my recent reads..

Atomic Accidents: A History of Nuclear Meltdowns and Disasters; From the Ozark Mountains to Fukushima
Power Sources and Supplies: World Class Designs
Red Storm Rising
Locked On
Analog Circuits Cookbook
The Teeth Of The Tiger
Sharpe's Gold
Without Remorse
Practical Oscillator Handbook
Red Rabbit

Tuesday, March 22, 2016

LittleArduinoProjects#197 Wien Bridge Audio Tone Generator

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.

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