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 configuration uses the 4 gates of a 7401 integrated circuit. The capacitors determine the...
This is a precision half-wave rectifier, suggested by Texas Instruments. Diodes are commonly used,...
This circuit is suggested by National Semiconductor in its 1994 Linear Applications Handbook. The...