These circuits were found in Exar documentation from the 90s. The circuits use both a small speaker and a piezoelectric transducer. The integrated circuit is not common today.
This high-gain circuit was found in an American publication from the 1990s. The circuit can use...
This circuit automatically controls the degree of illumination. As the circuit is from 2001, it...
This circuit was found in a Radio Electronics from April 1990. The circuit has 5 equalization...