Wow! I appreciate you taking the time to explain all this!
I will have to read the explanation several times to try and grasp it all lol!
I think I understand that transistors work via current and mosfets with voltage. So when you are picking a transistor to use, you are trying to pick one that will draw as little current as possible from the source (wemos pin in my case) to “turn on”. But it has to be able to supply enough current and voltage for whatever it is switching (relay in my case). So, you determine the resistor size (that connects to the transistors base pin) to limit the current draw from the source.
If you can’t use a resistor to limit the current draw to an acceptable amount based on the source (wemos output) data sheet, then you have to choose another transistor or go a different route? Maybe I’m getting closer to understanding?
Now, I am being difficult, as I stated in a previous post, I used a tip120 with the 2.1k resistor. Is that going to be a problem?
Will I be better or worse with it compared to the 2n2222, or is it a null point?
Is this what is referred to as a fly back diode?
Thanks all!