Controlling a large number of LEDs

I've been playing around with the Arduino board and have gotten it to control a LED based on a series of inputs quite well. I now want to get that signal (it's an RGB signal controlling an RGB LED) to drive several hundred LEDs. They don't need to be controlled individually - all the LEDs will do the same thing at the same time, but obviously the board cannot drive that many LEDs. I have a separate power pack that should be able to have the right current, but I don't know how to connect the LEDs to the signal to the power source in a way that makes sense... Any ideas from folks with more analog electronics experience than I?

well its not really analog, you will be still digitally manipulating the leds, your eye / brain is the component smoothing that out to analog interpretation

(yea ok you could but ...)

what you need to do is have something that can take a weak current and modulate a larger current, this is a generic text book description of a transistor, course your typical transistor will only hold a handful of ma at best

so depending on how much current your calculations show is what kind of parts we can suggest (mosfet ssr etc)

least your not trying to control hundreds of rgb leds (so led count * 3) individually, that would GREATLY increase complexity

I have a separate power pack that should be able to have the right current

Hundreds of RGB LEDs are going to draw a lot (make that A LOT) of current. Not only will the power supply need to handle providing that much current, but so will the wires connecting the LEDs and resistors. Have you actually determined how many LEDs there will be, what the current requirements are for each one, and what the total current requirement will be?

Can your power supply actually deliver that much?

it’s an RGB signal

Really? What’s an RGB signal?

Re: the current / power source, I was thinking of using a number of lithium 9 V batteries. Each battery should be able to power 40 LEDs for an hour or so (1,200mAh), which is enough for my needs. So 10 batteries should be able to power 400 LEDs. I don't need common wiring for all the LEDs (I could use more batteries, for example), except that they have to share the signal...

And by RGB signal I simply meant taking the 4 pins that drive my lone, single RGB LED right now.

Or am I thinking about this the wrong way?

Since your LEDs probably have a voltage in the range of 3V or so, you might find it advantageous to improve the power supply efficiency with a switching regulator. A google search for "switching regulator 7805 replacement" turns up several candidates. This one has been mentioned here in the past. Favorably, iirc.

It's kinda spendy, but might be worthwhile to get extra runtime and reduced heat.

Thanks, Ran. I don't know much about switching regulators. From what I read online after your reply, it's basically a more efficient way to deliver a fixed voltage. I couldn't find many example circuits, though - how would I use them to drive my LED array?

The over-simplified explanation is that a switching regulator works kinda like the PWM you're using to drive the LEDs: instead of turning the extra input voltage into heat, it turns it off and on very fast so the average output is the voltage you want.

The three key things you need to know are that they're more efficient, more expensive, and that some of them don't work correctly unless you have a minimum load. E.g., a 5V 5A power supply might not give you a clean 5V if your system only draws 100mA. Since your LEDs will probably have some "all off" time, you need to check the specs on any regulator you're considering to make sure it doesn't require a minimum load.