Advice on signal inverting circuit

Projects General Guidance
1

Okay, I have a project for a switch in my car. The problem is the input to the microprocessor in the car has to be a ground signal(low). The switch I am using is normally grounded and opens when activated. So I designed part of this circuit to invert the signal using a transistor. I don't know one thing though. Will the normally grounded switch make the entire circuit grounded once the switch is shut, essentially making the circuit always grounded. I don't know the resistance of the processor's input, so I'm not really sure how to calculate the voltage drop across the resistor. Any help?

2

That circuit will have a "low" of the drop across the diode, and across the transistor, so ~1.5V. May not be low enough for the arduino (which I think needs <0.8 for a low)
When the switch is closed, it will go up to 5V.

Ditch the 2 diodes, the 2.2K resistor can be 10K also. Then your low will be 1 transistor drop only, which would be enough.

3

Why not connect the switch directly to the Arduino and invert it in software?

4

Transistor provides some isolation?

5

or use an optocoupler for total isolation and do the inversion in software

6

or use an optocoupler for total isolation

Yes but the OP said:-

the input to the microprocessor in the car has to be a ground signal(low).

So you have no power to power the LED in the opto.
And anyway the opto isolator does the inversion for you.