Transistor and its behavior

Other Hardware General Electronics
1

Hi, i have a problem with my circuit, it works, but i don't know why.
I want to power an LED strip using arduino, tip122 transistor, 1k ohm resistor and 12 volts from 8 AA batteries.

Problem is that when i connect arduino ground to the ground on breadboard (to "-" side of batteries), Led strip does get a little bit brighter, when P2 is HIGH, but never turns off, only gets dimmer a bit, when p2 is LOW
when i connect arduino ground to the drain/emitter of the tip122 it works (turns off completely, when p2 is LOW), but i don't know why, and i think that this isn't the way it should work.

I have attached two fabulous fritzing drawings, hope it will help you help me. :slight_smile:

And sorry if im being stupid, i am new to the arduino and don't know the flamability of this comunity.
(please, don't be like xda or stackoverflow people, please :smiley: )
And another apologies for any english mistakes i've made.

arduino ground confusion.png
arduino ground confusion.png2514×1278 308 KB

arduino ground confusion2.png
arduino ground confusion2.png2514×1278 309 KB

2

Arduino Ground must be connected to battery -.

Pinout of TIP-122 is Base, Collector, Emitter, in that order.

You've got the collector and emitter switched - you want the negative side of the load going to the collector, and the emitter connected to ground.

3

123 BCE

Why do you have the collector connected to the negative terminal of the battery? It isn't acting as a transistor, that is why it isn't responding the way it should.

Please consider learning to draw schematics, they are much clearer. And you'll often catch errors.

4

Thank you, i accidentally made my batterypack reverse so the red wire is "-" fuck, at least i know why it was doing all those funky things. Thank you for your kindness. I tried to draw schematics too, but i was like, what if i messed up with breadboard or something :slight_smile: sorry again.