We found this circuit in an American 1980s documentation. The circuit uses a piezoelectric transducer unusual in our day. The transistor is general purpose type.
This circuit uses a PNP transistor to modulate a low power infrared LED. Observe the polarity of...
The integrated circuit used in this configuration is uncommon today. The diodes are for general use...
Although the integrated used originally is uncommon today, more modern operating equivalents can...