I'm a newbie with the electronics stuff here and want to do the RGB Led projects with Atmega88, but i have problems how to choose the right resistors for my projects. I will use 4 RGB leds which has the common cathode and connect it with the PNP transistors. The datasheet from the LED shows:
2 x Blue - 4.5V
1 x Red - 2.5V
1 x Green - 2.5V
Current - 20mA
NPN transistor- BC639?
PNP transistor-which one?
So the total current (Ic) that flows will be 80mA for red and green and 160mA for blue right?
Pls guide me to build this project.