Arduino as a potentiometer.

Hello i have this circuit that i would like to have some automation on. How make arduino power the circuit about 9 volts. And i would likke to change the voltage output. How can i do this.

You can use a DAC (Digital to Analog Converter) Ic. You send it a number and it puts out a voltage. You can get them in many different versions with different voltage handeling capabilities and different precision.

You can also get digital potentiometers that can be controlled by a signal from the Arduino. Perhaps you could give us some more details about what you're trying to do? Remember that the Arduino will need to be connected to the same Ground as the circuit you're trying to control, i.e. there won't be any electrical isolation.