Here is a part of my schematic.
K pin from LCD is connected to NPN transistor. A pin is connected to Vcc, 5V.
Base is connected to uController. It is Atmega16. 5V supply.
I am using BC547 transistor as it is showed at the picture.
Electrical Characteristics form datasheet:
So the question is how can i calculate resistance of Rb?
I found some calculators online and there's always Vi, explained as the input switching voltage or the input trigger voltage. I am not sure what it refers to.
Also do i need resisor on collector too?