Sine Wave Generator
A simple sine wave generator based on a Wien bridge configuration of resistors and capacitors. Both voltage and frequency are variable.
What is L1, you ask? Why, it is a simple flashlight lamp.
Why doesn't it light up, you ask? Why, because it is used as a continuously-variable resistor. It serves as the feedback control component by changing the current it passes as the circuit tries to drive the frequency away from the setting you've selected.