Funny.... I have posted this circuit many months ago. Suddenly it is listed as private. That's why I post it again.
Push the switch to start the circuit.
Use the Poti on the left to regulate the output of the MOSFET between 0% (off) and 100%(on) using PWM.
***UPDATE***Middle Poti changes offset and the right one the frequency (~430Hz - 3kHz).
I have build this circuit on a breadboard. I had to adjust the window resistors on both sides of the Potentiometer (the 33k resistors) to make it work correctly. Also the oscillating frequency is different, but that doesn't matter. The circuit works fine in real.
