Found in American documentation from the 1980s, this circuit can be designed with equivalent components. The microphone can be of the piezoelectric type.
This circuit was obtained in the 1977 RCA CMOS manual. The circuit has the frequencies determined by the...
We found this circuit in a 2004 documentation. The circuit consists of a standard lamp for testing...
Found in a Popular Electronics of the 90s this configuration can be seen elsewhere on our site....