Found in an Electronics Now from the 90s, this circuit uses components that are still common. The LM3900 is a transconductance operational amplifier.
We found this circuit in an American 1980s documentation. The circuit uses a piezoelectric transducer...
We found this circuit in December 1986, Radio Electronics magazine. It uses 3 inverters and has...
This circuit is from 1997 Linear Technology Applications. The circuit uses common components at...