transistors
I Googled a little bit about transistors and I figured out I have a general understanding problem. Can I simply connect the emitter of the transistor to the GND of my microcontroller that controls the transistor but also to the GND of the 12V I try to control with the transistor, to close both circuits?
Would the circuit shown below work?
simulate this circuit – Schematic created using CircuitLab
"Earth" or "ground" in this case just means the point in the circuit the designer decided to call "zero volts", and use as a reference when measuring voltages elsewhere in the circuit - it does not imply an actual connection to the earth. I'd prefer to call that point "circuit ground", or "common", rather than "earth".
The important thing to notice in a common emitter circuit is that the emitter is common to both the input and output sides of the circuit
Use an analogue switch like this: -
It uses a logic supply rail as low as 1.6 volts but can switch signals that may be connected to supplies that are -5.5V to +5.5V. On-resistance is less than 1 ohm too.
Best Answer
The circuit you show in your scheme will not work. Chances are that the transistor is damaged. For a transistor connected as a switch, it is normal to place the load in the collector circuit, as I show below
simulate this circuit – Schematic created using CircuitLab
This is the basic way to connect a NPN transistor in the output of a microcontroller to activate a load.
When the output pin is in high, the transistor will conduct, feeding the load, in this case an LED. The value of the base resistance depends on the supply voltage of the microcontroller and the maximum current that support. The value of the collector resistor depends on the source Vcc, and the load that would like to activate.
This way, you can share the GND connection between the microcontroller and the power supply to the load.