Found in a 90s Popular Electronics, this circuit is based on a common CMOS component. The circuit triggers a buzzer by approaching objects from an antenna.
This circuit was found in a 1980s Intersil documentation. The integrated circuit used is not...
Although it is a common configuration today, these circuits were taken from an old publication. The...
This circuit, from an old publication, can also use modern transistors. Note that the unit is...