First of all I'm quit new to electrical engineering. I had it 3 years in class but I didn't do well.
So here is what I plan. I got some shift-registers (74HC595) Which I'll set with an arduino mega 2560. With this I'd like to light up an LED. First I thought I could do it without any other circuit by just adding the right resistor to the 5V lane of the register.
But I noticed that the register can handle up to 700mW so it wouldn't be possible and I think that the idea overall is bad. So I decided to add transistors to the circuit.(2N3904)
So my question is, if I need a resistor in front of the Base of the transistor? If so what value or let me know how to calculate it so I can answer it myself for the secont transistor. (see second question down here)
And I got one more question to it. I'd also like to disable LED's by disabling the mass with an transistor. Can I just do it as shown above?
(To mention this here. I'll use it to light up 75LEDs (25RGB) in 5 Layers. By disabling the mass of a layer I can set one layer of leds at once. This will be mulitplexed to handle each led)
Update: So in total it should be something like this to handle more then one LED:
Since i got kathod LEDs it should need to be like this:
Calculation should be simmelar right?