This isn't strictly a Raspberry Pi question as the project is now using an Arduino Nano but I'm programming it through the Pi so fair's fair.
I've currently got the board flashing and flickering several LED's (separate pins) and it's working as expected. Now I want it to do the same with strings of LED's (I'm sacrificing some battery powered ones, the cheap Christmas type) so I figure I'll need to use a transistor.
I know the Nano will supply 5V at a max of 40mA and the LED's work on 4.5V at, let's say, 200mA (not measured but it's a figure).
The LED's will have a separate supply and I know I need some resistor between the Nano and the transistor's base.
Given the information I have how do I work out what spec of transistor I need and what value resistor?
I've been Googling a while now and still stumped, even the online calculators I've found need more info that I have so not lazy, just confused.