TouchTheFishy:
Assuming my device needs 200mA and using a 2n2222 transistor (beta=300), I found that R1 needs to be of 8.3k Ohm.
Now I am stuck for the value of R2.
Not that it matters for this, but R1 needs to be 220 ohms or so if using a transistor as a switch. beta is not
relevant.