking the registers power and ground to the uno, I were to make a 5V power source (or more like 4.5, which is still within the 74HC595's operating range) out of 3 AA batteries in series, and hook the ground on the register to the - on the battery. Just wondering before I contemplate trying this. Am I going to be making the magic smoke this evening if I go and test this?

You can have multiple power supplies in your circuit, one to power the Arduino, and one to power the shifters and LEDs. The only catch is, you have to have a common ground, so connect the battery's ground with the Arduino's ground.

The only catch is, you have to have a common ground, so connect the battery's ground with the Arduino's ground.

So umm, thats kinda confusing to me (sry havent taken an electronics class... ever). Common ground then. So yeah all the grounds go to the gnd pin on the uno. Does that mean the - on the battery stack goes to gnd as well?

Are you using two separate power supplies, or just one (being the 3 batteries)? If you're using just one, split the VCC line (being the + wire) and ground (being the - wire), one pair going to the Arduino, the other pair powering the shifters and LEDs. From the Arduino, run signal lines to the shifters. Nothing else.

That setup allows the shifters and LEDs to draw power directly from the batteries, and not the Arduino. The Arduino only controls the signal then.

This is much easier if you post a schematic of what you're trying to do.

Not really tying to do anything just wondering. And for the regards to this question, the uno itself is being run off of one of those Li-Ion battery shields. Meanwhile the LEDs and registers run off of the AA batteries or whatever) ... some sad attempts at drawing later.

Uuh so I think thats how they're supposed to go, all the registers hooked into the positive and negative of the batteries, then a branch off of the negative side to the ground pin?

At first glance, yes that's exactly what you need to do. The battery's - end, or ground, needs to be connected to the Arguino's ground as well. You can keep the LiPo on the Arduino as long as it is ONLY powering the Arduino, meaning you don't have any VCC (+5V or +3.3V) wire going from it to the shifters or LEDs, only the signal lines. And the 3 batteries are connected to the shifters and LEDs.

common ground is exactly what it sounds like. While you can have +5 going to one thing, +3.3V going to another, 1.8, 24...etc, they all have to share the same ground.

And it wouldn't be a bad thing if say, when building stuff up, and you had a 15V running around, it also had a common ground with the arduino? Wont make magic smoke?

Common ground is exactly that, ground. It sinks whatever comes to it. As long as you have proper VCC lines in the proper parts, and you do NOT have VCC lines between the two parts of your circuit, you are fine. A negative line on the other hand is bad, but ground is just fine.

haha wait... i just realized that my bad ignore my prior post =)

When working with LED displays or installations, I often (if not always) power the controller separately from the rest of the installation which often has a much higher voltage. As long as you have common ground between the two circuits, you're fine.

Ok then, TY guys. (off to probably break stuff nonetheless)

Nikarus: Ok then, TY guys. (off to probably break stuff nonetheless)

That's the nature of experimenting. Though with that also comes the possibility of creating/seeing the magic blue smoke. I've only seen it once so far. :)