50+ RGB LEDs Doing Same Thing

I have read this previous topic and found it incredibly useful:

http://arduino.cc/forum/index.php/topic,122631.0.html

I just have a few further questions if anyone could further answer them!

The current needed for his 10 RGB LED project only need 600mA, for 50+ RGB LEDs I would need 3A minimum. I can't find a power supply that is 7.5V and 3A. For more RGB LEDs will I need more voltage too?

Also, I believe that whatever power supply I do need, I plug directly into the Arduino then use the Vin pin to supply the LEDs. Is this correct? Are there dangers to doing this? Is there a better, safer option?

Basically is there anything I should know about expanding his project from 10 RGB LEDs to 50+ LEDs? If I expand this project from 50 to 100 LEDs, will I need to completely rewire and change the resistors and increase the voltage/current?

Thanks for anyone that is able to help! I'm quite new at this and I decided I want to attempt to build an LED strip from scratch in order to learn more about circuitry rather than just buying a pre-made strip.

It doesn't need to be 7.5V, as long as it can provide at least the minimum 3A that you need, the PSU itself can be 12V. Just regulate the voltage down to what you need it to be. I drive LEDs with 12V and 24V supplies all the time. Add the appropriate resistor for the voltage and current needed and you're good to go. Granted, this means you can't use a stock Arduino by simply plugging it in to the PSU. You 'll have to either build a separate circuit to regulator that voltage, or cook your own Arduino-clone. Neither are particularly hard to do.

Thanks for the reply! I have a few questions just to clarify!

Towards the end they suddenly mention an Atmega328. What is the point of this? I don't understand it, just seems to complicate the overall project.

Why can't I plug the 12V 3A PSU directly into the Arduino then run that power out the Vin plug? It says an Arduino Uno is capable of handling 12V with an absolute max of 20V.

Why are there resistors before each transistor and what value should they be? Do the transistors "know" the proper current to supply when activated or do I program that? I want to make sure I don't blow my lights out!! Also will I need transistors that can handle 3A each? Do those exist? I can't find any!

If I go with a 12V PSU, I calculate I will need the following resistors:

Red - 490 so 510 Blue - 430 so 470 Green - 435 so 470 Since those aren't standard resistances I would round to the second number because you always want to play it safe and go to the closest value above the calculation right?

And last, on the diagrams on that post I don't see how to wire the anodes for the LEDs. The color strips are accounted for but how would I connect them all to the power supply? Just hook them all right up in series or parallel with the Vin output??

The LEDs I'm using are:

http://www.noodlehed.com/ebay/datasheets/HH-1000CRGBW810.pdf

Why can't I plug the 12V 3A PSU directly into the Arduino then run that power out the Vin plug?

Because the diode between the power jack and Vin is only rated at 1A.

Why are there resistors before each transistor

They are not transistors they are FETs. They protect the arduino from too much current.

I would round to the second number because you always want to play it safe and go to the closest value above the calculation right?

Yes

I don't see how to wire the anodes for the LEDs.

To the +ve of the power supply.

Ok thanks for clarifying those questions! Last question...what gauge of wire should be sufficient for this project??

I would use stranded wire 7/34 should do. That is 7 strands of 34 AWG wire this is the same as 7/0.16 7 strands of 0.16mm diameter wire. Or thicker will not do ant harm.

Are your LEDs 4-terminal or 6-terminal? If they are 6-terminal (i.e. not common anode or common cathode), you can connect several in series. This lets you use a higher voltage, lower current supply, which makes the design easier.