I am trying to make an 8x8 RGB LED matrix with an Arduino Mega and 5mm common anode RGB LEDs. RGB LEDs will be on 1/16 of the time (4 at a time) but each LED in the RGB LED needs up to 20ma so 20x3=60 so I will need up to 60ma per RGB LED and 60x4=240 so I might need up to 240ma at once, but the Arduino Mega can only provide 200ma through 5v pins. I will buy needed components, but I'd prefer to us 1/4-watt resistors which I have, if possible.
thanks for any help.
Kindly read the pinned post re 'How to get the most from the forum'
what shape is the matrik (I don't know matrickis
8 rows of 8 64 total RGB LEDs square shaped
To control one row of 8 common anode RGB LEDs, with each LED individually on or off requires an anode line and 24 cathode+resistor lines, so 25 lines total.
A web search using the phrase "8x8 RGB LED matrix schematic" will turn up lots of useful images.
The forum archives likely has multiple examples of an 8x8, and 8x8x8 as well.
Where do I connect 5v and ground to a higher amperage supply, because as I mentioned the Arduino can only supply 200ma. I also want to have only 1/16 of the RGB LEDs on at a time and this looks like 1/8, that part I can figure out on my own though.
common anode RGB LEDs rely on current sinking but is it possible to current sink from a 5v external power source through the RGB LEDs and into the Arduino
yes, if the power supply commons are connected. Time for you to do some research about how that all works.
I did research and planned it all out. 
I even learned ohms law... finally.
My brain hurts when I look at all that wiring.
Have you ruled out using a neopixel matrix, or even single neopixles on a daisy chain?
Way less fun of a certain kind. Way more time making the LEDs do whatever is your goal.
It can fell like cheating. S'Ok.
a7
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To the line labeled "+5V" on the schematic, which incidentally is for common cathode RGB LEDs.
You can find these on many sites.
If you want big pixels, there are WS2811 12mm RGB bulbs wired as tree lights. A 50 bulb string runs < $20 but you could get 2 strings and splice 14 from one onto the end of the 50 of the other or even go for 10x10.
I'm a big fan of WS28xx. You feed it VCC (mine are 5V), GND and 1 pin serial data to address as many bulbs as you have and can power. WS2811 12mm bulbs diffuse the light, the bulbs glow as opposed to cast light cones.
When I consider RGB leds + transistors + wire + what-is-my-time-worth, I think they are a bargain!
If you choose colors from a palette, your selections can all be matching brightness/amps where bright white is 60 mA and still have 1000's of colors to pick from.
The FastLed library uses an array of 3 bytes per bulb. With 64 bulbs you can have row x 8 + col pixel positioning.
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