Troubleshooting advice for basic transistor + pro mini setup

wvmarle:
Only if you stay within the limits of the transistor itself (current and power dissipation - for the pn2222a that's 600 mA and 625 mW respectively). With increasing voltage drop over the transistor the heat goes up accordingly! That's why you want to stay in saturation: the least voltage drop over the transistor, so the lowest power dissipation.

Makes sense... thanks a lot for the guidance!

Franck