A Wien bridge oscillator is essentially an RC Band Pass Filter with a high Q factor at the resonant frequency, and generates a nice sine wave. I wanted a simple audio-frequency test signal generator, and a Wien Bridge turned out to be perfect for the job.

As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub.

A good old LM324 does triple duty in the circuit:

• a non-inverting amplifier with a gain of ~3 provides the feedback required to sustain the oscillator
• one unit buffers a half-supply voltage to provide a "virtual ground" for the non-inverting amplifier
• a third unit buffers the output signal to avoid load interference with the oscillator

The LM324 doesn't have great upper and lower limits, and clipping is severe in the basic circuit. This is solved with diode stabilisation.

The result is a pretty decent sine wave at ~1.574kHz, very close to the theoretical resonant frequency of 1.592kHz.